【Android】Android Window

1，Window和View的关系

View必须依托于Window这个抽象该类存在，通过Window实现View的变化，

Activity的启动过程，View和Window的联系发生在ActivityThread的handleResumeActivity函数中，

通过makeVisible，使得界面对用户可见

if (r.activity.mVisibleFromClient) {     r.activity.makeVisible(); }

可以看到，wm在此处才添加mDecor(顶层View)

void makeVisible() { if (!mWindowAdded) { ViewManager wm = getWindowManager(); wm.addView(mDecor, getWindow().getAttributes()); mWindowAdded = true; } mDecor.setVisibility(View.VISIBLE); }

简而言之： Activity ---- Window ---- View

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2，WindowManager.addView()分析

在Activity中，通过Context可以获取到WindowManager，

val wm: WindowManager = this.getSystemService(Context.WINDOW_SERVICE) as WindowManager

wm提供三种核心方法，即View的add、update、delete，继承ViewManager，

public interface ViewManager {     /**      * Assign the passed LayoutParams to the passed View and add the view to the window.      * <p>Throws {@link android.view.WindowManager.BadTokenException} for certain programming      * errors, such as adding a second view to a window without removing the first view.      * <p>Throws {@link android.view.WindowManager.InvalidDisplayException} if the window is on a      * secondary {@link Display} and the specified display can't be found      * (see {@link android.app.Presentation}).      * @param view The view to be added to this window.      * @param params The LayoutParams to assign to view.      */     public void addView(View view, ViewGroup.LayoutParams params);     public void updateViewLayout(View view, ViewGroup.LayoutParams params);     public void removeView(View view); }

而具体实现类是WindowManagerImpl，现在可以先分析下addView方法，注意WindowManager只有一个实现类WindowManagerImpl，

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

委托给WindowManagerGlobal实现，

public void addView(View view, ViewGroup.LayoutParams params,         Display display, Window parentWindow, int userId) {     if (view == null) {         throw new IllegalArgumentException("view must not be null");     }     if (display == null) {         throw new IllegalArgumentException("display must not be null");     }     if (!(params instanceof WindowManager.LayoutParams)) {         throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");     }     final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;     if (parentWindow != null) {          //对子window，调整参数         parentWindow.adjustLayoutParamsForSubWindow(wparams);     } else {         // If there's no parent, then hardware acceleration for this view is         // set from the application's hardware acceleration setting.         final Context context = view.getContext();         if (context != null                 && (context.getApplicationInfo().flags                         & ApplicationInfo.FLAG_HARDWARE_ACCELERATED) != 0) {             wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;         }     }     ViewRootImpl root;     View panelParentView = null;     synchronized (mLock) {         // Start watching for system property changes.         if (mSystemPropertyUpdater == null) {             mSystemPropertyUpdater = new Runnable() {                 @Override public void run() {                     synchronized (mLock) {                         for (int i = mRoots.size() - 1; i >= 0; --i) {                             mRoots.get(i).loadSystemProperties();                         }                     }                 }             };             SystemProperties.addChangeCallback(mSystemPropertyUpdater);         }         int index = findViewLocked(view, false);         if (index >= 0) {             if (mDyingViews.contains(view)) {                 // Don't wait for MSG_DIE to make it's way through root's queue.                 mRoots.get(index).doDie();             } else {                 throw new IllegalStateException("View " + view                         + " has already been added to the window manager.");             }             // The previous removeView() had not completed executing. Now it has.         }         // If this is a panel window, then find the window it is being         // attached to for future reference.         if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&                 wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {             final int count = mViews.size();             for (int i = 0; i < count; i++) {                 if (mRoots.get(i).mWindow.asBinder() == wparams.token) {                     panelParentView = mViews.get(i);                 }             }         }         root = new ViewRootImpl(view.getContext(), display);         view.setLayoutParams(wparams);         // 这是存储了所有Window的参数，严格按照顺序         mViews.add(view);         mRoots.add(root);         mParams.add(wparams);         // do this last because it fires off messages to start doing things         try {             //再次委托给ViewRootImpl完成界面添加过程             root.setView(view, wparams, panelParentView, userId);         } catch (RuntimeException e) {             // BadTokenException or InvalidDisplayException, clean up.             if (index >= 0) {                 removeViewLocked(index, true);             }             throw e;         }     } }

调用ViewRootImpl的setView方法继续该过程，

该方法内部调用requestLayout，进入三大过程，在此不展开分析，

@Override public void requestLayout() {     if (!mHandlingLayoutInLayoutRequest) {         checkThread();         mLayoutRequested = true;         scheduleTraversals();     } }

