From a2a46f629446af0935e8ebbbd7cdb55e395f79f3 Mon Sep 17 00:00:00 2001 From: Joe Malin Date: Mon, 14 Nov 2011 10:51:16 -0800 Subject: DOC CHANGE: New Content Provider topics Change-Id: Ib5507f4c9ecce3aea51cd39310e3f4990c9b3070 --- docs/html/guide/guide_toc.cs | 22 +- .../topics/providers/content-provider-basics.jd | 1215 ++++++++++++++++++++ .../topics/providers/content-provider-creating.jd | 1215 ++++++++++++++++++++ .../guide/topics/providers/content-providers.jd | 994 ++-------------- 4 files changed, 2532 insertions(+), 914 deletions(-) create mode 100644 docs/html/guide/topics/providers/content-provider-basics.jd create mode 100644 docs/html/guide/topics/providers/content-provider-creating.jd diff --git a/docs/html/guide/guide_toc.cs b/docs/html/guide/guide_toc.cs index e239bb1dadf9..dbb6ad32a27a 100644 --- a/docs/html/guide/guide_toc.cs +++ b/docs/html/guide/guide_toc.cs @@ -87,10 +87,24 @@ Content Providers
  • diff --git a/docs/html/guide/topics/providers/content-provider-basics.jd b/docs/html/guide/topics/providers/content-provider-basics.jd new file mode 100644 index 000000000000..40b5c3fd4c7b --- /dev/null +++ b/docs/html/guide/topics/providers/content-provider-basics.jd @@ -0,0 +1,1215 @@ +page.title=Content Provider Basics +@jd:body +
    +
    + + + +

    In this document

    +
      +
    1. + Overview +
        +
      1. + Accessing a provider +
        2. +
      2. + Content URIs +
        3. +
      +
      2. +
    2. + Retrieving Data from the Provider +
        +
      1. + Requesting read access permission +
        2. +
      2. + Constructing the query +
        3. +
      3. + Displaying query results +
        4. +
      4. + Getting data from query results +
        5. +
      +
      3. +
    3. + Content Provider Permissions +
      4. +
    4. + Inserting, Updating, and Deleting Data +
        +
      1. + Inserting data +
        2. +
      2. + Updating data +
        3. +
      3. + Deleting data +
        4. +
      +
      5. +
    5. + Provider Data Types +
      6. +
    6. + Alternative Forms of Provider Access +
        +
      1. + Batch access +
        2. +
      2. + Data access via intents +
        3. +
      +
      7. +
    7. + Contract Classes +
      8. +
    8. + MIME Type Reference +
      9. +
    + + +

    Key classes

    +
      +
    1. + {@link android.content.ContentProvider} +
      2. +
    2. + {@link android.content.ContentResolver} +
      3. +
    3. + {@link android.database.Cursor} +
      4. +
    4. + {@link android.net.Uri} +
      5. +
    + + +

    Related Samples

    +
      +
    1. + + Cursor (People) +
      2. +
    2. + + Cursor (Phones) +
      3. +
    + + +

    See also

    +
      +
    1. + + Creating a Content Provider +
      2. +
    2. + + Calendar Provider +
      3. +
    +
    +
    + + +

    + A content provider manages access to a central repository of data. The provider and + is part of an Android application, which often provides its own UI for working with + the data. However, content providers are primarily intended to be used by other + applications, which access the provider using a provider client object. Together, providers + and provider clients offer a consistent, standard interface to data that also handles + inter-process communication and secure data access. +

    +

    + This topic describes the basics of the following: +

    + + + +

    Overview

    +

    + A content provider presents data to external applications as one or more tables that are + similar to the tables found in a relational database. A row represents an instance of some type + of data the provider collects, and each row in the column represents an individual piece of + data collected for an instance. +

    +

    + For example, one of the built-in providers in the Android platform is the user dictionary, which + stores the spellings of non-standard words that the user wants to keep. Table 1 illustrates what + the data might look like in this provider's table: +

    +

    + Table 1: Sample user dictionary table. +

    + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
    wordapp idfrequencylocale_ID
    mapreduceuser1100en_US1
    precompileruser14200fr_FR2
    appletuser2225fr_CA3
    constuser1255pt_BR4
    intuser5100en_UK5
    +

    + In table 1, each row represents an instance of a word that might not be + found in a standard dictionary. Each column represents some data for that word, such as the + locale in which it was first encountered. The column headers are column names that are stored in + the provider. To refer to a row's locale, you refer to its locale column. For + this provider, the _ID column serves as a "primary key" column that + the provider automatically maintains. +

    +

    + Note: A provider isn't required to have a primary key, and it isn't required + to use _ID as the column name of a primary key if one is present. However, + if you want to bind data from a provider to a {@link android.widget.ListView}, one of the + column names has to be _ID. This requirement is explained in more detail in the + section Displaying query results. +

    +

    Accessing a provider

    +

    + An application accesses the data from a content provider with + a {@link android.content.ContentResolver} client object. This object has methods that call + identically-named methods in the provider object, an instance of one of the concrete + subclasses of {@link android.content.ContentProvider}. The + {@link android.content.ContentResolver} methods provide the basic + "CRUD" (create, retrieve, update, and delete) functions of persistent storage. +

    +

    + The {@link android.content.ContentResolver} object in the client application's + process and the {@link android.content.ContentProvider} object in the application that owns + the provider automatically handle inter-process communication. + {@link android.content.ContentProvider} also acts as an abstraction layer between its + repository of data and the external appearance of data as tables. +

    +

    + Note: To access a provider, your application usually has to request specific + permissions in its manifest file. This is described in more detail in the section + Content Provider Permissions +

    +

    + For example, to get a list of the words and their locales from the User Dictionary Provider, + you call {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + ContentResolver.query()}. + The {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + query()} method calls the + {@link android.content.ContentProvider#query(Uri, String[], String, String[], String) + ContentProvider.query()} method defined by the User Dictionary Provider. The following lines + of code show a + {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + ContentResolver.query()} call: +

    +

    +// Queries the user dictionary and returns results
+mCursor = getContentResolver().query(
+    UserDictionary.Words.CONTENT_URI,   // The content URI of the words table
+    mProjection,                        // The columns to return for each row
+    mSelectionClause                    // Selection criteria
+    mSelectionArgs,                     // Selection criteria
+    mSortOrder);                        // The sort order for the returned rows
+
    +

    + Table 2 shows how the arguments to + {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + query(Uri,projection,selection,selectionArgs,sortOrder)} match an SQL SELECT statement: +

    +

    + Table 2: Query() compared to SQL query. +

    + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
    query() argumentSELECT keyword/parameterNotes
    UriFROM table_nameUri maps to the table in the provider named table_name.
    projectioncol,col,col,... + projection is an array of columns that should be included for each row + retrieved. +
    selectionWHERE col = valueselection specifies the criteria for selecting rows.
    selectionArgs + (No exact equivalent. Selection arguments replace ? placeholders in the + selection clause.) +
    sortOrderORDER BY col,col,... + sortOrder specifies the order in which rows appear in the returned + {@link android.database.Cursor}. +
    +

    Content URIs

    +

    + A content URI is a URI that identifies data in a provider. Content URIs + include the symbolic name of the entire provider (its authority) and a + name that points to a table (a path). When you call + a client method to access a table in a provider, the content URI for the table is one of + the arguments. +

    +

    + In the preceding lines of code, the constant + {@link android.provider.UserDictionary.Words#CONTENT_URI} contains the content URI of + the user dictionary's "words" table. The {@link android.content.ContentResolver} + object parses out the URI's authority, and uses it to "resolve" the provider by + comparing the authority to a system table of known providers. The + {@link android.content.ContentResolver} can then dispatch the query arguments to the correct + provider. +

    +

    + The {@link android.content.ContentProvider} uses the path part of the content URI to choose the + table to access. A provider usually has a path for each table it exposes. +

    +

    + In the previous lines of code, the full URI for the "words" table is: +

    +
    +content://user_dictionary/words
+
    +

    + where the user_dictionary string is the provider's authority, and + words string is the table's path. The string + content:// (the scheme) is always present, + and identifies this as a content URI. +

    +

    + Many providers allow you to access a single row in a table by appending an ID value + to the end of the URI. For example, to retrieve a row whose _ID is + 4 from user dictionary, you can use this content URI: +

    +
    +Uri singleUri = ContentUri.withAppendedId(UserDictionary.Words.CONTENT_URI,4);
+
    +

    + You often use id values when you've retrieved a set of rows and then want to update or delete + one of them. +

    +

    + Note: The {@link android.net.Uri} and {@link android.net.Uri.Builder} classes + contain convenience methods for constructing well-formed Uri objects from strings. The + {@link android.content.ContentUris} contains convenience methods for appending id values to + a URI. The previous snippet uses {@link android.content.ContentUris#withAppendedId(Uri, long) + withAppendedId()} to append an id to the UserDictionary content URI. +

    + + + +

    Retrieving Data from the Provider

    +

    + This section describes how to retrieve data from a provider, using the User Dictionary Provider + as an example. +

    +

    + For the sake of clarity, the code snippets in this section call + {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + ContentResolver.query()} on the "UI thread"". In actual code, however, you should + do queries asynchronously on a separate thread. One way to do this is to use the + {@link android.content.CursorLoader} class, which is described + in more detail in the + Loaders guide. Also, the lines of code are snippets only; they don't show a complete + application. +

    +

    + To retrieve data from a provider, follow these basic steps: +

    +
      +
    1. + Request the read access permission for the provider. +
      2. +
    2. + Define the code that sends a query to the provider. +
      3. +
    +

    Requesting read access permission

    +

    + To retrieve data from a provider, your application needs "read access permission" for the + provider. You can't request this permission at run-time; instead, you have to specify that + you need this permission in your manifest, using the + + <uses-permission> element and the exact permission name defined by the + provider. When you specify this element in your manifest, you are in effect "requesting" this + permission for your application. When users install your application, they implicitly grant + this request. +

    +

    + To find the exact name of the read access permission for the provider you're using, as well + as the names for other access permissions used by the provider, look in the provider's + documentation. +

    +

    + The role of permissions in accessing providers is described in more detail in the section + Content Provider Permissions. +

    +

    + The User Dictionary Provider defines the permission + android.permission.READ_USER_DICTIONARY in its manifest file, so an + application that wants to read from the provider must request this permission. +

    + +

    Constructing the query

    +

    + The next step in retrieving data a provider is to construct a query. This first snippet + defines some variables for accessing the User Dictionary Provider: +

    +
    +
+// A "projection" defines the columns that will be returned for each row
+String[] mProjection =
+{
+    UserDictionary.Words._ID,    // Contract class constant for the _ID column name
+    UserDictionary.Words.WORD,   // Contract class constant for the word column name
+    UserDictionary.Words.LOCALE  // Contract class constant for the locale column name
+};
+
+// Defines a string to contain the selection clause
+String mSelectionClause = null;
+
+// Initializes an array to contain selection arguments
+String[] mSelectionArgs = {""};
+
+
    +

    + The next snippet shows how to use + {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + ContentResolver.query()}, using the User Dictionary Provider as an example. + A provider client query is similar to an SQL query, and it contains a set of columns to return, + a set of selection criteria, and a sort order. +

