[Android 学习笔记] instant-run 源码学习 ( 3 )

handleHotSwapPatch 方法的具体实现:

  private int handleHotSwapPatch(int updateMode, ApplicationPatch patch)
  {
    if (Log.isLoggable("InstantRun", 2)) {
      Log.v("InstantRun", "Received incremental code patch");
    }
    try
    {
      String dexFile = FileManager.writeTempDexFile(patch.getBytes());
      if (dexFile == null)
      {
        Log.e("InstantRun", "No file to write the code to");
        return updateMode;
      }
      if (Log.isLoggable("InstantRun", 2)) {
        Log.v("InstantRun", "Reading live code from " + dexFile);
      }
      String nativeLibraryPath = FileManager.getNativeLibraryFolder().getPath();
      
      DexClassLoader dexClassLoader = new DexClassLoader(dexFile, this.context.getCacheDir().getPath(), nativeLibraryPath, getClass().getClassLoader());
      
      Class aClass = Class.forName("com.android.tools.fd.runtime.AppPatchesLoaderImpl", true, dexClassLoader);
      try
      {
        if (Log.isLoggable("InstantRun", 2)) {
          Log.v("InstantRun", "Got the patcher class " + aClass);
        }
        PatchesLoader loader = (PatchesLoader)aClass.newInstance();
        if (Log.isLoggable("InstantRun", 2)) {
          Log.v("InstantRun", "Got the patcher instance " + loader);
        }
        String[] getPatchedClasses = (String[])aClass.getDeclaredMethod("getPatchedClasses", new Class[0]).invoke(loader, new Object[0]);
        if (Log.isLoggable("InstantRun", 2))
        {
          Log.v("InstantRun", "Got the list of classes ");
          for (String getPatchedClass : getPatchedClasses) {
            Log.v("InstantRun", "class " + getPatchedClass);
          }
        }
        if (!loader.load()) {
          updateMode = 3;
        }
      }
      catch (Exception e)
      {
        Log.e("InstantRun", "Couldn't apply code changes", e);
        e.printStackTrace();
        updateMode = 3;
      }
    }
    catch (Throwable e)
    {
      Log.e("InstantRun", "Couldn't apply code changes", e);
      updateMode = 3;
    }
    return updateMode;
  }

首先将 patch 数据保存到文件, 根据 patch
保存路径创建一个DexClassLoader 对象, 这样就可以通过该 DexClassLoader 对象获取 patch 中的类信息并实例化相应对象, 首先实例化 patch 中的 AppPatchesLoaderImpl 对象, 前面笔记中可以看到 AppPatchesLoaderImpl 是继承 AbstractPatchesLoaderImpl, AppPatchesLoaderImpl 只是复写了 getPatchedClasses 方法, 在 Demo 项目中返回 "org.demo.example.MainActivity$1", 然后调用 AppPatchesLoaderImpl 的 load 方法, 具体实现是在父类 AbstractPatchesLoaderImpl 中:

  public boolean load()
  {
    try
    {
      for (String className : getPatchedClasses())
      {
        ClassLoader cl = getClass().getClassLoader();
        Class aClass = cl.loadClass(className + "$override");
        Object o = aClass.newInstance();
        Class originalClass = cl.loadClass(className);
        Field changeField = originalClass.getDeclaredField("$change");
        
        changeField.setAccessible(true);
        
        Object previous = changeField.get(null);
        if (previous != null)
        {
          Field isObsolete = previous.getClass().getDeclaredField("$obsolete");
          if (isObsolete != null) {
            isObsolete.set(null, Boolean.valueOf(true));
          }
        }
        changeField.set(null, o);
        if ((Log.logging != null) && (Log.logging.isLoggable(Level.FINE))) {
          Log.logging.log(Level.FINE, String.format("patched %s", new Object[] { className }));
        }
      }
    }
    catch (Exception e)
    {
      if (Log.logging != null) {
        Log.logging.log(Level.SEVERE, String.format("Exception while patching %s", new Object[] { "foo.bar" }), e);
      }
      return false;
    }
    return true;
  }

首先创建具体补丁 MainActivity$override 对象, 并将该对象复制给 MainActivity 类的 $change 变量, 到此根据之前的分析, 在 MainActivity 对象中调用方法都会走到 MainActivity$override 对象的对应方法, 修改代码后不需要重新安装 APP 就能生效.

替换资源文件

上面说的都是源码补丁, 如果修改了图片或布局, 就通过创建 一个新的AssetManager 对象, 并调用其 addAssetPath 方法加载变更的资源数据, 并替换已经创建的 Activity 对象中的 resource.mAssets 变量为新的 AssetManager 对象, 然后重启 Activity 就可以生效了, 具体实现源码在 MonkeyPatcher 类中, 有兴趣的童鞋可以了解一下