最终通过mWindowSession(IWindowSession)完成添加过程，这是一次IPC过程。

res = mWindowSession.addToDisplayAsUser(mWindow, mSeq, mWindowAttributes,         getHostVisibility(), mDisplay.getDisplayId(), userId, mTmpFrame,         mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,         mAttachInfo.mDisplayCutout, inputChannel,         mTempInsets, mTempControls); /**  * IWindowSession implementation. Currently this class doesn't need to support for multi-user.  */ @Override public int addToDisplayAsUser(IWindow window, int seq, WindowManager.LayoutParams attrs,         int viewVisibility, int displayId, int userId, Rect outFrame,         Rect outContentInsets, Rect outStableInsets,         DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel,         InsetsState outInsetsState, InsetsSourceControl[] outActiveControls) {     return addToDisplay(window, seq, attrs, viewVisibility, displayId,             outFrame, outContentInsets, outStableInsets, outDisplayCutout, outInputChannel,             outInsetsState, outActiveControls); }​

这样，Session内部通过WindowManagerService来实现了Window的添加。
WindowManagerService会为每个应用保存一个单独的Session。

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3，WindowManager的使用

通过自定义一个Activity来使用wm提供的api，如下所示：

override fun onCreate(savedInstanceState: Bundle?) {     super.onCreate(savedInstanceState)     setContentView(R.layout.activity_main2)     val button: Button = findViewById(R.id.button_2)     // 这里初始化layoutParams，注意必须是WindowManager.LayoutParams     mLayoutParams = WindowManager.LayoutParams(         ViewGroup.LayoutParams.WRAP_CONTENT,         ViewGroup.LayoutParams.WRAP_CONTENT,         WindowManager.LayoutParams.TYPE_APPLICATION, //窗口类型，z-order的依据         0,  //flag         PixelFormat.TRANSPARENT     )     // 这些flag定义了窗口的特性     mLayoutParams.flags =         WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL or                 WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE or                 WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED     //组件对齐方式     mLayoutParams.gravity = Gravity.LEFT or Gravity.TOP     // 组件位置     mLayoutParams.x = 100     mLayoutParams.y = 300     val wm: WindowManager = this.getSystemService(Context.WINDOW_SERVICE) as WindowManager     mTextView = TextView(this)     mTextView.text = "I am TextView"     // 直接addView     wm.addView(mTextView, mLayoutParams)          mTextView.setOnTouchListener(this) }

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4，Window的创建过程

对于Activity，在其attach()方法中，

mWindow = new PhoneWindow(this, window, activityConfigCallback); mWindow.setWindowControllerCallback(mWindowControllerCallback); mWindow.setCallback(this); mWindow.setOnWindowDismissedCallback(this); mWindow.getLayoutInflater().setPrivateFactory(this);

这里直接创建了一个PhoneWindow，如何设置一系列回调，如下：

private final WindowControllerCallback mWindowControllerCallback =         new WindowControllerCallback(){ /**  * Moves the activity between {@link WindowConfiguration#WINDOWING_MODE_FREEFORM} windowing  * mode and {@link WindowConfiguration#WINDOWING_MODE_FULLSCREEN}.  *  * @hide  */  @Override  public void toggleFreeformWindowingMode() throws RemoteException { ActivityTaskManager.getService().toggleFreeformWindowingMode(mToken);  } /**  * Puts the activity in picture-in-picture mode if the activity supports.  * @see android.R.attr#supportsPictureInPicture  * @hide  */  @Override  public void enterPictureInPictureModeIfPossible() { if (mActivityInfo.supportsPictureInPicture()) { enterPictureInPictureMode();  } } @Override  public boolean isTaskRoot() { try { return ActivityTaskManager.getService().getTaskForActivity(mToken, true) >= 0;  } catch (RemoteException e) { return false;  } } /**  * Update the forced status bar color.  * @hide  */  @Override  public void updateStatusBarColor(int color) { mTaskDescription.setStatusBarColor(color);  setTaskDescription(mTaskDescription);  } /**  * Update the forced navigation bar color.  * @hide  */  @Override  public void updateNavigationBarColor(int color) { mTaskDescription.setNavigationBarColor(color);  setTaskDescription(mTaskDescription);  } }

对于Dialog和Toast，创建过程类似，

比如Dialog的构造函数，

Dialog(@NonNull Context context, @StyleRes int themeResId, boolean createContextThemeWrapper) {     if (createContextThemeWrapper) {         if (themeResId == Resources.ID_NULL) {             final TypedValue outValue = new TypedValue();             context.getTheme().resolveAttribute(R.attr.dialogTheme, outValue, true);             themeResId = outValue.resourceId;         }         mContext = new ContextThemeWrapper(context, themeResId);     } else {         mContext = context;     }     mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);     final Window w = new PhoneWindow(mContext);     mWindow = w;     w.setCallback(this);     w.setOnWindowDismissedCallback(this);     w.setOnWindowSwipeDismissedCallback(() -> {         if (mCancelable) {             cancel();         }     });     w.setWindowManager(mWindowManager, null, null);     w.setGravity(Gravity.CENTER);     mListenersHandler = new ListenersHandler(this); }