    +

    + The set of columns that the query should return is called a projection + (the variable mProjection). +

    +

    + The expression that specifies the rows to retrieve is split into a selection clause and + selection arguments. The selection clause is a combination of logical and Boolean expressions, + column names, and values (the variable mSelection). If you specify the replaceable + parameter ? instead of a value, the query method retrieves the value from the + selection arguments array (the variable mSelectionArgs). +

    +

    + In the next snippet, if the user doesn't enter a word, the selection clause is set to + null, and the query returns all the words in the provider. If the user enters + a word, the selection clause is set to UserDictionary.Words.Word + " = ?" and + the first element of selection arguments array is set to the word the user enters. +

    +
    +/*
+ * This defines a one-element String array to contain the selection argument.
+ */
+String[] mSelectionArgs = {""};
+
+// Gets a word from the UI
+mSearchString = mSearchWord.getText().toString();
+
+// Remember to insert code here to check for invalid or malicious input.
+
+// If the word is the empty string, gets everything
+if (TextUtils.isEmpty(mSearchString)) {
+    // Setting the selection clause to null will return all words
+    mSelectionClause = null;
+    mSelectionArgs[0] = "";
+
+} else {
+    // Constructs a selection clause that matches the word that the user entered.
+    mSelectionClause = " = ?";
+
+    // Moves the user's input string to the selection arguments.
+    mSelectionArgs[0] = mSearchString;
+
+}
+
+// Does a query against the table and returns a Cursor object
+mCursor = getContentResolver().query(
+    UserDictionary.Words.CONTENT_URI,  // The content URI of the words table
+    mProjection,                       // The columns to return for each row
+    mSelectionClause                   // Either null, or the word the user entered
+    mSelectionArgs,                    // Either empty, or the string the user entered
+    mSortOrder);                       // The sort order for the returned rows
+
+// Some providers return null if an error occurs, others throw an exception
+if (null == mCursor) {
+    /*
+     * Insert code here to handle the error. Be sure not to use the cursor! You may want to
+     * call android.util.Log.e() to log this error.
+     *
+     */
+// If the Cursor is empty, the provider found no matches
+} else if (mCursor.getCount() < 1) {
+
+    /*
+     * Insert code here to notify the user that the search was unsuccessful. This isn't necessarily
+     * an error. You may want to offer the user the option to insert a new row, or re-type the
+     * search term.
+     */
+
+} else {
+    // Insert code here to do something with the results
+
+}
+
    +

    + This query is analogous to the SQL statement: +

    +
    +SELECT _ID, word, frequency, locale FROM words WHERE word = <userinput> ORDER BY word ASC;
+
    +

    + In this SQL statement, the actual column names are used instead of contract class constants. +

    +

    Protecting against malicious input

    +

    + If the data managed by the content provider is in an SQL database, including external untrusted + data into raw SQL statements can lead to SQL injection. +

    +

    + Consider this selection clause: +

    +
    +// Constructs a selection clause by concatenating the user's input to the column name
+String mSelectionClause =  "var = " + mUserInput;
+
    +

    + If you do this, you're allowing the user to concatenate malicious SQL onto your SQL statement. + For example, the user could enter "nothing; DROP TABLE *;" for mUserInput, which + would result in the selection clause var = nothing; DROP TABLE *;. Since the + selection clause is treated as an SQL statement, this might cause the provider to erase all of + the tables in the underlying SQLite database (unless the provider is set up to catch + SQL injection attempts). +

    +

    + To avoid this problem, use a selection clause that uses ? as a replaceable + parameter and a separate array of selection arguments. When you do this, the user input + is bound directly to the query rather than being interpreted as part of an SQL statement. + Because it's not treated as SQL, the user input can't inject malicious SQL. Instead of using + concatenation to include the user input, use this selection clause: +

    +
    +// Constructs a selection clause with a replaceable parameter
+String mSelectionClause =  "var = ?";
+
    +

    + Set up the array of selection arguments like this: +

    +
    +// Defines an array to contain the selection arguments
+String[] selectionArgs = {""};
+
    +

    + Put a value in the selection arguments array like this: +

    +
    +// Sets the selection argument to the user's input
+selectionArgs[0] = mUserInput;
+
    +

    + A selection clause that uses ? as a replaceable parameter and an array of + selection arguments array are preferred way to specify a selection, even the provider isn't + based on an SQL database. +

    + +

    Displaying query results

    +

    + The {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + ContentResolver.query()} client method always returns a {@link android.database.Cursor} + containing the columns specified by the query's projection for the rows that match the query's + selection criteria. A {@link android.database.Cursor} object provides random read access to the + rows and columns it contains. Using {@link android.database.Cursor} methods, + you can iterate over the rows in the results, determine the data type of each column, get the + data out of a column, and examine other properties of the results. Some + {@link android.database.Cursor} implementations automatically update the object when the + provider's data changes, or trigger methods in an observer object when the + {@link android.database.Cursor} changes, or both. +

    +

    + Note: A provider may restrict access to columns based on the nature of the + object making the query. For example, the Contacts Provider restricts access for some columns to + sync adapters, so it won't return them to an activity or service. +

    +

    + If no rows match the selection criteria, the provider + returns a {@link android.database.Cursor} object for which + {@link android.database.Cursor#getCount() Cursor.getCount()} is 0 (an empty cursor). +

    +

    + If an internal error occurs, the results of the query depend on the particular provider. It may + choose to return null, or it may throw an {@link java.lang.Exception}. +

    +

    + Since a {@link android.database.Cursor} is a "list" of rows, a good way to display the + contents of a {@link android.database.Cursor} is to link it to a {@link android.widget.ListView} + via a {@link android.widget.SimpleCursorAdapter}. +

    +

    + The following snippet continues the code from the previous snippet. It creates a + {@link android.widget.SimpleCursorAdapter} object containing the {@link android.database.Cursor} + retrieved by the query, and sets this object to be the adapter for a + {@link android.widget.ListView}: +

    +
    +// Defines a list of columns to retrieve from the Cursor and load into an output row
+String[] mWordListColumns =
+{
+    UserDictionary.Words.WORD,   // Contract class constant containing the word column name
+    UserDictionary.Words.LOCALE  // Contract class constant containing the locale column name
+};
+
+// Defines a list of View IDs that will receive the Cursor columns for each row
+int[] mWordListItems = { R.id.dictWord, R.id.locale};
+
+// Creates a new SimpleCursorAdapter
+mCursorAdapter = new SimpleCursorAdapter(
+    getApplicationContext(),               // The application's Context object
+    R.layout.wordlistrow,                  // A layout in XML for one row in the ListView
+    mCursor,                               // The result from the query
+    mWordListColumns,                      // A string array of column names in the cursor
+    mWordListItems,                        // An integer array of view IDs in the row layout
+    0);                                    // Flags (usually none are needed)
+
+// Sets the adapter for the ListView
+mWordList.setAdapter(mCursorAdapter);
+
    +

    + Note: To back a {@link android.widget.ListView} with a + {@link android.database.Cursor}, the cursor must contain a column named _ID. + Because of this, the query shown previously retrieves the _ID column for the + "words" table, even though the {@link android.widget.ListView} doesn't display it. + This restriction also explains why most providers have a _ID column for each of + their tables. +

    + + +

    Getting data from query results

    +

    + Rather than simply displaying query results, you can use them for other tasks. For + example, you can retrieve spellings from the user dictionary and then look them up in + other providers. To do this, you iterate over the rows in the {@link android.database.Cursor}: +

    +
    +
+// Determine the column index of the column named "word"
+int index = mCursor.getColumnIndex(UserDictionary.Words.WORD);
+
+/*
+ * Only executes if the cursor is valid. The User Dictionary Provider returns null if
+ * an internal error occurs. Other providers may throw an Exception instead of returning null.
+ */
+
+if (mCursor != null) {
+    /*
+     * Moves to the next row in the cursor. Before the first movement in the cursor, the
+     * "row pointer" is -1, and if you try to retrieve data at that position you will get an
+     * exception.
+     */
+    while (mCursor.moveToNext()) {
+
+        // Gets the value from the column.
+        newWord = mCursor.getString(index);
+
+        // Insert code here to process the retrieved word.
+
+        ...
+
+        // end of while loop
+    }
+} else {
+
+    // Insert code here to report an error if the cursor is null or the provider threw an exception.
+}
+
    +

    + {@link android.database.Cursor} implementations contain several "get" methods for + retrieving different types of data from the object. For example, the previous snippet + uses {@link android.database.Cursor#getString(int) getString()}. They also have a + {@link android.database.Cursor#getType(int) getType()} method that returns a value indicating + the data type of the column. +

    + + + +

    Content Provider Permissions

    +

    + A provider's application can specify permissions that other applications must have in order to + access the provider's data. These permissions ensure that the user knows what data + an application will try to access. Based on the provider's requirements, other applications + request the permissions they need in order to access the provider. End users see the requested + permissions when they install the application. +

    +

    + If a provider's application doesn't specify any permissions, then other applications have no + access to the provider's data. However, components in the provider's application always have + full read and write access, regardless of the specified permissions. +

    +

    + As noted previously, the User Dictionary Provider requires the + android.permission.READ_USER_DICTIONARY permission to retrieve data from it. + The provider has the separate android.permission.WRITE_USER_DICTIONARY + permission for inserting, updating, or deleting data. +

    +

    + To get the permissions needed to access a provider, an application requests them with a + + <uses-permission> element in its manifest file. + When the Android Package Manager installs the application, a user must approve all of the + permissions the application requests. If the user approves all of them, Package Manager + continues the installation; if the user doesn't approve them, Package Manager + aborts the installation. +

    +

    + The following + + <uses-permission> element requests read access to the User Dictionary Provider: +

    +
    +    <uses-permission android:name="android.permission.READ_USER_DICTIONARY">
+
    +

    + The impact of permissions on provider access is explained in more detail in the + Security and Permissions guide. +

    + + + +

    Inserting, Updating, and Deleting Data

    +

    + In the same way that you retrieve data from a provider, you also use the interaction between + a provider client and the provider's {@link android.content.ContentProvider} to modify data. + You call a method of {@link android.content.ContentResolver} with arguments that are passed to + the corresponding method of {@link android.content.ContentProvider}. The provider and provider + client automatically handle security and inter-process communication. +

    +

    Inserting data

    +

    + To insert data into a provider, you call the + {@link android.content.ContentResolver#insert(Uri,ContentValues) ContentResolver.insert()} + method. This method inserts a new row into the provider and returns a content URI for that row. + This snippet shows how to insert a new word into the User Dictionary Provider: +

    +
    +// Defines a new Uri object that receives the result of the insertion
+Uri mNewUri;
+
+...
+
+// Defines an object to contain the new values to insert
+ContentValues mNewValues = new ContentValues();
+
+/*
+ * Sets the values of each column and inserts the word. The arguments to the "put"
+ * method are "column name" and "value"
+ */
+mNewValues.put(UserDictionary.Words.APP_ID, "example.user");
+mNewValues.put(UserDictionary.Words.LOCALE, "en_US");
+mNewValues.put(UserDictionary.Words.WORD, "insert");
+mNewValues.put(UserDictionary.Words.FREQUENCY, "100");
+
+mNewUri = getContentResolver().insert(
+    UserDictionary.Word.CONTENT_URI,   // the user dictionary content URI
+    mNewValues                          // the values to insert
+);
+
    +

