顶层视图DecorView添加到窗口的过程

电玩女神 2023-10-17 10:41 9阅读 0赞

## 顶层视图DecorView添加到窗口的过程 ##

![这里写图片描述][SouthEast]

在ActivityThread中，当Activity被创建完毕后，会将DecorView添加到Window中。

ActivityThread\#handleResumeActivity()

final void handleResumeActivity(IBinder token,
            boolean clearHide, boolean isForward, boolean reallyResume) {   
        //...
         r.window = r.activity.getWindow();
        View decor = r.window.getDecorView();
        //先将DecorView设为不可见
        decor.setVisibility(View.INVISIBLE);
        ViewManager wm = a.getWindowManager();
        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;
            //将DecorView添加到Window中
            wm.addView(decor, l);
        }
    }

再来看windowManager的实现类WindowManagerImpl\#addView()

@Override
    public void addView(View view, ViewGroup.LayoutParams params) {
        mGlobal.addView(view, params, mDisplay, mParentWindow);
    }

可以看到，其调用了WindowManagerGlobal\#addView()

public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
        //...
        final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)param;
        //...
    
        ViewRootImpl root;
        View panelParentView = null;
    
        synchronized (mLock) {
            //...
    
            root = new ViewRootImpl(view.getContext(), display);
    
            view.setLayoutParams(wparams);
    
            mViews.add(view);
            mRoots.add(root);
            mParams.add(wparams);
        }
    
        //view(DecorView)和root建立关联
        root.setView(view, wparams, panelParentView);   
    }

在此处，DecorView和Root建立了关联 ViewRootImplw\#setView()

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
        //...
        requestLayout();
        //...   
    }

再来看ViewRootImplw\#requestLayout()

@Override
    public void requestLayout() {
        if (!mHandlingLayoutInLayoutRequest) {
            checkThread();
            mLayoutRequested = true;
            scheduleTraversals();
        }
    }

调用了scheduleTraversals()

void scheduleTraversals() {
        if (!mTraversalScheduled) {
           //...
           mChoreographer.postCallback(
                   Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
           //...
        }
    }

mTraversalRunnable是什么呢？ 是一个Runnable对象，内部调用了doTraversal()

final class TraversalRunnable implements Runnable {
        @Override
        public void run() {
            doTraversal();
        }
    }

再来看doTraversal()

void doTraversal() {
        //...
        performTraversals();
        //...
    }

从performTraversals()开始，进入View的绘制流程，完成VIew的measure、layout、draw三大过程。

[SouthEast]: https://img-blog.csdn.net/20170218121612348?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvRXRoYW5Dbw==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast