自己看源码后的学习记录，仅供参考。

【Android】Activity/Window/DecorView/ViewRootImpl的创建时机1.Activity 的创建时机-> public static void main(String[] args)-> ActivityThread.performLaunchActivity（）//	Activity 被创建的时候会调用 performLaunchActivity 方法-> Activity activity = null;// 在 performLaunchActivity 方法内部，通过类加载器创建 Activity 实例java.lang.ClassLoader cl = appContext.getClassLoader();activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);
3.Window 的创建时机-> ActivityThread.performLaunchActivity（）-> Activity.attach() // performLaunchActivity 方法内部调用了 attach-> mWindow = new PhoneWindow(this, window, activityConfigCallback);  // Activity 中的成员变量 mWindow-> mDecor = (DecorView) preservedWindow.getDecorView(); 
4.DecorView 的创建时机onCreate 中调用 setContentView 方法AppcompatActivity.setContentView ->AppCompatDelegateImpl.setContentView ->AppCompatDelegateImpl.ensureSubDecor ->AppCompatDelegateImpl.createSubDecor ->Window.getDecorView -> // Window 是个抽象类，如下：// public abstract class Window // PhoneWindow 是 Window 的实现类，如下：// public class PhoneWindow extends Window implements MenuBuilder.Callback// Window.getDecorView()也就是 PhoneWindow.getDecorView()PhoneWindow.getDecorView ->// 下面是 PhoneWindow 中的 getDecorView 方法public class PhoneWindow extends Window implements MenuBuilder.Callback @Overridepublic final @NonNull View getDecorView() {if (mDecor == null || mForceDecorInstall) {installDecor();}return mDecor;}// installDecor 方法中创建 DecorView 对象，并与 Window 绑定-> installDecor() -> mDecor = generateDecor(-1);-> new DecorView(context, featureId, this, getAttributes());	-> mDecor.setWindow(this);5.绘制流程：
->ActivityThread.handleResumeActivity()->ViewManager.addView(decor, l); // ViewManager是接口 ，如下：  // public interface ViewManager// public interface WindowManager extends ViewManager // WindowManager 还是接口// public interface WindowManager extends ViewManager// WindowManagerImpl 是 WindowManager 的实现，所以：->WindowManager ->WindowManagerImpl ->WindowManagerGlobal 的addView（）ViewRootImpl是在WindowManagerGlobal的addView方法中被初始化的
并且也是在这里与DecorView进行绑定，成为DecorView的parent-> addView()-> root = new ViewRootImpl(view.getContext(), display);view.setLayoutParams(wparams);mViews.add(view);mRoots.add(root);mParams.add(wparams);// do this last because it fires off messages to start doing thingstry {root.setView(view, wparams, panelParentView);在ViewRootImpl的setView方法中，又会调用requestLayout，在这里就会进行这个View树的第一次测绘。
具体的方式是通过scheduleTraversals方法向Choreographer发送一个预定的消息，
并在下一次屏幕刷新的时候调用doTraversal → performTraversals方法进行ViewTree的测量、布局和绘制。-> setView()-> requestLayout()-> scheduleTraversals()-> mChoreographer.postCallback(Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);-> doTraversal()-> performTraversals()-> performMeasure() / performLayout()/ performDraw()ViewManager、WindowManager、WindowManagerImpl、WindowManagerGlobal之间的关系public interface ViewManager{public void addView(View view, ViewGroup.LayoutParams params);public void updateViewLayout(View view, ViewGroup.LayoutParams params);public void removeView(View view);}public interface WindowManager extends ViewManager{......}public final class WindowManagerImpl implements WindowManager {private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();@overridepublic void addView(view,params){mGlobal.addView(...);}public void updateViewLayout(view,params){mGlobal.updateViewLayout(...);}public void remove(view){mGlobal.remove(...);}}public final class WindowManagerGlobal {public void addView(...){......}public void updateViewLayout(...) {......}public void removeView(...) {......}}