am 733217e6: Merge "Update layoutlib create README"
* commit '733217e6768757c50e1ac38644c2ecdbe522e8f5':
Update layoutlib create README
diff --git a/tools/layoutlib/create/README.txt b/tools/layoutlib/create/README.txt
index ef2b185..6e0a300 100644
--- a/tools/layoutlib/create/README.txt
+++ b/tools/layoutlib/create/README.txt
@@ -4,46 +4,45 @@
- Description -
---------------
-Layoutlib_create generates a JAR library used by the Eclipse graphical layout editor
-to perform layout.
+Layoutlib_create generates a JAR library used by the Eclipse graphical layout editor to perform
+layout.
- Usage -
---------
- ./layoutlib_create path/to/android.jar destination.jar
+ ./layoutlib_create destination.jar path/to/android1.jar path/to/android2.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.
+Layoutlib_create uses a few jars from the framework containing 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.
+These jars can't be used directly in Eclipse as:
+- they 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 those we don't want in the output JAR,
- injects some new classes,
-- generates a modified JAR file that is suitable for the Android plugin
- for Eclipse to perform rendering.
+- 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 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.
+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.
@@ -58,97 +57,96 @@
- 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.
+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 a view needs to be kept.
+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 a 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 "$" are interpreted as-is).
-In practice we almost but not quite request the inclusion of full packages.
+The analyzer is also given a list of class names to keep in the output. This is done using
+shell-like glob patterns that filter on the fully-qualified class names, for example "android.*.R**"
+("*" does not matches dots whilst "**" does, and "." and "$" are interpreted as-is). In practice we
+almost but not quite request the inclusion of full packages.
-The analyzer is also given a list of classes to exclude. A fake implementation of these
-classes is injected by the Generator.
+The analyzer is also given a list of classes to exclude. A fake implementation of these classes is
+injected by the Generator.
-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.
+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 whose name match 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.
+The output of the analyzer is a set of ASM ClassReader instances which are then fed to the
+generator.
- Generator
-----------
-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.
+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 for which to delegate calls.
- specific methods to remove based on their return type.
- specific classes to rename.
- specific classes to refactor.
-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.
+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.
-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.
+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.
The first step of the transformation is to implement the method delegates.
-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 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.
-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.
+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.
Finally fields are also visited and changed from protected/private to public.
-The next 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.
+The next 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.
-The class is then fed to RefactorClassAdapter which is like RenameClassAdapter but
-updates the references in all classes. This is used to update the references of classes
-in the java package that were added in the Dalvik VM but are not a part of the standard
-JVM. The existing classes are modified to update all references to these non-standard
-classes. An alternate implementation of these (com.android.tools.layoutlib.java.*) is
-injected.
+The class is then fed to RefactorClassAdapter which is like RenameClassAdapter but updates the
+references in all classes. This is used to update the references of classes in the java package that
+were added in the Dalvik VM but are not a part of the standard JVM. The existing classes are
+modified to update all references to these non-standard classes. An alternate implementation of
+these (com.android.tools.layoutlib.java.*) is injected.
-The ClassAdapters are chained together to achieve the desired output. (Look at section
-2.2.7 Transformation chains in the asm user guide, link in the References.) The order of
-execution of these is:
+RenameClassAdapter and RefactorClassAdapter both inherit from AbstractClassAdapter which changes the
+class version (version of the JDK used to compile the class) to 50 (corresponding to Java 6), if the
+class was originally compiled with Java 7 (version 51). This is because we don't currently generate
+the StackMapTable correctly and Java 7 VM enforces that classes with version greater than 51 have
+valid StackMapTable. As a side benefit of this, we can continue to support Java 6 because Java 7 on
+Mac has horrible font rendering support.
+
+The ClassAdapters are chained together to achieve the desired output. (Look at section 2.2.7
+Transformation chains in the asm user guide, link in the References.) The order of execution of
+these is:
ClassReader -> [DelegateClassAdapter] -> TransformClassAdapter -> [RenameClassAdapter] ->
RefactorClassAdapter -> ClassWriter
- Method stubs
--------------
-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
+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.
