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      1 # View Compiler
      2 
      3 This directory contains an experimental compiler for layout files.
      4 
      5 It will take a layout XML file and produce a CompiledLayout.java file with a
      6 specialized layout inflation function.
      7 
      8 To use it, let's assume you had a layout in `my_layout.xml` and your app was in
      9 the Java language package `com.example.myapp`. Run the following command:
     10 
     11     viewcompiler my_layout.xml --package com.example.myapp --out CompiledView.java
     12 
     13 This will produce a `CompiledView.java`, which can then be compiled into your
     14 Android app. Then to use it, in places where you would have inflated
     15 `R.layouts.my_layout`, instead call `CompiledView.inflate`.
     16 
     17 Precompiling views like this generally improves the time needed to inflate them.
     18 
     19 This tool is still in its early stages and has a number of limitations.
     20 * Currently only one layout can be compiled at a time.
     21 * `merge` and `include` nodes are not supported.
     22 * View compilation is a manual process that requires code changes in the
     23   application.
     24 * This only works for apps that do not use a custom layout inflater.
     25 * Other limitations yet to be discovered.
     26 
     27 ## DexBuilder Tests
     28 
     29 The DexBuilder has several low-level end to end tests to verify generated DEX
     30 code validates, runs, and has the correct behavior. There are, unfortunately, a
     31 number of pieces that must be added to generate new tests. Here are the
     32 components:
     33 
     34 * `dex_testcase_generator` - Written in C++ using `DexBuilder`. This runs as a
     35   build step produce the DEX files that will be tested on device. See the
     36   `genrule` named `generate_dex_testcases` in `Android.bp`. These files are then
     37   copied over to the device by TradeFed when running tests.
     38 * `DexBuilderTest` - This is a Java Language test harness that loads the
     39   generated DEX files and exercises methods in the file.
     40 
     41 To add a new DEX file test, follow these steps:
     42 1. Modify `dex_testcase_generator` to produce the DEX file.
     43 2. Add the filename to the `out` list of the `generate_dex_testcases` rule in
     44    `Android.bp`.
     45 3. Add a new `push` option to `AndroidTest.xml` to copy the DEX file to the
     46    device.
     47 4. Modify `DexBuilderTest.java` to load and exercise the new test.
     48 
     49 In each case, you should be able to cargo-cult the existing test cases.
     50 
     51 In general, you can probably get by without adding a new generated DEX file, and
     52 instead add more methods to the files that are already generated. In this case,
     53 you can skip all of steps 2 and 3 above, and simplify steps 1 and 4.
     54