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