Android中Window添加View的底层原理

2019-12-10 18:54:25刘景俊

由上可知如果是removeViewImmediate,立即调用doDie,如果是removeView,用handler发送消息,ViewRootImpl中的Handler会处理消息并调用doDie。重点看下doDie:

void doDie() { 
    checkThread(); 
    if (LOCAL_LOGV) Log.v(TAG, "DIE in " + this + " of " + mSurface); 
    synchronized (this) { 
      if (mRemoved) { 
        return; 
      } 
      mRemoved = true; 
      if (mAdded) { 
        dispatchDetachedFromWindow(); 
      } 
 
      if (mAdded && !mFirst) { 
        destroyHardwareRenderer(); 
 
        if (mView != null) { 
          int viewVisibility = mView.getVisibility(); 
          boolean viewVisibilityChanged = mViewVisibility != viewVisibility; 
          if (mWindowAttributesChanged || viewVisibilityChanged) { 
            // If layout params have been changed, first give them 
            // to the window manager to make sure it has the correct 
            // animation info. 
            try { 
              if ((relayoutWindow(mWindowAttributes, viewVisibility, false) 
                  & WindowManagerGlobal.RELAYOUT_RES_FIRST_TIME) != 0) { 
                mWindowSession.finishDrawing(mWindow); 
              } 
            } catch (RemoteException e) { 
            } 
          } 
 
          mSurface.release(); 
        } 
      } 
 
      mAdded = false; 
    } 
    WindowManagerGlobal.getInstance().doRemoveView(this); 
  } 

主要做四件事:
1.垃圾回收相关工作,比如清数据,回调等。
2.通过Session的remove方法删除Window,最终调用WindowManagerService的removeWindow

3.调用dispathDetachedFromWindow,在内部会调用onDetachedFromWindow()和onDetachedFromWindowInternal()。当view移除时会调用onDetachedFromWindow,它用于作一些资源回收。
4.通过doRemoveView刷新数据,删除相关数据,如在mRoot,mDyingViews中删除对象等。

void doRemoveView(ViewRootImpl root) { 
    synchronized (mLock) { 
      final int index = mRoots.indexOf(root); 
      if (index >= 0) { 
        mRoots.remove(index); 
        mParams.remove(index); 
        final View view = mViews.remove(index); 
        mDyingViews.remove(view); 
      } 
    } 
    if (HardwareRenderer.sTrimForeground && HardwareRenderer.isAvailable()) { 
      doTrimForeground(); 
    } 
  }