    + The data for the new row goes into a single {@link android.content.ContentValues} object, which + is similar in form to a one-row cursor. The columns in this object don't need to have the + same data type, and if you don't want to specify a value at all, you can set a column + to null using {@link android.content.ContentValues#putNull(String) + ContentValues.putNull()}. +

    +

    + The snippet doesn't add the _ID column, because this column is maintained + automatically. The provider assigns a unique value of _ID to every row that is + added. Providers usually use this value as the table's primary key. +

    +

    + The content URI returned in newUri identifies the newly-added row, with + the following format: +

    +
    +content://user_dictionary/words/<id_value>
+
    +

    + The <id_value> is the contents of _ID for the new row. + Most providers can detect this form of content URI automatically and then perform the requested + operation on that particular row. +

    +

    + To get the value of _ID from the returned {@link android.net.Uri}, call + {@link android.content.ContentUris#parseId(Uri) ContentUris.parseId()}. +

    +

    Updating data

    +

    + To update a row, you use a {@link android.content.ContentValues} object with the updated + values just as you do with an insertion, and selection criteria just as you do with a query. + The client method you use is + {@link android.content.ContentResolver#update(Uri, ContentValues, String, String[]) + ContentResolver.update()}. You only need to add values to the + {@link android.content.ContentValues} object for columns you're updating. If you want to clear + the contents of a column, set the value to null. +

    +

    + The following snippet changes all the rows whose locale has the language "en" to a + have a locale of null. The return value is the number of rows that were updated: +

    +
    +// Defines an object to contain the updated values
+ContentValues mUpdateValues = new ContentValues();
+
+// Defines selection criteria for the rows you want to update
+String mSelectionClause = UserDictionary.Words.LOCALE +  "LIKE ?";
+String[] mSelectionArgs = {"en_%"};
+
+// Defines a variable to contain the number of updated rows
+int mRowsUpdated = 0;
+
+...
+
+/*
+ * Sets the updated value and updates the selected words.
+ */
+mUpdateValues.putNull(UserDictionary.Words.LOCALE);
+
+mRowsUpdated = getContentResolver().update(
+    UserDictionary.Words.CONTENT_URI,   // the user dictionary content URI
+    mUpdateValues                       // the columns to update
+    mSelectionClause                    // the column to select on
+    mSelectionArgs                      // the value to compare to
+);
+
    +

    + You should also sanitize user input when you call + {@link android.content.ContentResolver#update(Uri, ContentValues, String, String[]) + ContentResolver.update()}. To learn more about this, read the section + Protecting against malicious input. +

    +

    Deleting data

    +

    + Deleting rows is similar to retrieving row data: you specify selection criteria for the rows + you want to delete and the client method returns the number of deleted rows. + The following snippet deletes rows whose appid matches "user". The method returns the + number of deleted rows. +

    +
    +
+// Defines selection criteria for the rows you want to delete
+String mSelectionClause = UserDictionary.Words.APP_ID + " LIKE ?";
+String[] mSelectionArgs = {"user"};
+
+// Defines a variable to contain the number of rows deleted
+int mRowsDeleted = 0;
+
+...
+
+// Deletes the words that match the selection criteria
+mRowsDeleted = getContentResolver().delete(
+    UserDictionary.Words.CONTENT_URI,   // the user dictionary content URI
+    mSelectionClause                    // the column to select on
+    mSelectionArgs                      // the value to compare to
+);
+
    +

    + You should also sanitize user input when you call + {@link android.content.ContentResolver#delete(Uri, String, String[]) + ContentResolver.delete()}. To learn more about this, read the section + Protecting against malicious input. +

    + +

    Provider Data Types

    +

    + Content providers can offer many different data types. The User Dictionary Provider offers only + text, but providers can also offer the following formats: +

    + +

    + Another data type that providers often use is Binary Large OBject (BLOB) implemented as a + 64KB byte array. You can see the available data types by looking at the + {@link android.database.Cursor} class "get" methods. +

    +

    + The data type for each column in a provider is usually listed in its documentation. + The data types for the User Dictionary Provider are listed in the reference documentation + for its contract class {@link android.provider.UserDictionary.Words} (contract classes are + described in the section Contract Classes). + You can also determine the data type by calling {@link android.database.Cursor#getType(int) + Cursor.getType()}. +

    +

    + Providers also maintain MIME data type information for each content URI they define. You can + use the MIME type information to find out if your application can handle data that the + provider offers, or to choose a type of handling based on the MIME type. You usually need the + MIME type when you are working with a provider that contains complex + data structures or files. For example, the {@link android.provider.ContactsContract.Data} + table in the Contacts Provider uses MIME types to label the type of contact data stored in each + row. To get the MIME type corresponding to a content URI, call + {@link android.content.ContentResolver#getType(Uri) ContentResolver.getType()}. +

    +

    + The section MIME Type Reference describes the + syntax of both standard and custom MIME types. +

    + + + +

    Alternative Forms of Provider Access

    +

    + Three alternative forms of provider access are important in application development: +

    + +

    + Batch access and modification via intents are described in the following sections. +

    +

    Batch access

    +

    + Batch access to a provider is useful for inserting a large number of rows, or for inserting + rows in multiple tables in the same method call, or in general for performing a set of + operations across process boundaries as a transaction (an atomic operation). +

    +

    + To access a provider in "batch mode", + you create an array of {@link android.content.ContentProviderOperation} objects and then + dispatch them to a content provider with + {@link android.content.ContentResolver#applyBatch(String, ArrayList) + ContentResolver.applyBatch()}. You pass the content provider's authority to this + method, rather than a particular content URI, which allows each + {@link android.content.ContentProviderOperation} object in the array to work against a + different table. A call to {@link android.content.ContentResolver#applyBatch(String, ArrayList) + ContentResolver.applyBatch()} returns an array of results. +

    +

    + The description of the {@link android.provider.ContactsContract.RawContacts} contract class + includes a code snippet that demonstrates batch insertion. The + Contact Manager + sample application contains an example of batch access in its ContactAdder.java + source file. +

    +
    +
    +

    Displaying data using a helper app

    +

    + If your application does have access permissions, you still may want to use an + intent to display data in another application. For example, the Calendar application accepts an + {@link android.content.Intent#ACTION_VIEW} intent, which displays a particular date or event. + This allows you to display calendar information without having to create your own UI. + To learn more about this feature, see the + Calendar Provider guide. +

    +

    + The application to which you send the intent doesn't have to be the application + associated with the provider. For example, you can retrieve a contact from the + Contact Provider, then send an {@link android.content.Intent#ACTION_VIEW} intent + containing the content URI for the contact's image to an image viewer. +

    +
    +
    +

    Data access via intents

    +

    + Intents can provide indirect access to a content provider. You allow the user to access + data in a provider even if your application doesn't have access permissions, either by + getting a result intent back from an application that has permissions, or by activating an + application that has permissions and letting the user do work in it. +

    +

    Getting access with temporary permissions

    +

    + You can access data in a content provider, even if you don't have the proper access + permissions, by sending an intent to an application that does have the permissions and + receiving back a result intent containing "URI" permissions. + These are permissions for a specific content URI that last until the activity that receives + them is finished. The application that has permanent permissions grants temporary + permissions by setting a flag in the result intent: +

    + +

    + Note: These flags don't give general read or write access to the provider + whose authority is contained in the content URI. The access is only for the URI itself. +

    +

    + A provider defines URI permissions for content URIs in its manifest, using the + + android:grantUriPermission + attribute of the + {@code <provider>} + element, as well as the + {@code + <grant-uri-permission>} child element of the + {@code <provider>} + element. The URI permissions mechanism is explained in more detail in the + Security and Permissions guide, + in the section "URI Permissions". +

    +

    + For example, you can retrieve data for a contact in the Contacts Provider, even if you don't + have the {@link android.Manifest.permission#READ_CONTACTS} permission. You might want to do + this in an application that sends e-greetings to a contact on his or her birthday. Instead of + requesting {@link android.Manifest.permission#READ_CONTACTS}, which gives you access to all of + the user's contacts and all of their information, you prefer to let the user control which + contacts are used by your application. To do this, you use the following process: +

    +
      +
    1. + Your application sends an intent containing the action + {@link android.content.Intent#ACTION_PICK} and the "contacts" MIME type + {@link android.provider.ContactsContract.RawContacts#CONTENT_ITEM_TYPE}, using the + method {@link android.app.Activity#startActivityForResult(Intent, int) + startActivityForResult()}. +
      2. +
    2. + Because this intent matches the intent filter for the + People app's "selection" activity, the activity will come to the foreground. +
      3. +
    3. + In the selection activity, the user selects a + contact to update. When this happens, the selection activity calls + {@link android.app.Activity#setResult(int, Intent) setResult(resultcode, intent)} + to set up a intent to give back to your application. The intent contains the content URI + of the contact the user selected, and the "extras" flags + {@link android.content.Intent#FLAG_GRANT_READ_URI_PERMISSION}. These flags grant URI + permission to your app to read data for the contact pointed to by the + content URI. The selection activity then calls {@link android.app.Activity#finish()} to + return control to your application. +
      4. +
    4. + Your activity returns to the foreground, and the system calls your activity's + {@link android.app.Activity#onActivityResult(int, int, Intent) onActivityResult()} + method. This method receives the result intent created by the selection activity in + the People app. +
      5. +
    5. + With the content URI from the result intent, you can read the contact's data + from the Contacts Provider, even though you didn't request permanent read access permission + to the provider in your manifest. You can then get the contact's birthday information + or his or her email address and then send the e-greeting. +
      6. +
    +

    Using another application

    +

    + A simple way to allow the user to modify data to which you don't have access permissions is to + activate an application that has permissions and let the user do the work there. +

    +

    + For example, the Calendar application accepts an + {@link android.content.Intent#ACTION_INSERT} intent, which allows you to activate the + application's insert UI. You can pass "extras" data in this intent, which the application + uses to pre-populate the UI. Because recurring events have a complex syntax, the preferred + way of inserting events into the Calendar Provider is to activate the Calendar app with an + {@link android.content.Intent#ACTION_INSERT} and then let the user insert the event there. +

    + +

    Contract Classes

    +

    + A contract class defines constants that help applications work with the content URIs, column + names, intent actions, and other features of a content provider. Contract classes are not + included automatically with a provider; the provider's developer has to define them and then + make them available to other developers. Many of the providers included with the Android + platform have corresponding contract classes in the package {@link android.provider}. +

    +

    + For example, the User Dictionary Provider has a contract class + {@link android.provider.UserDictionary} containing content URI and column name constants. The + content URI for the "words" table is defined in the constant + {@link android.provider.UserDictionary.Words#CONTENT_URI UserDictionary.Words.CONTENT_URI}. + The {@link android.provider.UserDictionary.Words} class also contains column name constants, + which are used in the example snippets in this guide. For example, a query projection can be + defined as: +

