Window, WindowManager, WindowManagerService 的简单梳理（一）

Window, WindowManager, WindowManagerService 的简单梳理（二）- Window 的添加过程

相比前面两篇，Activiy 的 Window 的创建过程要简单多了。大致有下面几个步骤：

• PhoneWindow 的创建
  在 Activity 启动时，会通过 ActivityThread 的 performLaunchActivity() 启动对应 Activity。其中，就会调用 Activity 的 attach()方法。
  在 Activity 的 attach() 方法里面，可以看到创建了 PhoneWindow 对象。当然，PhoneWindow 并不是 WindowManagerService 添加的 Window，不是一个概念。关于 Window 的概念，见上面两篇文章。

   // Activity
   final void attach(Context context, ActivityThread aThread,
           Instrumentation instr, IBinder token, int ident,
           Application application, Intent intent, ActivityInfo info,
           CharSequence title, Activity parent, String id,
           NonConfigurationInstances lastNonConfigurationInstances,
           Configuration config, String referrer, IVoiceInteractor voiceInteractor,
           Window window) {
       attachBaseContext(context);
  
       mFragments.attachHost(null /*parent*/);
  
       mWindow = new PhoneWindow(this, window);
       mWindow.setWindowControllerCallback(this);
       mWindow.setCallback(this);
       mWindow.setOnWindowDismissedCallback(this);
       mWindow.getLayoutInflater().setPrivateFactory(this);
  
       ...
       mWindow.setWindowManager(
               (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
               mToken, mComponent.flattenToString(),
               (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
       if (mParent != null) {
           mWindow.setContainer(mParent.getWindow());
       }
       mWindowManager = mWindow.getWindowManager();
       mCurrentConfig = config;
   }
  

  顺便一提，Activity 实现了 Window.Callback 接口。

  // Window
   public interface Callback {
       public boolean dispatchKeyEvent(KeyEvent event);
       public boolean dispatchKeyShortcutEvent(KeyEvent event);
       public boolean dispatchTouchEvent(MotionEvent event);
       public boolean dispatchTrackballEvent(MotionEvent event);
       public boolean dispatchGenericMotionEvent(MotionEvent event);
       public boolean dispatchPopulateAccessibilityEvent(AccessibilityEvent event);
       public View onCreatePanelView(int featureId);
       public boolean onCreatePanelMenu(int featureId, Menu menu);
       public boolean onPreparePanel(int featureId, View view, Menu menu);
       public boolean onMenuOpened(int featureId, Menu menu);
       public boolean onMenuItemSelected(int featureId, MenuItem item);
       public void onWindowAttributesChanged(WindowManager.LayoutParams attrs);
       public void onContentChanged();
       public void onWindowFocusChanged(boolean hasFocus);
       public void onAttachedToWindow();
       public void onDetachedFromWindow();
       public void onPanelClosed(int featureId, Menu menu);
       public boolean onSearchRequested();
       public boolean onSearchRequested(SearchEvent searchEvent);
       public ActionMode onWindowStartingActionMode(ActionMode.Callback callback);
       public ActionMode onWindowStartingActionMode(ActionMode.Callback callback, int type);
       public void onActionModeStarted(ActionMode mode);
       public void onActionModeFinished(ActionMode mode);
       default public void onProvideKeyboardShortcuts(
               List<KeyboardShortcutGroup> data, @Nullable Menu menu, int deviceId) { };
  }
  

• DecorView 的创建
  ActivityThread 的 performLaunchActivity() 调用 attach() 之后，会调用到 Activity 的 onCreate。众所周知，我们是在 onCreate 里面 setContentView 的。

  // Activity
   public void setContentView(@LayoutRes int layoutResID) {
       getWindow().setContentView(layoutResID);
       initWindowDecorActionBar();
   }
  

  还是进入了 PhoneWindow。
  然后在 PhoneWindow 的 installDecor 中，用 generateDecor 中创建了 DecorView mDecor；用 generateLayout 创建了 mContentParent。我们设置的 Activity 的布局就是最终加入 mContentParent 中进行显示。

  // PhoneWindow
      // This is the top-level view of the window, containing the window decor.
      private DecorView mDecor;
  
