From f2960b8d66d7a20f590716f5e51160e77d0d1b24 Mon Sep 17 00:00:00 2001 From: Raphael Moll Date: Tue, 21 Sep 2010 17:10:35 -0700 Subject: Refresh the layoutlib_create doc. Change-Id: I43e92c33d824ace9edd77d90a1b36a5f69d85e7f --- tools/layoutlib/create/README.txt | 200 +++++++++++++++++++++++++++++++------- 1 file changed, 164 insertions(+), 36 deletions(-) diff --git a/tools/layoutlib/create/README.txt b/tools/layoutlib/create/README.txt index 09b392ba7e72..c59e20d51e97 100644 --- a/tools/layoutlib/create/README.txt +++ b/tools/layoutlib/create/README.txt @@ -4,68 +4,196 @@ - Description - --------------- -makeLayoutLib generates a library used by the Eclipse graphical layout editor +Layoutlib_create generates a JAR library used by the Eclipse graphical layout editor to perform layout. - - Usage - --------- - ./makeLayoutLib path/to/android.jar destination.jar + ./layoutlib_create path/to/android.jar destination.jar + + +- Design Overview - +------------------- + +Layoutlib_create uses the "android.jar" containing all the Java code used by Android +as generated by the Android build, right before the classes are converted to a DEX format. + +The Android JAR can't be used directly in Eclipse: +- it contains references to native code (which we want to avoid in Eclipse), +- some classes need to be overridden, for example all the drawing code that is + replaced by Java 2D calls in Eclipse. +- some of the classes that need to be changed are final and/or we need access + to their private internal state. + +Consequently this tool: +- parses the input JAR, +- modifies some of the classes directly using some bytecode manipulation, +- filters some packages and removes some that we don't want to end in the output JAR, +- injects some new classes, +- and generates a modified JAR file that is suitable for the Android plugin + for Eclipse to perform rendering. + +The ASM library is used to do the bytecode modification using its visitor pattern API. + +The layoutlib_create is *NOT* generic. There is no configuration file. Instead all the +configuration is done in the main() method and the CreateInfo structure is expected to +change with the Android platform as new classes are added, changed or removed. + +The resulting JAR is used by layoutlib_bridge (a.k.a. "the bridge"), also part of the +platform, that provides all the necessary missing implementation for rendering graphics +in Eclipse. - Implementation Notes - ------------------------ -The goal of makeLayoutLib is to list all the classes from the input jar and create a new -jar that only keeps certain classes and create stubs for all their dependencies. +The tool works in two phases: +- first analyze the input jar (AsmAnalyzer class) +- then generate the output jar (AsmGenerator class), + + +- Analyzer +---------- + +The goal of the analyzer is to create a graph of all the classes from the input JAR +with their dependencies and then only keep the ones we want. + +To do that, the analyzer is created with a list of base classes to keep -- everything +that derives from these is kept. Currently the one such class is android.view.View: +since we want to render layouts, anything that is sort of the view needs to be kept. + +The analyzer is also given a list of class names to keep in the output. +This is done using shell-like glob patterns that filter on the fully-qualified +class names, for example "android.*.R**" ("*" does not matches dots whilst "**" does, +and "." and "$" are interpreted as-is). +In practice we almost but not quite request the inclusion of full packages. + +With this information, the analyzer parses the input zip to find all the classes. +All classes deriving from the requested bases classes are kept. +All classes which name matched the glob pattern are kept. +The analysis then finds all the dependencies of the classes that are to be kept +using an ASM visitor on the class, the field types, the method types and annotations types. +Classes that belong to the current JRE are excluded. + +The output of the analyzer is a set of ASM ClassReader instances which are then +fed to the generator. + + +- Generator +----------- -First the input jar is parsed to find all the classes defined. +The generator is constructed from a CreateInfo struct that acts as a config file +and lists: +- the classes to inject in the output JAR -- these classes are directly implemented + in layoutlib_create and will be used to interface with the renderer in Eclipse. +- specific methods to override (see method stubs details below). +- specific methods to remove based on their return type. +- specific classes to rename. -In the Main(), the following list of classes are hardcoded (TODO config file later): -- keep all classes that derive from android.view.View. -- keep all classes in the android.view and android.widget packages (sub-packages excluded). -- keep specific classes such as android.policy.PhoneLayoutInflater. +Each of these are specific strategies we use to be able to modify the Android code +to fit within the Eclipse renderer. These strategies are explained beow. -For each class to keep, their dependencies are examined using BCEL. -A dependency is defined as a class needed to instantiate the given class that should be kept, -directly or indirectly. So a dependency is a class that is used by the input class, that is -defined in the input jar and that is not part of the current JRE. +The core method of the generator is transform(): it takes an input ASM ClassReader +and modifies it to produce a byte array suitable for the final JAR file. -Dependencies are computed recursively. +The first