    +
    +String[] mProjection =
+{
+    UserDictionary.Words._ID,
+    UserDictionary.Words.WORD,
+    UserDictionary.Words.LOCALE
+};
+
    +

    + Another contract class is {@link android.provider.ContactsContract} for the Contacts Provider. + The reference documentation for this class includes example code snippets. One of its + subclasses, {@link android.provider.ContactsContract.Intents.Insert}, is a contract + class that contains constants for intents and intent data. +

    + + + +

    MIME Type Reference

    +

    + Content providers can return standard MIME media types, or custom MIME type strings, or both. +

    +

    + MIME types have the format +

    +
    +type/subtype
+
    +

    + For example, the well-known MIME type text/html has the text type and + the html subtype. If the provider returns this type for a URI, it means that a + query using that URI will return text containing HTML tags. +

    +

    + Custom MIME type strings, also called "vendor-specific" MIME types, have more + complex type and subtype values. The type value is always +

    +
    +vnd.android.cursor.dir
+
    +

    + for multiple rows, or +

    +
    +vnd.android.cursor.item
+
    +

    + for a single row. +

    +

    + The subtype is provider-specific. The Android built-in providers usually have a simple + subtype. For example, the when the Contacts application creates a row for a telephone number, + it sets the following MIME type in the row: +

    +
    +vnd.android.cursor.item/phone_v2
+
    +

    + Notice that the subtype value is simply phone_v2. +

    +

    + Other provider developers may create their own pattern of subtypes based on the provider's + authority and table names. For example, consider a provider that contains train timetables. + The provider's authority is com.example.trains, and it contains the tables + Line1, Line2, and Line3. In response to the content URI +

    +

    +

    +content://com.example.trains/Line1
+
    +

    + for table Line1, the provider returns the MIME type +

    +
    +vnd.android.cursor.dir/vnd.example.line1
+
    +

    + In response to the content URI +

    +
    +content://com.example.trains/Line2/5
+
    +

    + for row 5 in table Line2, the provider returns the MIME type +

    +
    +vnd.android.cursor.item/vnd.example.line2
+
    +

    + Most content providers define contract class constants for the MIME types they use. The + Contacts Provider contract class {@link android.provider.ContactsContract.RawContacts}, + for example, defines the constant + {@link android.provider.ContactsContract.RawContacts#CONTENT_ITEM_TYPE} for the MIME type of + a single raw contact row. +

    +

    + Content URIs for single rows are described in the section + Content URIs. +

    diff --git a/docs/html/guide/topics/providers/content-provider-creating.jd b/docs/html/guide/topics/providers/content-provider-creating.jd new file mode 100644 index 000000000000..4ebdb502138c --- /dev/null +++ b/docs/html/guide/topics/providers/content-provider-creating.jd @@ -0,0 +1,1215 @@ +page.title=Creating a Content Provider +@jd:body + + + +

    + A content provider manages access to a central repository of data. You implement a + provider as one or more classes in an Android application, along with elements in + the manifest file. One of your classes implements a subclass + {@link android.content.ContentProvider}, which is the interface between your provider and + other applications. Although content providers are meant to make data available to other + applications, you may of course have activities in your application that allow the user + to query and modify the data managed by your provider. +

    +

    + The rest of this topic is a basic list of steps for building a content provider and a list + of APIs to use. +

    + + + +

    Before You Start Building

    +

    + Before you start building a provider, do the following: +

    +
      +
    1. + Decide if you need a content provider. You need to build a content + provider if you want to provide one or more of the following features: +
        +
      • You want to offer complex data or files to other applications.
        • +
      • You want to allow users to copy complex data from your app into other apps.
        • +
      • You want to provide custom search suggestions using the search framework.
        • +
      +

      + You don't need a provider to use an SQLite database if the use is entirely within + your own application. +

      +
      2. +
    2. + If you haven't done so already, read the topic + + Content Provider Basics to learn more about providers. +
      3. +
    +

    + Next, follow these steps to build your provider: +

    +
      +
    1. + Design the raw storage for your data. A content provider offers data in two ways: +
      +
      + File data +
      +
      + Data that normally goes into files, such as + photos, audio, or videos. Store the files in your application's private + space. In response to a request for a file from another application, your + provider can offer a handle to the file. +
      +
      + "Structured" data +
      +
      + Data that normally goes into a database, array, or similar structure. + Store the data in a form that's compatible with tables of rows and columns. A row + represents an entity, such as a person or an item in inventory. A column represents + some data for the entity, such a person's name or an item's price. A common way to + store this type of data is in an SQLite database, but you can use any type of + persistent storage. To learn more about the storage types available in the + Android system, see the section + Designing Data Storage. +
      +
      +
      2. +
    2. + Define a concrete implementation of the {@link android.content.ContentProvider} class and + its required methods. This class is the interface between your data and the rest of the + Android system. For more information about this class, see the section + Implementing the ContentProvider Class. +
      3. +
    3. + Define the provider's authority string, its content URIs, and column names. If you want + the provider's application to handle intents, also define intent actions, extras data, + and flags. Also define the permissions that you will require for applications that want + to access your data. You should consider defining all of these values as constants in a + separate contract class; later, you can expose this class to other developers. For more + information about content URIs, see the + section Designing Content URIs. + For more information about intents, see the + section Intents and Data Access. +
      4. +
    4. + Add other optional pieces, such as sample data or an implementation + of {@link android.content.AbstractThreadedSyncAdapter} that can synchronize data between + the provider and cloud-based data. +
      5. +
    + + + +

    Designing Data Storage

    +

    + A content provider is the interface to data saved in a structured format. Before you create + the interface, you must decide how to store the data. You can store the data in any form you + like, and then design the interface to read and write the data as necessary. +

    +

    + These are some of the data storage technologies that are available in Android: +

    + +

    + Data design considerations +

    +

    + Here are some tips for designing your provider's data structure: +

    + + +

    Designing Content URIs

    +

    + A content URI is a URI that identifies data in a provider. Content URIs include + the symbolic name of the entire provider (its authority) and a + name that points to a table or file (a path). The optional id part points to + an individual row in a table. Every data access method of + {@link android.content.ContentProvider} has a content URI as an argument; this allows you to + determine the table, row, or file to access. +

    +

    + The basics of content URIs are described in the topic + + Content Provider Basics. +

    +

    Designing an authority

    +

    + A provider usually has a single authority, which serves as its Android-internal name. To + avoid conflicts with other providers, you should use Internet domain ownership (in reverse) + as the basis of your provider authority. Because this recommendation is also true for Android + package names, you can define your provider authority as an extension of the name + of the package containing the provider. For example, if your Android package name is + com.example.<appname>, you should give your provider the + authority com.example.<appname>.provider. +

    +

    Designing a path structure

    +

    + Developers usually create content URIs from the authority by appending paths that point to + individual tables. For example, if you have two tables table1 and + table2, you combine the authority from the previous example to yield the + content URIs + com.example.<appname>.provider/table1 and + com.example.<appname>.provider/table2. Paths aren't + limited to a single segment, and there doesn't have to be a table for each level of the path. +

    +

    Handling content URI IDs

    +

    + By convention, providers offer access to a single row in a table by accepting a content URI + with an ID value for the row at the end of the URI. Also by convention, providers match the + ID value to the table's _ID column, and perform the requested access against the + row that matches. +

    +

    + This convention facilitates a common design pattern for apps accessing a provider. The app + does a query against the provider and displays the resulting {@link android.database.Cursor} + in a {@link android.widget.ListView} using a {@link android.widget.CursorAdapter}. + The definition of {@link android.widget.CursorAdapter} requires one of the columns in the + {@link android.database.Cursor} to be _ID +

    +

    + The user then picks one of the displayed rows from the UI in order to look at or modify the + data. The app gets the corresponding row from the {@link android.database.Cursor} backing the + {@link android.widget.ListView}, gets the _ID value for this row, appends it to + the content URI, and sends the access request to the provider. The provider can then do the + query or modification against the exact row the user picked. +

    +

    Content URI patterns

    +

    + To help you choose which action to take for an incoming content URI, the provider API includes + the convenience class {@link android.content.UriMatcher}, which maps content URI "patterns" to + integer values. You can use the integer values in a switch statement that + chooses the desired action for the content URI or URIs that match a particular pattern. +

    +

    + A content URI pattern matches content URIs using wildcard characters: +

    + +

    + As an example of designing and coding content URI handling, consider a provider with the + authority com.example.app.provider that recognizes the following content URIs + pointing to tables: +

    + +

    + The provider also recognizes these content URIs if they have a row ID appended to them, as + for example content://com.example.app.provider/table3/1 for the row identified by + 1 in table3. +

    +

    + The following content URI patterns would be possible: +

    +
    +
    + content://com.example.app.provider/* +
    +
    + Matches any content URI in the provider. +
    +
    + content://com.example.app.provider/table2/*: +
    +
    + Matches a content URI for the tables dataset1 + and dataset2, but doesn't match content URIs for table1 or + table3. +
    +
    + content://com.example.app.provider/table3/#: Matches a content URI + for single rows in table3, such as + content://com.example.app.provider/table3/6 for the row identified by + 6. +
    +
    +

    + The following code snippet shows how the methods in {@link android.content.UriMatcher} work. + This code handles URIs for an entire table differently from URIs for a + single row, by using the content URI pattern + content://<authority>/<path> for tables, and + content://<authority>/<path>/<id> for single rows. +

    +

    + The method {@link android.content.UriMatcher#addURI(String, String, int) addURI()} maps an + authority and path to an integer value. The method android.content.UriMatcher#match(Uri) + match()} returns the integer value for a URI. A switch statement + chooses between querying the entire table, and querying for a single record: +

    +
    +public class ExampleProvider extends ContentProvider {
+...
+    // Creates a UriMatcher object.
+    private static final UriMatcher sUriMatcher;
+...
+    /*
+     * The calls to addURI() go here, for all of the content URI patterns that the provider
+     * should recognize. For this snippet, only the calls for table 3 are shown.
+     */
+...
+    /*
+     * Sets the integer value for multiple rows in table 3 to 1. Notice that no wildcard is used
+     * in the path
+     */
+    sUriMatcher.addURI("com.example.app.provider", "table3", 1);
+
+    /*
+     * Sets the code for a single row to 2. In this case, the "#" wildcard is
+     * used. "content://com.example.app.provider/table3/3" matches, but
+     * "content://com.example.app.provider/table3 doesn't.
+     */
+    sUriMatcher.addURI("com.example.app.provider", "table3/#", 2);
+...
+    // Implements ContentProvider.query()
+    public Cursor query(
+        Uri uri,
+        String[] projection,
+        String selection,
+        String[] selectionArgs,
+        String sortOrder) {
+...
+        /*
+         * Choose the table to query and a sort order based on the code returned for the incoming
+         * URI. Here, too, only the statements for table 3 are shown.
+         */
+        switch (sUriMatcher.match(uri)) {
+
+
+            // If the incoming URI was for all of table3
+            case 1:
+
+                if (TextUtils.isEmpty(sortOrder)) sortOrder = "_ID ASC";
+                break;
+
+            // If the incoming URI was for a single row
+            case 2:
+
+                /*
+                 * Because this URI was for a single row, the _ID value part is
+                 * present. Get the last path segment from the URI; this is the _ID value.
+                 * Then, append the value to the WHERE clause for the query
+                 */
+                selection = selection + "_ID = " uri.getLastPathSegment();
+                break;
+
+            default:
+            ...
+                // If the URI is not recognized, you should do some error handling here.
+        }
+        // call the code to actually do the query
+    }
+
    +