      // This is the view in which the window contents are placed. It is either
      // mDecor itself, or a child of mDecor where the contents go.
      ViewGroup mContentParent;
  
      public void setContentView(int layoutResID) {
       // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window
       // decor, when theme attributes and the like are crystalized. Do not check the feature
       // before this happens.
       if (mContentParent == null) {
           // 内部会初始化 mDecor 和 mContentParent
           installDecor();
       } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
           mContentParent.removeAllViews();
       }
  
       if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
           final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                   getContext());
           transitionTo(newScene);
       } else {
           // 将设置的 Activity 的 Layout 添加到 mContentParent 上面
           mLayoutInflater.inflate(layoutResID, mContentParent);
       }
       mContentParent.requestApplyInsets();
       // 这里的 cb 就是 Activity attach() 的时候传入的 Activity 对象
       final Callback cb = getCallback();
       if (cb != null && !isDestroyed()) {
           cb.onContentChanged();
       }
       mContentParentExplicitlySet = true;
   }
  
      private void installDecor() {
          mForceDecorInstall = false;
          if (mDecor == null) {
              // 生成 mDecor
              mDecor = generateDecor(-1);
              mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
              mDecor.setIsRootNamespace(true);
              if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
                  mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
              }
          } else {
              mDecor.setWindow(this);
          }
          if (mContentParent == null) {
              // 生成 mContentParent 
              mContentParent = generateLayout(mDecor);
  
              // Set up decor part of UI to ignore fitsSystemWindows if appropriate.
              mDecor.makeOptionalFitsSystemWindows();
  
              final DecorContentParent decorContentParent = (DecorContentParent) mDecor.findViewById(
                   R.id.decor_content_parent);
              ...
          }
      }
  
      protected DecorView generateDecor(int featureId) {
          // System process doesn't have application context and in that case we need to directly use
          // the context we have. Otherwise we want the application context, so we don't cling to the
          // activity.
          Context context;
          ...
          return new DecorView(context, featureId, this, getAttributes());
       }
  
      public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;
  
      protected ViewGroup generateLayout(DecorView decor) {
          // Apply data from current theme.
          ...
          ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
          ...
          return contentParent;
      }
  

• 添加 DecorView 到 WindowManager
  《Android 开发艺术探索》对于这个阶段说的很有道理，这个时候 DecorView 还没有被 WindowManager 识别，所以这个时候 Window 还无法提供具体功能，因为它还无法接收外界的输入信息。
  DecorView 是在 Activity 的 onResume 阶段添加到 WindowManager 的。
  具体是在 ActivityThread 的 handleResumeActivity() 方法中触发了添加 DecorView 到 WindowManager 的代码调用，并且是在调用了 onResume() 方法之后。
  所以我在 Activity 的 onStart() 和 onResume() 中做了测试：可以 get 到 DecorView，但是 DecorView 的 isAttachedToWindow() 返回的是 false。

  // ActivityThread 
      final void handleResumeActivity(IBinder token,
              boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {
          ActivityClientRecord r = mActivities.get(token);
          if (!checkAndUpdateLifecycleSeq(seq, r, "resumeActivity")) {
              return;
          }
          ...
          // TODO Push resumeArgs into the activity for consideration
          // performResumeActivity 会触发 Activity onResume 的调用
          r = performResumeActivity(token, clearHide, reason);
  
          if (r != null) {
              final Activity a = r.activity;
              ...
              // 下面这段代码就是将 DecorView 添加到 WindowManager
              if (r.window == null && !a.mFinished && willBeVisible) {
                  r.window = r.activity.getWindow();
                  View decor = r.window.getDecorView();
                  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) {
                      a.mWindowAdded = true;
                      wm.addView(decor, l);
                  }
  
              // If the window has already been added, but during resume
              // we started another activity, then don't yet make the
              // window visible.
              } else if (!willBeVisible) {
                  if (localLOGV) Slog.v(
                      TAG, "Launch " + r + " mStartedActivity set");
                  r.hideForNow = true;
              }
  
              ...
              // 代码中还有一个分支会调用到 Activity 的 makeVisible()，这里我就直接省略掉了。
             // 但是我们可以看一下 Activity 的 makeVisible() 方法的实现
      }
  
  // Activity
      void makeVisible() {
          if (!mWindowAdded) {
              ViewManager wm = getWindowManager();
              wm.addView(mDecor, getWindow().getAttributes());
              mWindowAdded = true;
          }
          mDecor.setVisibility(View.VISIBLE);
      }
  

可见，Activity 的显示，最终也是将一个 View 添加到 WindowManager 之中。只不过这里是 DecorView，但是接下来的方法和流程与 Window, WindowManager, WindowManagerService 的简单梳理（二）- Window 的添加过程 中介绍的相同。

不仅 Activity 如此，Dialog 和 Toast 最终也是将一个 View 添加到 WindowManager 中，最终实现自己的显示窗口的添加，以完成显示功能。