step of the transformation is changing the name of the class in case +we requested the class to be renamed. This uses the RenameClassAdapter to also rename +all inner classes and references in methods and types. Note that other classes are +not transformed and keep referencing the original name. -Once all dependencies are found, the final jar can be created. -There are three kind of classes to write: -- classes that are to be kept as-is. They are just dumped in the new jar unchanged. -- classes that are to be kept yet contain native methods or fields. -- classes that are just dependencies. We don't want to expose their implementation in the final - jar. +The TransformClassAdapter is then used to process the potentially renamed class. +All protected or private classes are market as public. +All classes are made non-final. +Interfaces are left as-is. -The implementation of native methods and all methods of mock classes is replaced by a stub -that throws UnsupportedOperationException. +If a method has a return type that must be erased, the whole method is skipped. +Methods are also changed from protected/private to public. +The code of the methods is then kept as-is, except for native methods which are +replaced by a stub. Methods that are to be overridden are also replaced by a stub. -Incidentally, the access level of native and mock classes needs to be changed in order for -native methods to be later overridden. Methods that are "final private native" must become -non-final, non-native and at most protected. Package-default access is changed to public. -Classes that are final are made non-final. Abstract methods are left untouched. +Finally fields are also visited and changed from protected/private to public. +- Method stubs +-------------- ----- -20080617 Replace Class +As indicated above, all native and overridden methods are replaced by a stub. +We don't have the code to replace with in layoutlib_create. +Instead the StubMethodAdapter replaces the code of the method by a call to +OverrideMethod.invokeX(). When using the final JAR, the bridge can register +listeners from these overridden method calls based on the method signatures. -Some classes are basically wrappers over native objects. -Subclassing doesn't work as most methods are either static or we don't -control object creation. In this scenario the idea is to be able to -replace classes in the final jar. +The listeners are currently pretty basic: we only pass the signature of the +method being called, its caller object and a flag indicating whether the +method was native. We do not currently provide the parameters. The listener +can however specify the return value of the overridden method. -Example: android.graphics.Paint would get renamed to OriginalPaint -in the generated jar. Then in the bridge we'll introduce a replacement -Paint class that derives from OriginalPaint. +An extension being worked on is to actually replace these listeners by +direct calls to a delegate class, complete with parameters. + + +- Strategies +------------ + +We currently have 4 strategies to deal with overriding the rendering code +and make it run in Eclipse. Most of these strategies are implemented hand-in-hand +by the bridge (which runs in Eclipse) and the generator. + + +1- Class Injection + +This is the easiest: we currently inject 4 classes, namely: +- OverrideMethod and its associated MethodListener and MethodAdapter are used + to intercept calls to some specific methods that are stubbed out and change + their return value. +- CreateInfo class, which configured the generator. Not used yet, but could + in theory help us track what the generator changed. + + +2- Overriding methods + +As explained earlier, the creator doesn't have any replacement code for +methods to override. Instead it removes the original code and replaces it +by a call to a specific OveriddeMethod.invokeX(). The bridge then registers +a listener on the method signature and can provide an implementation. + + +3- Renaming classes + +This simply changes the name of a class in its definition, as well as all its +references in internal inner classes and methods. +Calls from other classes are not modified -- they keep referencing the original +class name. This allows the bridge to literally replace an implementation. + +An example will make this easier: android.graphics.Paint is the main drawing +class that we need to replace. To do so, the generator renames Paint to _original_Paint. +Later the bridge provides its own replacement version of Paint which will be used +by the rest of the Android stack. The replacement version of Paint can still use +(either by inheritance or delegation) all the original non-native code of _original_Paint +if it so desires. + +Some of the Android classes are basically wrappers over native objects and since +we don't have the native code in Eclipse, we need to provide a full alternate +implementation. Sub-classing doesn't work as some native methods are static and +we don't control object creation. This won't rename/replace the inner static methods of a given class. +4- Method erasure based on return type + +This is mostly an implementation detail of the bridge: in the Paint class +mentioned above, some inner static classes are used to pass around +attributes (e.g. FontMetrics, or the Style enum) and all the original implementation +is native. + +In this case we have a strategy that tells the generator that anything returning, for +example, the inner class Paint$Style in the Paint class should be discarded and the +bridge will provide its own implementation. + +-- +end -- cgit v1.2.3