    + Another class, {@link android.content.ContentUris}, provides convenience methods for working + with the id part of content URIs. The classes {@link android.net.Uri} and + {@link android.net.Uri.Builder} include convenience methods for parsing existing + {@link android.net.Uri} objects and building new ones. +

    + + +

    Implementing the ContentProvider Class

    +

    + The {@link android.content.ContentProvider} instance manages access + to a structured set of data by handling requests from other applications. All forms + of access eventually call {@link android.content.ContentResolver}, which then calls a concrete + method of {@link android.content.ContentProvider} to get access. +

    +

    Required methods

    +

    + The abstract class {@link android.content.ContentProvider} defines six abstract methods that + you must implement as part of your own concrete subclass. All of these methods except + {@link android.content.ContentProvider#onCreate() onCreate()} are called by a client application + that is attempting to access your content provider: +

    +
    +
    + {@link android.content.ContentProvider#query(Uri, String[], String, String[], String) + query()} +
    +
    + Retrieve data from your provider. Use the arguments to select the table to + query, the rows and columns to return, and the sort order of the result. + Return the data as a {@link android.database.Cursor} object. +
    +
    + {@link android.content.ContentProvider#insert(Uri, ContentValues) insert()} +
    +
    + Insert a new row into your provider. Use the arguments to select the + destination table and to get the column values to use. Return a content URI for the + newly-inserted row. +
    +
    + {@link android.content.ContentProvider#update(Uri, ContentValues, String, String[]) + update()} +
    +
    + Update existing rows in your provider. Use the arguments to select the table and rows + to update and to get the updated column values. Return the number of rows updated. +
    +
    + {@link android.content.ContentProvider#delete(Uri, String, String[]) delete()} +
    +
    + Delete rows from your provider. Use the arguments to select the table and the rows to + delete. Return the number of rows deleted. +
    +
    + {@link android.content.ContentProvider#getType(Uri) getType()} +
    +
    + Return the MIME type corresponding to a content URI. This method is described in more + detail in the section Implementing Content Provider MIME Types. +
    +
    + {@link android.content.ContentProvider#onCreate() onCreate()} +
    +
    + Initialize your provider. The Android system calls this method immediately after it + creates your provider. Notice that your provider is not created until a + {@link android.content.ContentResolver} object tries to access it. +
    +
    +

    + Notice that these methods have the same signature as the identically-named + {@link android.content.ContentResolver} methods. +

    +

    + Your implementation of these methods should account for the following: +

    + +

    Implementing the query() method

    +

    + The + {@link android.content.ContentProvider#query(Uri, String[], String, String[], String) + ContentProvider.query()} method must return a {@link android.database.Cursor} object, or if it + fails, throw an {@link java.lang.Exception}. If you are using an SQLite database as your data + storage, you can simply return the {@link android.database.Cursor} returned by one of the + query() methods of the {@link android.database.sqlite.SQLiteDatabase} class. + If the query does not match any rows, you should return a {@link android.database.Cursor} + instance whose {@link android.database.Cursor#getCount()} method returns 0. + You should return null only if an internal error occurred during the query process. +

    +

    + If you aren't using an SQLite database as your data storage, use one of the concrete subclasses + of {@link android.database.Cursor}. For example, the {@link android.database.MatrixCursor} class + implements a cursor in which each row is an array of {@link java.lang.Object}. With this class, + use {@link android.database.MatrixCursor#addRow(Object[]) addRow()} to add a new row. +

    +

    + Remember that the Android system must be able to communicate the {@link java.lang.Exception} + across process boundaries. Android can do this for the following exceptions that may be useful + in handling query errors: +

    + +

    Implementing the insert() method

    +

    + The {@link android.content.ContentProvider#insert(Uri, ContentValues) insert()} method adds a + new row to the appropriate table, using the values in the {@link android.content.ContentValues} + argument. If a column name is not in the {@link android.content.ContentValues} argument, you + may want to provide a default value for it either in your provider code or in your database + schema. +

    +

    + This method should return the content URI for the new row. To construct this, append the new + row's _ID (or other primary key) value to the table's content URI, using + {@link android.content.ContentUris#withAppendedId(Uri, long) withAppendedId()}. +

    +

    Implementing the delete() method

    +

    + The {@link android.content.ContentProvider#delete(Uri, String, String[]) delete()} method + does not have to physically delete rows from your data storage. If you are using a sync adapter + with your provider, you should consider marking a deleted row + with a "delete" flag rather than removing the row entirely. The sync adapter can + check for deleted rows and remove them from the server before deleting them from the provider. +

    +

    Implementing the update() method

    +

    + The {@link android.content.ContentProvider#update(Uri, ContentValues, String, String[]) + update()} method takes the same {@link android.content.ContentValues} argument used by + {@link android.content.ContentProvider#insert(Uri, ContentValues) insert()}, and the + same selection and selectionArgs arguments used by + {@link android.content.ContentProvider#delete(Uri, String, String[]) delete()} and + {@link android.content.ContentProvider#query(Uri, String[], String, String[], String) + ContentProvider.query()}. This may allow you to re-use code between these methods. +

    +

    Implementing the onCreate() method

    +

    + The Android system calls {@link android.content.ContentProvider#onCreate() + onCreate()} when it starts up the provider. You should perform only fast-running initialization + tasks in this method, and defer database creation and data loading until the provider actually + receives a request for the data. If you do lengthy tasks in + {@link android.content.ContentProvider#onCreate() onCreate()}, you will slow down your + provider's startup. In turn, this will slow down the response from the provider to other + applications. +

    +

    + For example, if you are using an SQLite database you can create + a new {@link android.database.sqlite.SQLiteOpenHelper} object in + {@link android.content.ContentProvider#onCreate() ContentProvider.onCreate()}, + and then create the SQL tables the first time you open the database. To facilitate this, the + first time you call {@link android.database.sqlite.SQLiteOpenHelper#getWritableDatabase + getWritableDatabase()}, it automatically calls the + {@link android.database.sqlite.SQLiteOpenHelper#onCreate(SQLiteDatabase) + SQLiteOpenHelper.onCreate()} method. +

    +

    + The following two snippets demonstrate the interaction between + {@link android.content.ContentProvider#onCreate() ContentProvider.onCreate()} and + {@link android.database.sqlite.SQLiteOpenHelper#onCreate(SQLiteDatabase) + SQLiteOpenHelper.onCreate()}. The first snippet is the implementation of + {@link android.content.ContentProvider#onCreate() ContentProvider.onCreate()}: +

    +
    +public class ExampleProvider extends ContentProvider
+
+    /*
+     * Defines a handle to the database helper object. The MainDatabaseHelper class is defined
+     * in a following snippet.
+     */
+    private MainDatabaseHelper mOpenHelper;
+
+    // Defines the database name
+    private static final String DBNAME = "mydb";
+
+    // Holds the database object
+    private SQLiteDatabase db;
+
+    public boolean onCreate() {
+
+        /*
+         * Creates a new helper object. This method always returns quickly.
+         * Notice that the database itself isn't created or opened
+         * until SQLiteOpenHelper.getWritableDatabase is called
+         */
+        mOpenHelper = new SQLiteOpenHelper(
+            getContext(),        // the application context
+            DBNAME,              // the name of the database)
+            null,                // uses the default SQLite cursor
+            1                    // the version number
+        );
+
+        return true;
+    }
+
+    ...
+
+    // Implements the provider's insert method
+    public Cursor insert(Uri uri, ContentValues values) {
+        // Insert code here to determine which table to open, handle error-checking, and so forth
+
+        ...
+
+        /*
+         * Gets a writeable database. This will trigger its creation if it doesn't already exist.
+         *
+         */
+        db = mOpenHelper.getWritableDatabase();
+    }
+}
+
    +

    + The next snippet is the implementation of + {@link android.database.sqlite.SQLiteOpenHelper#onCreate(SQLiteDatabase) + SQLiteOpenHelper.onCreate()}, including a helper class: +

    +
    +...
+// A string that defines the SQL statement for creating a table
+private static final String SQL_CREATE_MAIN = "CREATE TABLE " +
+    "main " +                       // Table's name
+    "(" +                           // The columns in the table
+    " _ID INTEGER PRIMARY KEY, " +
+    " WORD TEXT"
+    " FREQUENCY INTEGER " +
+    " LOCALE TEXT )";
+...
+/**
+ * Helper class that actually creates and manages the provider's underlying data repository.
+ */
+protected static final class MainDatabaseHelper extends SQLiteOpenHelper {
+
+    /*
+     * Instantiates an open helper for the provider's SQLite data repository
+     * Do not do database creation and upgrade here.
+     */
+    MainDatabaseHelper(Context context) {
+        super(context, DBNAME, null, 1);
+    }
+
+    /*
+     * Creates the data repository. This is called when the provider attempts to open the
+     * repository and SQLite reports that it doesn't exist.
+     */
+    public void onCreate(SQLiteDatabase db) {
+
+        // Creates the main table
+        db.execSQL(SQL_CREATE_MAIN);
+    }
+}
+
    + + + +

    Implementing ContentProvider MIME Types

    +

    + The {@link android.content.ContentProvider} class has two methods for returning MIME types: +

    +
    +
    + {@link android.content.ContentProvider#getType(Uri) getType()} +
    +
    + One of the required methods that you must implement for any provider. +
    +
    + {@link android.content.ContentProvider#getStreamTypes(Uri, String) getStreamTypes()} +
    +
    + A method that you're expected to implement if your provider offers files. +
    +
    +

    MIME types for tables

    +

    + The {@link android.content.ContentProvider#getType(Uri) getType()} method returns a + {@link java.lang.String} in MIME format that describes the type of data returned by the content + URI argument. The {@link android.net.Uri} argument can be a pattern rather than a specific URI; + in this case, you should return the type of data associated with content URIs that match the + pattern. +

    +

    + For common types of data such as as text, HTML, or JPEG, + {@link android.content.ContentProvider#getType(Uri) getType()} should return the standard + MIME type for that data. A full list of these standard types is available on the + IANA MIME Media Types + website. +

    +

    + For content URIs that point to a row or rows of table data, + {@link android.content.ContentProvider#getType(Uri) getType()} should return + a MIME type in Android's vendor-specific MIME format: +

    + +

    + For example, if a provider's authority is + com.example.app.provider, and it exposes a table named + table1, the MIME type for multiple rows in table1 is: +

    +
    +vnd.android.cursor.dir/vnd.com.example.provider.table1
+
    +

    + For a single row of table1, the MIME type is: +

    +
    +vnd.android.cursor.item/vnd.com.example.provider.table1
+
    +

    MIME types for files

    +

    + If your provider offers files, implement + {@link android.content.ContentProvider#getStreamTypes(Uri, String) getStreamTypes()}. + The method returns a {@link java.lang.String} array of MIME types for the files your provider + can return for a given content URI. You should filter the MIME types you offer by the MIME type + filter argument, so that you return only those MIME types that the client wants to handle. +