-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.
+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.
This strategy is now obsolete and replaced by the method delegates.
@@ -156,97 +154,89 @@
- Strategies
------------
-We currently have 6 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.
+We currently have 6 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 the following classes:
-- 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.
-- AutoCloseable and Objects are part of Java 7. To enable us to still run on Java 6, new
- classes are injected. The implementation for these classes has been taken from
- Android's libcore (platform/libcore/luni/src/main/java/java/...).
-- Charsets, IntegralToString and UnsafeByteSequence are not part of the standard JAVA VM.
- They are added to the Dalvik VM for performance reasons. An implementation that is very
- close to the original (which is at platform/libcore/luni/src/main/java/...) is injected.
- Since these classees were in part of the java package, where we can't inject classes,
- all references to these have been updated (See strategy 4- Refactoring Classes).
+- 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.
+- AutoCloseable and Objects are part of Java 7. To enable us to still run on Java 6, new classes are
+ injected. The implementation for these classes has been taken from Android's libcore
+ (platform/libcore/luni/src/main/java/java/...).
+- Charsets, IntegralToString and UnsafeByteSequence are not part of the standard JAVA VM. They are
+ added to the Dalvik VM for performance reasons. An implementation that is very close to the
+ original (which is at platform/libcore/luni/src/main/java/...) is injected. Since these classees
+ were in part of the java package, where we can't inject classes, all references to these have been
+ updated (See strategy 4- Refactoring Classes).
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.
+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.
-This strategy is now obsolete and replaced by the method delegates.
-See strategy 5 below.
+This strategy is now obsolete and replaced by the method delegates (See strategy 6- Method
+Delegates).
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.
+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.
+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.
+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- Refactoring classes
-This is very similar to the Renaming classes except that it also updates the reference in
-all classes. This is done for classes which are added to the Dalvik VM for performance
-reasons but are not present in the Standard Java VM. An implementation for these classes
-is also injected.
+This is very similar to the Renaming classes except that it also updates the reference in all
+classes. This is done for classes which are added to the Dalvik VM for performance reasons but are
+not present in the Standard Java VM. An implementation for these classes is also injected.
5- 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.
+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$Style in the Paint class should be discarded and the
-bridge will provide its own implementation.
+In this case we have a strategy that tells the generator that anything returning, for example, the
+inner class Paint$Style in the Paint class should be discarded and the bridge will provide its own
+implementation.
6- Method Delegates
-This strategy is used to override method implementations.
-Given a method SomeClass.MethodName(), 1 or 2 methods are generated:
-a- A copy of the original method named SomeClass.MethodName_Original().
- The content is the original method as-is from the reader.
- This step is omitted if the method is native, since it has no Java implementation.
-b- A brand new implementation of SomeClass.MethodName() which calls to a
- non-existing static method named SomeClass_Delegate.MethodName().
- The implementation of this 'delegate' method is done in layoutlib_brigde.
+This strategy is used to override method implementations. Given a method SomeClass.MethodName(), 1
+or 2 methods are generated:
+a- A copy of the original method named SomeClass.MethodName_Original(). The content is the original
+method as-is from the reader. This step is omitted if the method is native, since it has no Java
+implementation.
+b- A brand new implementation of SomeClass.MethodName() which calls to a non-existing static method
+named SomeClass_Delegate.MethodName(). The implementation of this 'delegate' method is done in
+layoutlib_brigde.
-The delegate method is a static method.
-If the original method is non-static, the delegate method receives the original 'this'
-as its first argument. If the original method is an inner non-static method, it also
-receives the inner 'this' as the second argument.
+The delegate method is a static method. If the original method is non-static, the delegate method
+receives the original 'this' as its first argument. If the original method is an inner non-static
+method, it also receives the inner 'this' as the second argument.