Android ViewRootImpl源码分析

文章目录

[Android ViewRootImpl源码分析](#Android ViewRootImpl源码分析)

Android ViewRootImpl源码分析

概述

ViewRootImpl 是连接 View 层和 WindowManagerServcie(WMS) 的桥梁。

作用：

负责管理整个 View 树的布局、测量、绘制流程
负责与 WMS 通信，完成窗口的添加、更新、移除
调度 InputEventReceiver，处理输入事件、焦点变化等。

流程

ActivityThread.handleLaunchActivity():

Instrumentation.newActivity()
Instrumentation.callActivityOnCreate()
Activity.performCreate()
Activity.onCreate()
Activity.setContentView()

ActivityThread.handleResumeActivity():

ActivityThread.performResumeActivity():
1. Activity.performResume()
2. Instrumentation.callActivityOnResume()
3. Activity.onResume()
Activity.makeVisible():
1. WindowManagerImpl.addView()
2. WindowManagerGlobal.addView()：创建ViewRootImpl实例，并关联ViewRootImpl和DecorView
3. ViewRootImpl.setView()
4. ViewRootImpl.requestLayout()
5. ViewRootImpl.scheduleTraversals()
6. ViewRootImpl.doTraversal()
7. ViewRootImpl.performTraversals()
8. ViewRootImpl.performMeasure()：测量流程
9. ViewRootImpl.performLayout()：布局流程
10. ViewRootImpl.performDraw()：绘制流程

源码分析

ActivityThread.handleResumeActivity()

java 复制代码

public void handleResumeActivity(ActivityClientRecord r, boolean finalStateRequest,
        boolean isForward, boolean shouldSendCompatFakeFocus, String reason) {
    // Activity的状态由可见转变为可见可交互
    // 依次调用：ActivityThread.performResumeActivity() → Activity.performResume() → Instrumentation.callActivityOnResume() → Activity.onResume()
    if (!performResumeActivity(r, finalStateRequest, reason)) {
        return;
    }
    
    // 调用Activity.makeVisible()
    r.activity.makeVisible();
}

Activity.makeVisible()

java 复制代码

void makeVisible() {
    if (!mWindowAdded) {
        ViewManager wm = getWindowManager();
        // 代理转发，实际由WindowManagerImpl处理，并传入DecorView
        wm.addView(mDecor, getWindow().getAttributes());
        mWindowAdded = true;
    }
    mDecor.setVisibility(View.VISIBLE);
}

WindowManagerImpl.addView()

java 复制代码

@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
    applyTokens(params);
    // 调用WindowManagerGlobal.addView()
    mGlobal.addView(view, params, mContext.getDisplayNoVerify(), mParentWindow,
            mContext.getUserId());
}

WindowManagerGlobal.addView()

java 复制代码

public void addView(View view, ViewGroup.LayoutParams params,
                    Display display, Window parentWindow, int userId) {     
    final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
    ViewRootImpl root;
    View panelParentView = null;

    synchronized (mLock) {

        // 创建ViewRootImple实例
        if (windowlessSession == null) {
            root = new ViewRootImpl(view.getContext(), display);
        } else {
            root = new ViewRootImpl(view.getContext(), display,
                                    windowlessSession, new WindowlessWindowLayout());
        }

        // DecorView设置布局参数
        view.setLayoutParams(wparams);

        // ViewRootImple关联DecorView
        root.setView(view, wparams, panelParentView, userId);
    }
}

ViewRootImpl.setView()

java 复制代码

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView,
        int userId) {
    synchronized (this) {
        if (mView == null) {
            // 保存DecorView
            mView = view;

            // 请求布局
            requestLayout();
             
            // 通过IBinder向WMS申请窗口和画布
            res = mWindowSession.addToDisplayAsUser(mWindow, mWindowAttributes,
                        getHostVisibility(), mDisplay.getDisplayId(), userId,
                        mInsetsController.getRequestedVisibleTypes(), inputChannel, mTempInsets,
                        mTempControls, attachedFrame, compatScale);
            
            // 绑定父子关系，将DecorView的父容器设置为ViewRootImpl
            view.assignParent(this);
    }
}

ViewRootImpl.requestLayout()

java 复制代码

@Override
public void requestLayout() {
    if (!mHandlingLayoutInLayoutRequest) {
        checkThread();
        mLayoutRequested = true;
        // 调度遍历流程
        scheduleTraversals();
    }
}

ViewRootImpl.scheduleTraversals()

java 复制代码

void scheduleTraversals() {
    if (!mTraversalScheduled) {
        mTraversalScheduled = true;
        mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
        // 插入同步屏障， 最终调用doTraversal()
        mChoreographer.postCallback(
            Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
        notifyRendererOfFramePending();
        pokeDrawLockIfNeeded();
    }
}

final TraversalRunnable mTraversalRunnable = new TraversalRunnable();

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

ViewRootImpl.doTraversal()

java 复制代码

void doTraversal() {
    if (mTraversalScheduled) {
        mTraversalScheduled = false;
        mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);

        if (mProfile) {
            Debug.startMethodTracing("ViewAncestor");
        }
	
        // 绘制流程
        performTraversals(); 
    }
}

ViewRootImpl.performTraversals()

java 复制代码

private void performTraversals() {
    // 测量阶段
    performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
    
    // 布局阶段
    performLayout(lp, mWidth, mHeight);   

    // 绘制阶段
    performDraw(mActiveSurfaceSyncGroup)
}