    +

    + For example, consider a provider that offers photo images as files in .jpg, + .png, and .gif format. + If an application calls {@link android.content.ContentResolver#getStreamTypes(Uri, String) + ContentResolver.getStreamTypes()} with the filter string image/* (something that + is an "image"), + then the {@link android.content.ContentProvider#getStreamTypes(Uri, String) + ContentProvider.getStreamTypes()} method should return the array: +

    +
    +{ "image/jpeg", "image/png", "image/gif"}
+
    +

    + If the app is only interested in .jpg files, then it can call + {@link android.content.ContentResolver#getStreamTypes(Uri, String) + ContentResolver.getStreamTypes()} with the filter string *\/jpeg, and + {@link android.content.ContentProvider#getStreamTypes(Uri, String) + ContentProvider.getStreamTypes()} should return: +

    +{"image/jpeg"}
+
    +

    + If your provider doesn't offer any of the MIME types requested in the filter string, + {@link android.content.ContentProvider#getStreamTypes(Uri, String) getStreamTypes()} + should return null. +

    + + + +

    Implementing a Contract Class

    +

    + A contract class is a public final class that contains constant definitions for the + URIs, column names, MIME types, and other meta-data that pertain to the provider. The class + establishes a contract between the provider and other applications by ensuring that the provider + can be correctly accessed even if there are changes to the actual values of URIs, column names, + and so forth. +

    +

    + A contract class also helps developers because it usually has mnemonic names for its constants, + so developers are less likely to use incorrect values for column names or URIs. Since it's a + class, it can contain Javadoc documentation. Integrated development environments such as + Eclipse can auto-complete constant names from the contract class and display Javadoc for the + constants. +

    +

    + Developers can't access the contract class's class file from your application, but they can + statically compile it into their application from a .jar file you provide. +

    +

    + The {@link android.provider.ContactsContract} class and its nested classes are examples of + contract classes. +

    +

    Implementing Content Provider Permissions

    +

    + Permissions and access for all aspects of the Android system are described in detail in the + topic Security and Permissions. + The topic Data Storage also + described the security and permissions in effect for various types of storage. + In brief, the important points are: +

    + +

    + If you want to use content provider permissions to control access to your data, then you should + store your data in internal files, SQLite databases, or the "cloud" (for example, + on a remote server), and you should keep files and databases private to your application. +

    +

    Implementing permissions

    +

    + All applications can read from or write to your provider, even if the underlying data is + private, because by default your provider does not have permissions set. To change this, + set permissions for your provider in your manifest file, using attributes or child + elements of the + <provider> element. You can set permissions that apply to the entire provider, + or to certain tables, or even to certain records, or all three. +

    +

    + You define permissions for your provider with one or more + + <permission> elements in your manifest file. To make the + permission unique to your provider, use Java-style scoping for the + + android:name attribute. For example, name the read permission + com.example.app.provider.permission.READ_PROVIDER. + +

    +

    + The following list describes the scope of provider permissions, starting with the + permissions that apply to the entire provider and then becoming more fine-grained. + More fine-grained permissions take precedence over ones with larger scope: +

    +
    +
    + Single read-write provider-level permission +
    +
    + One permission that controls both read and write access to the entire provider, specified + with the + android:permission attribute of the + + <provider> element. +
    +
    + Separate read and write provider-level permission +
    +
    + A read permission and a write permission for the entire provider. You specify them + with the + android:readPermission and + + android:writePermission attributes of the + + <provider> element. They take precedence over the permission required by + + android:permission. +
    +
    + Path-level permission +
    +
    + Read, write, or read/write permission for a content URI in your provider. You specify + each URI you want to control with a + + <path-permission> child element of the + + <provider> element. For each content URI you specify, you can specify a + read/write permission, a read permission, or a write permission, or all three. The read and + write permissions take precedence over the read/write permission. Also, path-level + permission takes precedence over provider-level permissions. +
    +
    + Temporary permission +
    +
    + A permission level that grants temporary access to an application, even if the application + doesn't have the permissions that are normally required. The temporary + access feature reduces the number of permissions an application has to request in + its manifest. When you turn on temporary permissions, the only applications that need + "permanent" permissions for your provider are ones that continually access all + your data. +

    + Consider the permissions you need to implement an email provider and app, when you + want to allow an outside image viewer application to display photo attachments from your + provider. To give the image viewer the necessary access without requiring permissions, + set up temporary permissions for content URIs for photos. Design your email app so + that when the user wants to display a photo, the app sends an intent containing the + photo's content URI and permission flags to the image viewer. The image viewer can + then query your email provider to retrieve the photo, even though the viewer doesn't + have the normal read permission for your provider. +

    +

    + To turn on temporary permissions, either set the + + android:grantUriPermissions attribute of the + + <provider> element, or add one or more + + <grant-uri-permission> child elements to your + + <provider> element. If you use temporary permissions, you have to call + {@link android.content.Context#revokeUriPermission(Uri, int) + Context.revokeUriPermission()} whenever you remove support for a content URI from your + provider, and the content URI is associated with a temporary permission. +

    +

    + The attribute's value determines how much of your provider is made accessible. + If the attribute is set to true, then the system will grant temporary + permission to your entire provider, overriding any other permissions that are required + by your provider-level or path-level permissions. +

    +

    + If this flag is set to false, then you must add + + <grant-uri-permission> child elements to your + + <provider> element. Each child element specifies the content URI or + URIs for which temporary access is granted. +

    +

    + To delegate temporary access to an application, an intent must contain + the {@link android.content.Intent#FLAG_GRANT_READ_URI_PERMISSION} or the + {@link android.content.Intent#FLAG_GRANT_WRITE_URI_PERMISSION} flags, or both. These + are set with the {@link android.content.Intent#setFlags(int) setFlags()} method. +

    +

    + If the + android:grantUriPermissions attribute is not present, it's assumed to be + false. +

    +
    +
    + + + + +

    The <provider> Element

    +

    + Like {@link android.app.Activity} and {@link android.app.Service} components, + a subclass of {@link android.content.ContentProvider} + must be defined in the manifest file for its application, using the + + <provider> element. The Android system gets the following information from + the element: +

    +
    + Authority + ({@code + android:authorities}) +
    +
    + Symbolic names that identify the entire provider within the system. This + attribute is described in more detail in the section + Designing Content URIs. +
    +
    + Provider class name + ( +android:name + ) +
    +
    + The class that implements {@link android.content.ContentProvider}. This class is + described in more detail in the section + Implementing the ContentProvider Class. +
    +
    + Permissions +
    +
    + Attributes that specify the permissions that other applications must have in order to access + the provider's data: + +

    + Permissions and their corresponding attributes are described in more + detail in the section + Implementing Content Provider Permissions. +

    +
    +
    + Startup and control attributes +
    +
    + These attributes determine how and when the Android system starts the provider, the + process characteristics of the provider, and other run-time settings: +
      +
    • + + android:enabled: Flag allowing the system to start the provider. +
      • +
    • + + android:exported: Flag allowing other applications to use this provider. +
      • +
    • + + android:initOrder: The order in which this provider should be started, + relative to other providers in the same process. +
      • +
    • + + android:multiProcess: Flag allowing the system to start the provider + in the same process as the calling client. +
      • +
    • + + android:process: The name of the process in which the provider should + run. +
      • +
    • + + android:syncable: Flag indicating that the provider's data is to be + sync'ed with data on a server. +
      • +
    +

    + The attributes are fully documented in the dev guide topic for the + + <provider> + element. +

    +
    +
    + Informational attributes +
    +
    + An optional icon and label for the provider: +
      +
    • + + android:icon: A drawable resource containing an icon for the provider. + The icon appears next to the provider's label in the list of apps in + Settings > Apps > All. +
      • +
    • + + android:label: An informational label describing the provider or its + data, or both. The label appears in the list of apps in + Settings > Apps > All. +
      • +
    +

    + The attributes are fully documented in the dev guide topic for the + + <provider> element. +

    +
    +
    + + +

    Intents and Data Access

    +

    + Applications can access a content provider indirectly with an {@link android.content.Intent}. + The application does not call any of the methods of {@link android.content.ContentResolver} or + {@link android.content.ContentProvider}. Instead, it sends an intent that starts an activity, + which is often part of the provider's own application. The destination activity is in charge of + retrieving and displaying the data in its UI. Depending on the action in the intent, the + destination activity may also prompt the user to make modifications to the provider's data. + An intent may also contain "extras" data that the destination activity displays + in the UI; the user then has the option of changing this data before using it to modify the + data in the provider. +

    +

    + +

    +

    + You may want to use intent access to help ensure data integrity. Your provider may depend + on having data inserted, updated, and deleted according to strictly defined business logic. If + this is the case, allowing other applications to directly modify your data may lead to + invalid data. If you want developers to use intent access, be sure to document it thoroughly. + Explain to them why intent access using your own application's UI is better than trying to + modify the data with their code. +

    +

    + Handling an incoming intent that wishes to modify your provider's data is no different from + handling other intents. You can learn more about using intents by reading the topic + Intents and Intent Filters. +

    diff --git a/docs/html/guide/topics/providers/content-providers.jd b/docs/html/guide/topics/providers/content-providers.jd index 95331ce38519..1707f038b3ce 100644 --- a/docs/html/guide/topics/providers/content-providers.jd +++ b/docs/html/guide/topics/providers/content-providers.jd @@ -1,922 +1,96 @@ page.title=Content Providers @jd:body -
    -

    In this document

    -
      -
    1. Content provider basics
      2. -
    2. Querying a content provider
      3. -
    3. Modifying data in a provider
      4. -
    4. Creating a content provider
      5. -
    5. Content URI summary
      6. -
    -

    Key classes

    + +

    Topics

      -
    1. {@link android.content.ContentProvider}
      2. -
    2. {@link android.content.ContentResolver}
      3. -
    3. {@link android.database.Cursor}
      4. +
    4. + + Content Provider Basics +
      5. +
    5. + + Creating a Content Provider +
      6. +
    6. + Calendar Provider +
    -

    See also

    -
      -
    1. Calendar Provider
      2. -
    + +

    Related Samples

    +
      +
    1. + + Contact Manager application +
      2. +
    2. + + "Cursor (People)" + +
      3. +
    3. + + "Cursor (Phones)" +
      4. +
    - -

    -Content providers store and retrieve data and make it accessible to all -applications. They're the only way to share data across applications; there's -no common storage area that all Android packages can access. -

    - -

    -Android ships with a number of content providers for common data types -(audio, video, images, personal contact information, and so on). You can -see some of them listed in the {@link android.provider android.provider} -package. You can query these providers for the data they contain (although, -for some, you must acquire the proper permission to read the data). -

    - -

    Note: Android 4.0 introduces the Calendar -Provider. For more information, see Calendar -Provider.

