Android View源码解读 DecorView与ViewRootImpl浅谈

public void setContentView(@LayoutRes int layoutResID) {
   getWindow().setContentView(layoutResID); //调用getWindow方法，返回mWindow
   initWindowDecorActionBar();
}
...
public Window getWindow() {  
   return mWindow;
}

final void attach(Context context, ActivityThread aThread,
      Instrumentation instr, IBinder token, int ident,
      Application application, Intent intent, ActivityInfo info,
      CharSequence title, Activity parent, String id,
      NonConfigurationInstances lastNonConfigurationInstances,
      Configuration config, String referrer, IVoiceInteractor voiceInteractor) {
    ...
    mWindow = new PhoneWindow(this);
    ...
  }

@Override
public void setContentView(int layoutResID) {
  // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window
  // decor, when theme attributes and the like are crystalized. Do not check the feature
  // before this happens.
  if (mContentParent == null) { // 1
    installDecor();
  } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
    mContentParent.removeAllViews();
  }

  if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
    final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
        getContext());
    transitionTo(newScene);
  } else {
    mLayoutInflater.inflate(layoutResID, mContentParent); // 2
  }
  final Callback cb = getCallback();
  if (cb != null && !isDestroyed()) {
    cb.onContentChanged();
  }
}

// This is the view in which the window contents are placed. It is either
// mDecor itself, or a child of mDecor where the contents go.
private ViewGroup mContentParent;

private void installDecor() {
  if (mDecor == null) {
    mDecor = generateDecor(); // 1
    mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
    mDecor.setIsRootNamespace(true);
    if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
      mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
    }
  }
  if (mContentParent == null) {
    mContentParent = generateLayout(mDecor); // 2
    ...
    } 
  }
}

protected DecorView generateDecor() {
  return new DecorView(getContext(), -1);
}

protected ViewGroup generateLayout(DecorView decor) {
    // Apply data from current theme.
    // 从主题文件中获取样式信息
    TypedArray a = getWindowStyle();

    ...

    if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {
      requestFeature(FEATURE_NO_TITLE);
    } else if (a.getBoolean(R.styleable.Window_windowActionBar, false)) {
      // Don't allow an action bar if there is no title.
      requestFeature(FEATURE_ACTION_BAR);
    }

    if(...){
      ...
    }

    // Inflate the window decor.
    // 加载窗口布局
    int layoutResource;
    int features = getLocalFeatures();
    // System.out.println("Features: 0x" + Integer.toHexString(features));
    if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
      layoutResource = R.layout.screen_swipe_dismiss;
    } else if(...){
      ...
    }

    View in = mLayoutInflater.inflate(layoutResource, null);  //加载layoutResource
    decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT)); //往DecorView中添加子View，即mContentParent
    mContentRoot = (ViewGroup) in;

    ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT); // 这里获取的就是mContentParent
    if (contentParent == null) {
      throw new RuntimeException("Window couldn't find content container view");
    }

    if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) {
      ProgressBar progress = getCircularProgressBar(false);
      if (progress != null) {
        progress.setIndeterminate(true);
      }
    }

    if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
      registerSwipeCallbacks();
    }

    // Remaining setup -- of background and title -- that only applies
    // to top-level windows.
    ...

    return contentParent;
  }

final void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward) { 
  //...
  ActivityClientRecord r = performResumeActivity(token, clearHide); // 这里会调用到onResume()方法

  if (r != null) {
    final Activity a = r.activity;

    //...
    if (r.window == null && !a.mFinished && willBeVisible) {
      r.window = r.activity.getWindow(); // 获得window对象
      View decor = r.window.getDecorView(); // 获得DecorView对象
      decor.setVisibility(View.INVISIBLE);
      ViewManager wm = a.getWindowManager(); // 获得windowManager对象
      WindowManager.LayoutParams l = r.window.getAttributes();
      a.mDecor = decor;
      l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
      l.softInputMode |= forwardBit;
      if (a.mVisibleFromClient) {
        a.mWindowAdded = true;
        wm.addView(decor, l); // 调用addView方法
      }
      //...
    }
  }
}

public final class WindowManagerImpl implements WindowManager {  
  private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();
  ...
  @Override
  public void addView(View view, ViewGroup.LayoutParams params) {
    mGlobal.addView(view, params, mDisplay, mParentWindow);
  }
}

public void addView(View view, ViewGroup.LayoutParams params,
      Display display, Window parentWindow) {
    ...

    ViewRootImpl root;
    View panelParentView = null;

    synchronized (mLock) {
      ...

      root = new ViewRootImpl(view.getContext(), display); // 1

      view.setLayoutParams(wparams);

      mViews.add(view);
      mRoots.add(root);
      mParams.add(wparams);
    }

    // do this last because it fires off messages to start doing things
    try {
      root.setView(view, wparams, panelParentView); // 2
    } catch (RuntimeException e) {
      // BadTokenException or InvalidDisplayException, clean up.
      synchronized (mLock) {
        final int index = findViewLocked(view, false);
        if (index >= 0) {
          removeViewLocked(index, true);
        }
      }
      throw e;
    }
  }