add Activity 显示原理

blogs/Android/Framework/Interview/Activity 组件相关/Activity 的显示原理.md

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+---
+Activity 的显示原理
+---
+
+1. Activity 的显示原理（Window/DecorView/ViewRoot）
+2. Activity 的 UI 刷新机制（Vsync/Choreographer）
+3. UI 的绘制原理（Measure/Layout/Draw）
+4. Surface 原理（Surface/SurfaceFlinger）
+
+#### 显示原理
+
+1. setContentView 原理是什么？
+2. Activity 在 onResume 之后才会显示的原因是什么？
+3. ViewRoot 是干嘛的，是 View Tree 的 rootView 么？
+
+```java
+public void setContentView(int layoutResID) {
+	getWindow().setContentView(layoutResID);
+	//...
+}
+```
+
+```java
+final void attach(Context context, ){
+	mWindow = new PhoneWindow(this);
+}
+```
+
+```java
+// PhoneWindow#setContentView
+public void setContentView(int layoutResID) {
+    if(mContentParent == null) {
+        installDecor();
+    }
+    mLayoutInflater.inflate(layoutResID, mContentParent);
+}
+
+private void installDecor() {
+    // FrameLayout
+    mDecor = new DecorView(getContext());
+    // 根据 Window Feature 选择一个系统布局
+    View in = mLayoutInflater.inflate(layoutResource, null);
+    mDecor.addView(in, ...);
+    mContentParent = findViewById(ID_ANDROID_CONTENT);
+}
+```
+
+```java
+final void handleResumeActivity(IBinder token) {
+	ActivityClientRecord r = performResumeActivity(token, );
+    final Activity a = r.activity;
+    
+    if(r.window == null && !a.mFinished) {
+        r.window = r.activity.getWindow();
+        View decor = r.window.getDecorView();
+        
+        ViewManager wm = a.getWindowManager();
+        a.mDecor = decor;
+        wm.addview(decor, l);
+    }
+    r.activity.makeVisible();
+}
+```
+
+```java
+// ViewManager#addView
+void addView(View view, ViewGroup.LayoutParams params, ){
+	ViewRootImpl root = new ViewRootImpl(view.getContext(), );
+    root.setView(view, wparams, panelParentView);
+}
+```
+
+```java
+// ViewRootImpl#setView
+public void setView(View view, ) {
+    if(mView == null) {
+        mView = view;
+        requestLayout();
+        //...
+        mWindowSession.addToDisplay(mWindow, ...);
+    }
+}
+```
+
+```java
+public void requestLayout() {
+	scheduleTraversals();
+}
+void scheduleTraversals() {
+    mChoreographer.postCallback(..., mTraversalRunnable, null);
+}
+class TraversalRunnable implements Runnable {
+    public void run() {
+        doTraversal();
+    }
+}
+void doTraversal() {
+    performTraversals();
+}
+private void performTraversals() {
+    //...
+    relayoutWindow(params, ...);
+    performMeasure(childWidthMeasureSpec, ...);
+    performLayout(lp, desiredWindowWidth, ...);
+    performDraw();
+}
+// 向 WMS 申请 Surface
+int relayoutWindow(WindowManager.LayoutParams params, ...) {
+    mWindowSession.relayout(..., mSurface);
+}
+```
+
+```java
+// static class W extends IWindow.Stub {...}
+mWindowSession.addToDisplay(mWindow, ...);
+public int addToDisplay(IWindow window, int seq, ...) {
+    // WMS 统一管理 Window，分配 Surface
+    return mService.addWindow(this, window, seq, attrs, ...);
+}
+
+IWindowManager windowManager = getWindowManagerService();
+sWindowSession = windowManager.openSession(...);
+
+IWindowSession openSession(IWindowSessionCallback callback, ...) {
+    Session session = new Session(this, callback, client, inputContext);
+    return session;
+}
+```
+
+WMS 的主要作用：
+
+1. 分配 Surface
+2. 掌管 Surface 显示顺序以及位置尺寸等
+3. 控制窗口动画
+4. 输入事件分发
+
+#### 总结
+
+![](https://i.loli.net/2020/03/23/X2pw9F6B5SmdVRj.png)
+