    -

    -If you want to make your own data public, you have two options: You can -create your own content provider (a {@link android.content.ContentProvider} -subclass) or you can add the data to an existing provider — if there's -one that controls the same type of data and you have permission to write to it. -

    - -

    -This document is an introduction to using content providers. After a -brief discussion of the fundamentals, it explores how to query a content -provider, how to modify data controlled by a provider, and how to create -a content provider of your own. -

    - - -

    Content Provider Basics

    - -

    -How a content provider actually stores its data under the covers is -up to its designer. But all content providers implement a common interface -for querying the provider and returning results — as well as for -adding, altering, and deleting data. -

    - -

    -It's an interface that clients use indirectly, most generally through -{@link android.content.ContentResolver} objects. You get a ContentResolver -by calling {@link android.content.Context#getContentResolver -getContentResolver()} from within the implementation of an Activity -or other application component: -

    - -
    ContentResolver cr = getContentResolver();
    - -

    -You can then use the ContentResolver's methods to interact with whatever -content providers you're interested in. -

    - -

    -When a query is initiated, the Android system identifies the content provider -that's the target of the query and makes sure that it is up and running. -The system instantiates all ContentProvider objects; you never need to do it -on your own. In fact, you never deal directly with ContentProvider objects -at all. Typically, there's just a single instance of each type of -ContentProvider. But it can communicate with multiple ContentResolver objects -in different applications and processes. The interaction between processes is -handled by the ContentResolver and ContentProvider classes. -

    - - -

    The data model

    - -

    -Content providers expose their data as a simple table on a database model, -where each row is a record and each column is data of a particular type -and meaning. For example, information about people and their phone numbers -might be exposed as follows: -

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    _IDNUMBERNUMBER_KEYLABELNAMETYPE
    13(425) 555 6677425 555 6677Kirkland officeBully Pulpit{@code TYPE_WORK}
    44(212) 555-1234212 555 1234NY apartmentAlan Vain{@code TYPE_HOME}
    45(212) 555-6657212 555 6657Downtown officeAlan Vain{@code TYPE_MOBILE}
    53201.555.4433201 555 4433Love NestRex Cars{@code TYPE_HOME}
    - -

    -Every record includes a numeric {@code _ID} field that uniquely identifies -the record within the table. IDs can be used to match records in related -tables — for example, to find a person's phone number in one table -and pictures of that person in another. -

    - -

    -A query returns a {@link android.database.Cursor} object that can move from -record to record and column to column to read the contents of each field. -It has specialized methods for reading each type of data. So, to read a field, -you must know what type of data the field contains. (There's more on query -results and Cursor objects later.) -

    - - -

    URIs

    - -

    -Each content provider exposes a public URI (wrapped as a {@link android.net.Uri} -object) that uniquely identifies its data set. A content provider that controls -multiple data sets (multiple tables) exposes a separate URI for each one. All -URIs for providers begin with the string "{@code content://}". The {@code content:} -scheme identifies the data as being controlled by a content provider. -

    - -

    -If you're defining a content provider, it's a good idea to also define a -constant for its URI, to simplify client code and make future updates cleaner. -Android defines {@code CONTENT_URI} constants for all the providers that come -with the platform. For example, the URI for the table that matches -phone numbers to people and the URI for the table that holds pictures of -people (both controlled by the Contacts content provider) are: -

    - -

    -

    {@code android.provider.Contacts.Phones.CONTENT_URI} -
    {@code android.provider.Contacts.Photos.CONTENT_URI} -

    - -

    -The URI constant is used in all interactions with the content provider. -Every {@link android.content.ContentResolver} method takes the URI -as its first argument. It's what identifies which provider the ContentResolver -should talk to and which table of the provider is being targeted. -

    - - -

    Querying a Content Provider

    - -

    -You need three pieces of information to query a content provider: -

    - - - -

    -If you're querying a particular record, you also need the ID for that record. -

    - - -

    Making the query

    - -

    -To query a content provider, you can use either the -{@link android.content.ContentResolver#query ContentResolver.query()} -method or the {@link android.app.Activity#managedQuery -Activity.managedQuery()} method. -Both methods take the same set of arguments, and both return a -Cursor object. However, {@code managedQuery()} -causes the activity to manage the life cycle of the Cursor. A managed Cursor -handles all of the niceties, such as unloading itself when the activity pauses, -and requerying itself when the activity restarts. You can ask an Activity to -begin managing an unmanaged Cursor object for you by calling -{@link android.app.Activity#startManagingCursor -Activity.startManagingCursor()}. -

    - -

    -The first argument to either {@link android.content.ContentResolver#query query()} -or {@link android.app.Activity#managedQuery managedQuery()} is the provider URI -— the {@code CONTENT_URI} constant that identifies a particular -ContentProvider and data set (see URIs earlier). -

    - -

    -To restrict a query to just one record, you can append the {@code _ID} value for -that record to the URI — that is, place a string matching the ID as the -last segment of the path part of the URI. For example, if the ID is 23, -the URI would be: -

    - -

    {@code content://. . . ./23}

    - -

    -There are some helper methods, particularly -{@link android.content.ContentUris#withAppendedId -ContentUris.withAppendedId()} and {@link -android.net.Uri#withAppendedPath Uri.withAppendedPath()}, -that make it easy to append an ID to a URI. Both are static methods that return -a Uri object with the ID added. So, for example, if you were looking for record -23 in the database of people contacts, you might construct a query as follows: -

    - -
    -import android.provider.Contacts.People;
-import android.content.ContentUris;
-import android.net.Uri;
-import android.database.Cursor;
-
-// Use the ContentUris method to produce the base URI for the contact with _ID == 23.
-Uri myPerson = ContentUris.withAppendedId(People.CONTENT_URI, 23);
-
-// Alternatively, use the Uri method to produce the base URI.
-// It takes a string rather than an integer.
-Uri myPerson = Uri.withAppendedPath(People.CONTENT_URI, "23");
-
-// Then query for this specific record:
-Cursor cur = managedQuery(myPerson, null, null, null, null);
-
    - -

    -The other arguments to the {@link android.content.ContentResolver#query query()} -and {@link android.app.Activity#managedQuery managedQuery()} methods delimit -the query in more detail. They are: -

    - - - -

    -Let's look at an example query to retrieve a list of contact names and their -primary phone numbers: -

    - -
    -import android.provider.Contacts.People;
-import android.database.Cursor;
-
-// Form an array specifying which columns to return. 
-String[] projection = new String[] {
-                             People._ID,
-                             People._COUNT,
-                             People.NAME,
-                             People.NUMBER
-                          };
-
-// Get the base URI for the People table in the Contacts content provider.
-Uri contacts =  People.CONTENT_URI;
-
-// Make the query. 
-Cursor managedCursor = managedQuery(contacts,
-                         projection, // Which columns to return 
-                         null,       // Which rows to return (all rows)
-                         null,       // Selection arguments (none)
-                         // Put the results in ascending order by name
-                         People.NAME + " ASC");
-
    - -

    -This query retrieves data from the People table of the Contacts content -provider. It gets the name, primary phone number, and unique record ID for -each contact. It also reports the number of records that are returned as -the {@code _COUNT} field of each record. -

    - -

    -The constants for the names of the columns are defined in various interfaces -— {@code _ID} and {@code _COUNT} in -{@link android.provider.BaseColumns BaseColumns}, {@code NAME} in {@link android.provider.Contacts.PeopleColumns PeopleColumns}, and {@code NUMBER} -in {@link android.provider.Contacts.PhonesColumns PhoneColumns}. The -{@link android.provider.Contacts.People Contacts.People} class implements -each of these interfaces, which is why the code example above could refer -to them using just the class name. -

    - - -

    What a query returns

    - -

    -A query returns a set of zero or more database records. The names of the -columns, their default order, and their data types are specific to each -content provider. -But every provider has an {@code _ID} column, which holds a unique numeric -ID for each record. Every provider can also report the number -of records returned as the {@code _COUNT} column; its value -is the same for all rows. -

    - -

    -Here is an example result set for the query in the previous section: -

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    _ID_COUNTNAMENUMBER
    443Alan Vain212 555 1234
    133Bully Pulpit425 555 6677
    533Rex Cars201 555 4433
    - -

    -The retrieved data is exposed by a {@link android.database.Cursor Cursor} -object that can be used to iterate backward or forward through the result -set. You can use this object only to read the data. To add, modify, or -delete data, you must use a ContentResolver object. -

    - - -

    Reading retrieved data

    - -

    -The Cursor object returned by a query provides access to a recordset of -results. If you have queried for a specific record by ID, this set will -contain only one value. Otherwise, it can contain multiple values. -(If there are no matches, it can also be empty.) You -can read data from specific fields in the record, but you must know the -data type of the field, because the Cursor object has a separate method -for reading each type of data — such as {@link -android.database.Cursor#getString getString()}, {@link -android.database.Cursor#getInt getInt()}, and {@link -android.database.Cursor#getFloat getFloat()}. -(However, for most types, if you call the method for reading strings, -the Cursor object will give you the String representation of the data.) -The Cursor lets you request the column name from the index of the column, -or the index number from the column name. -

    - -

    -The following snippet demonstrates reading names and phone numbers from -the query illustrated earlier: -

    - -
    -import android.provider.Contacts.People;
-
-private void getColumnData(Cursor cur){ 
-    if (cur.moveToFirst()) {
-
-        String name; 
-        String phoneNumber; 
-        int nameColumn = cur.getColumnIndex(People.NAME); 
-        int phoneColumn = cur.getColumnIndex(People.NUMBER);
-        String imagePath; 
-    
-        do {
-            // Get the field values
-            name = cur.getString(nameColumn);
-            phoneNumber = cur.getString(phoneColumn);
-           
-	    // Do something with the values. 
-            ... 
-
-        } while (cur.moveToNext());
-
-    }
-}
-
    - -

    -If a query can return binary data, such as an image or sound, the data -may be directly entered in the table or the table entry for that data may be -a string specifying a {@code content:} URI that you can use to get the data. -In general, smaller amounts of data (say, from 20 to 50K or less) are most often -directly entered in the table and can be read by calling -{@link android.database.Cursor#getBlob Cursor.getBlob()}. -It returns a byte array. -

    - -

    -If the table entry is a {@code content:} URI, you should never try to open -and read the file directly (for one thing, permissions problems can make this -fail). Instead, you should call -{@link android.content.ContentResolver#openInputStream -ContentResolver.openInputStream()} to get an -{@link java.io.InputStream} object that you can use to read the data. -

    - - -

    Modifying Data

    - -

    -Data kept by a content provider can be modified by: -

    - - - -

    -All data modification is accomplished using {@link android.content.ContentResolver} -methods. Some content providers require a more restrictive permission for writing -data than they do for reading it. If you don't have permission to write to a -content provider, the ContentResolver methods will fail. -

    - - -

    Adding records

    - -

    -To add a new record to a content provider, first set up a map of key-value pairs -in a {@link android.content.ContentValues} object, where each key matches -the name of a column in the content provider and the value is the desired -value for the new record in that column. Then call {@link -android.content.ContentResolver#insert ContentResolver.insert()} and pass -it the URI of the provider and the ContentValues map. This method returns -the full URI of the new record — that is, the provider's URI with -the appended ID for the new record. You can then use this URI to query and -get a Cursor over the new record, and to further modify the record. -Here's an example: -

    - -
    -import android.provider.Contacts.People;
-import android.content.ContentResolver;
-import android.content.ContentValues; 
-
-ContentValues values = new ContentValues();
-
-// Add Abraham Lincoln to contacts and make him a favorite.
-values.put(People.NAME, "Abraham Lincoln");
-// 1 = the new contact is added to favorites
-// 0 = the new contact is not added to favorites
-values.put(People.STARRED, 1);
-
-Uri uri = getContentResolver().insert(People.CONTENT_URI, values);
-
    - - -

    Adding new values

    - -

    -Once a record exists, you can add new information to it or modify -existing information. For example, the next step in the example above would -be to add contact information — like a phone number or an IM or e-mail -address — to the new entry. -

    - -

    -The best way to add to a record in the Contacts database is to append -the name of the table where the new data goes to the URI for the -record, then use the amended URI to add the new data values. Each -Contacts table exposes a name for this purpose as a {@code -CONTENT_DIRECTORY} constant. The following code continues the previous -example by adding a phone number and e-mail address for the record -just created: -

    - -
    -Uri phoneUri = null;
-Uri emailUri = null;
-
-// Add a phone number for Abraham Lincoln.  Begin with the URI for
-// the new record just returned by insert(); it ends with the _ID
-// of the new record, so we don't have to add the ID ourselves.
-// Then append the designation for the phone table to this URI,
-// and use the resulting URI to insert the phone number.
-phoneUri = Uri.withAppendedPath(uri, People.Phones.CONTENT_DIRECTORY);
-
-values.clear();
-values.put(People.Phones.TYPE, People.Phones.TYPE_MOBILE);
-values.put(People.Phones.NUMBER, "1233214567");
-getContentResolver().insert(phoneUri, values);
-
-// Now add an email address in the same way.
-emailUri = Uri.withAppendedPath(uri, People.ContactMethods.CONTENT_DIRECTORY);
-
-values.clear();
-// ContactMethods.KIND is used to distinguish different kinds of
-// contact methods, such as email, IM, etc. 
-values.put(People.ContactMethods.KIND, Contacts.KIND_EMAIL);
-values.put(People.ContactMethods.DATA, "test@example.com");
-values.put(People.ContactMethods.TYPE, People.ContactMethods.TYPE_HOME);
-getContentResolver().insert(emailUri, values);   
-
    - -

    -You can place small amounts of binary data into a table by calling -the version of {@link android.content.ContentValues#put -ContentValues.put()} that takes a byte array. -That would work for a small icon-like image or a short audio clip, for example. -However, if you have a large amount of binary data to add, such as a photograph -or a complete song, put a {@code content:} URI for the data in the table and call -{@link android.content.ContentResolver#openOutputStream -ContentResolver.openOutputStream()} -with the file's URI. (That causes the content provider to store the data -in a file and record the file path in a hidden field of the record.) -

    - -

    -In this regard, the {@link android.provider.MediaStore} content -provider, the main provider that dispenses image, audio, and video -data, employs a special convention: The same URI that is used with -{@code query()} or {@code managedQuery()} to get meta-information -about the binary data (such as, the caption of a photograph or the -date it was taken) is used with {@code openInputStream()} -to get the data itself. Similarly, the same URI that is used with -{@code insert()} to put meta-information into a MediaStore record -is used with {@code openOutputStream()} to place the binary data there. -The following code snippet illustrates this convention: -

    - -
    -import android.provider.MediaStore.Images.Media;
-import android.content.ContentValues;
-import java.io.OutputStream;
-
-// Save the name and description of an image in a ContentValues map.  
-ContentValues values = new ContentValues(3);
-values.put(Media.DISPLAY_NAME, "road_trip_1");
-values.put(Media.DESCRIPTION, "Day 1, trip to Los Angeles");
-values.put(Media.MIME_TYPE, "image/jpeg");
-
-// Add a new record without the bitmap, but with the values just set.
-// insert() returns the URI of the new record.
-Uri uri = getContentResolver().insert(Media.EXTERNAL_CONTENT_URI, values);
-
-// Now get a handle to the file for that record, and save the data into it.
-// Here, sourceBitmap is a Bitmap object representing the file to save to the database.
-try {
-    OutputStream outStream = getContentResolver().openOutputStream(uri);
-    sourceBitmap.compress(Bitmap.CompressFormat.JPEG, 50, outStream);
-    outStream.close();
-} catch (Exception e) {
-    Log.e(TAG, "exception while writing image", e);
-}
-
    - - -

    Batch updating records

    - -

    -To batch update a group of records (for example, to change "NY" to "New York" -in all fields), call the {@link -android.content.ContentResolver#update ContentResolver.update()} -method with the columns and values to change. -

    - - -

    Deleting a record

    - -

    -To delete a single record, call {{@link -android.content.ContentResolver#delete ContentResolver.delete()} -with the URI of a specific row. -

    -

    -To delete multiple rows, call {@link -android.content.ContentResolver#delete ContentResolver.delete()} -with the URI of the type of record to delete (for example, {@code android.provider.Contacts.People.CONTENT_URI}) and an SQL {@code WHERE} -clause defining which rows to delete. (Caution: -Be sure to include a valid {@code WHERE} clause if you're deleting a general -type, or you risk deleting more records than you intended!). -

    - - -

    Creating a Content Provider

    - -

    -To create a content provider, you must: -

    - - - -

    -The following sections have notes on the last two of these tasks. -

    - - -

    Extending the ContentProvider class

    - -

    -You define a {@link android.content.ContentProvider} subclass to -expose your data to others using the conventions expected by -ContentResolver and Cursor objects. Principally, this means -implementing six abstract methods declared in the ContentProvider class: -

    - -

    {@code query()} -
    {@code insert()} -
    {@code update()} -
    {@code delete()} -
    {@code getType()} -
    {@code onCreate()}

    - -

    -The {@code query()} method must return a {@link android.database.Cursor} object -that can iterate over the requested data. Cursor itself is an interface, but -Android provides some ready-made Cursor objects that you can use. For example, -{@link android.database.sqlite.SQLiteCursor} can iterate over data stored in -an SQLite database. You get the Cursor object by calling any of the {@link -android.database.sqlite.SQLiteDatabase SQLiteDatabase} class's {@code query()} -methods. There are other Cursor implementations — such as {@link -android.database.MatrixCursor} — for data not stored in a database. -

    - -

    -Because these ContentProvider methods can be called from -various ContentResolver objects in different processes and threads, -they must be implemented in a thread-safe manner. -

    - -

    -As a courtesy, you might also want to call {@link android.content.ContentResolver#notifyChange(android.net.Uri,android.database.ContentObserver) -ContentResolver.notifyChange()} to notify listeners when there are -modifications to the data. -

    - -

    -Beyond defining the subclass itself, there are other steps you should take -to simplify the work of clients and make the class more accessible: -

    - - - -

    -For an example of a private content provider implementation, see the -NodePadProvider class in the Notepad sample application that ships with the SDK. -

    - - -

    Declaring the content provider

    - -

    -To let the Android system know about the content provider you've developed, -declare it with a {@code <provider>} element in the application's -AndroidManifest.xml file. Content providers that are not declared in the -manifest are not visible to the Android system -

    - -

    -The {@code name} attribute is the fully qualified name of the ContentProvider -subclass. The {@code authorities} attribute is the authority part of the -{@code content:} URI that identifies the provider. -For example if the ContentProvider subclass is AutoInfoProvider, the -{@code <provider>} element might look like this: -

    - -
    -<provider android:name="com.example.autos.AutoInfoProvider"
-          android:authorities="com.example.autos.autoinfoprovider" 
-          . . . />
-</provider>
-
    - -

    -Note that the {@code authorities} attribute omits the path part of a -{@code content:} URI. For example, if AutoInfoProvider controlled subtables -for different types of autos or different manufacturers, -

    - -

    {@code content://com.example.autos.autoinfoprovider/honda} -
    {@code content://com.example.autos.autoinfoprovider/gm/compact} -
    {@code content://com.example.autos.autoinfoprovider/gm/suv}

    - -

    -those paths would not be declared in the manifest. The authority is what -identifies the provider, not the path; your provider can interpret the path -part of the URI in any way you choose. -

    - -

    -Other {@code <provider>} attributes can set permissions to read and -write data, provide for an icon and text that can be displayed to users, -enable and disable the provider, and so on. Set the {@code multiprocess} -attribute to "{@code true}" if data does not need to be synchronized between -multiple running versions of the content provider. This permits an instance -of the provider to be created in each client process, eliminating the need -to perform IPC. -

    - - -

    Content URI Summary

    - -

    -Here is a recap of the important parts of a content URI: -

    - -

    -Elements of a content URI -

    - -
      -
    1. Standard prefix indicating that the data is controlled by a -content provider. It's never modified.
      2. - -

    2. The authority part of the URI; it identifies the content provider. -For third-party applications, this should be a fully-qualified class name -(reduced to lowercase) to ensure uniqueness. The authority is declared in -the {@code <provider>} element's {@code authorities} attribute:

      - -
      <provider android:name=".TransportationProvider"
-          android:authorities="com.example.transportationprovider"
-          . . .  >
      3. - -

    3. The path that the content provider uses to determine what kind of data is -being requested. This can be zero or more segments long. If the content provider -exposes only one type of data (only trains, for example), it can be absent. -If the provider exposes several types, including subtypes, it can be several -segments long — for example, "{@code land/bus}", "{@code land/train}", -"{@code sea/ship}", and "{@code sea/submarine}" to give four possibilities.

      4. - -

    4. The ID of the specific record being requested, if any. This is the -{@code _ID} value of the requested record. If the request is not limited to -a single record, this segment and the trailing slash are omitted:

      - -

      {@code content://com.example.transportationprovider/trains}

      -
      5. -
    - - + Content providers manage access to a structured set of data. They encapsulate the + data, and provide mechanisms for defining data security. Content providers are the standard + interface that connects data in one process with code running in another process. +

    +

    + When you want to access data in a content provider, you use the + {@link android.content.ContentResolver} object in your + application's {@link android.content.Context} to communicate with the provider as a client. + The {@link android.content.ContentResolver} object communicates with the provider object, an + instance of a class that implements {@link android.content.ContentProvider}. The provider + object receives data requests from clients, performs the requested action, and + returns the results. +

    +

    + You don't need to develop your own provider if you don't intend to share your data with + other applications. However, you do need your own provider to provide custom search + suggestions in your own application. You also need your own provider if you want to copy and + paste complex data or files from your application to other applications. +

    +

    + Android itself includes content providers that manage data such as audio, video, images, and + personal contact information. You can see some of them listed in the reference + documentation for the + android.provider + package. With some restrictions, these providers are accessible to any Android + application. +

    + The following topics describe content providers in more detail: +

    +
    +
    + + Content Provider Basics +
    +
    + How to access data in a content provider when the data is organized in tables. +
    +
    + + Creating a Content Provider +
    +
    + How to create your own content provider. +
    +
    + + Calendar Provider +
    +
    + How to access the Calendar Provider that is part of the Android platform. +
    +
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