Android进阶基础系列：Window和WindowManager ，全面理解！

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hfy胡飞洋 2022-01-11 16:12:09 ©著作权

文章标签 Android android ide java 文章分类 代码人生

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Window，表示一个窗口的抽象的概念；同时也是一个抽象类，唯一的实现是PhoneWindow。在PhoneWindow中有一个顶级View—DecorView，继承自FrameLayout，我们可以通过getDecorView()获得它，当我们调用Activity的setContentView时，其实最终会调用Window的setContentView，当我们调用Activity的findViewById时，其实最终调用的是Window的findViewById，这也间接的说明了Window是View的直接管理者。但是Window并不是真实存在的，它更多的表示一种抽象的功能集合，View才是Android中的视图呈现形式，绘制到屏幕上的是View不是Window，但是View不能单独存在，它必需依附在Window这个抽象的概念上面，Android中需要依赖Window提供视图的有Activity，Dialog，Toast，PopupWindow，StatusBarWindow（系统状态栏），输入法窗口等，因此Activity，Dialog等视图都对应着一个Window。
创建Window，通过WindowManager即可完成。WindowManager是操作Window的入口，Window的具体实现是在WindowManagerService中。WindowManager和WindowManagerService交互是IPC（跨进程通信）过程。

Window是View的管理者，当我们说创建Window时，一方面指实例化这个管理者，一方面指用WindowManager.addView()添加view，以view的形式来呈现Window这个概念。

一、Window和WindowManager

1.1 window

先看创建window的代码

WindowManager windowManager = getWindowManager();
        Button view = new Button(this);
        view.setText("添加到window中的button");

        WindowManager.LayoutParams layoutParams = new WindowManager.LayoutParams();

        layoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
                | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL
                | WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED;
        layoutParams.type = WindowManager.LayoutParams.TYPE_APPLICATION;

        layoutParams.format = PixelFormat.TRANSPARENT;
        layoutParams.gravity = Gravity.TOP | Gravity.LEFT;
        layoutParams.x = 100;
        layoutParams.y = 100;
        layoutParams.width = ViewGroup.LayoutParams.WRAP_CONTENT;
        layoutParams.height = ViewGroup.LayoutParams.WRAP_CONTENT;

        windowManager.addView(view, layoutParams);
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Android进阶基础系列：Window和WindowManager ，全面理解！_java 实际就只有一句windowManager.addView(view, layoutParams)，这样就添加了一个Window，这个window只有一个button。看下LayoutParams的两个不太认识的属性，flags、type。 flags，决定window的显示特性，有很多值，看下常用的：

FLAG_NOT_FOCUSABLE，不需要获取焦点、不需要输入事件，同时会自定开启FLAG_NOT_TOUCH_MODAL，最终事件会传递给下层具有焦点的window。

FLAG_NOT_TOUCH_MODAL，window区域以外的单击事件会传递给下层window，window范围内的事件自己处理。一般需要开启此标记，否则其他window不能收到事件。

FLAG_SHOW_WHEN_LOCKED，开启后可以让window显示在锁屏的界面上。

type参数表示window的类型。window有三种类型，应用window、子window、系统window。应用window对应activity；子window要依附在父window上，如dialog；系统window需要申明权限才能创建，比如toast、系统状态栏。 window是分层的，每个window都有对应的z-ordered，层级大的在层级小的上层。应用window的层级范围是1-99，子window是1000-1999，系统window是2000-2999，即type的值。

如果想window位于所有window顶层，那就用系统window。可以设置layoutParams.type = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY，并且，要申明使用权限，且6.0以后要让用户手动打开权限。

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/>
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否则会报错：

Caused by: android.view.WindowManager$BadTokenException: Unable to add window android.view.ViewRootImpl$W@305c3bc -- permission denied for window type 2038
        at android.view.ViewRootImpl.setView(ViewRootImpl.java:958)
        at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:398)
        at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:131)
        at com.hfy.demo01.MainActivity.initCustomWindow(MainActivity.java:266)
        at com.hfy.demo01.MainActivity.initView(MainActivity.java:170)
        at com.hfy.demo01.MainActivity.onCreate(MainActivity.java:116)
        at android.app.Activity.performCreate(Activity.java:7458)
        at android.app.Activity.performCreate(Activity.java:7448)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1286)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3409)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3614) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:86) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2199) 
        at android.os.Handler.dispatchMessage(Handler.java:112) 
        at android.os.Looper.loop(Looper.java:216) 
        at android.app.ActivityThread.main(ActivityThread.java:7625) 

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使用系统window的完整代码：

private void initCustomWindow() {
        //6.0以上需要用户手动打开权限
        // (SYSTEM_ALERT_WINDOW and WRITE_SETTINGS, 这两个权限比较特殊，
        // 不能通过代码申请方式获取，必须得用户打开软件设置页手动打开，才能授权。Manifest申请该权限是无效的。)
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M){
            if (!Settings.canDrawOverlays(this)) {
                //打开设置页，让用户打开设置
                Toast.makeText(this, "can not DrawOverlays", Toast.LENGTH_SHORT).show();
                Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, Uri.parse("package:" + MainActivity.this.getPackageName()));
                startActivityForResult(intent, OVERLAY_PERMISSION_REQ_CODE);
            }else {
                //已经打开了权限
                handleAddWindow();
            }
        }else {
            //6.0以下直接 Manifest申请该权限 就行。
            handleAddWindow();
        }
    }

    private void handleAddWindow() {
        Button view = new Button(this);
        view.setText("添加到window中的button");

        WindowManager.LayoutParams layoutParams = new WindowManager.LayoutParams(
                WindowManager.LayoutParams.WRAP_CONTENT,
                WindowManager.LayoutParams.WRAP_CONTENT,
                0, 0,
                PixelFormat.TRANSPARENT
        );
        // flag 设置 Window 属性
        layoutParams.flags= WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL;
        // type 设置 Window 类别（层级）：系统window
        layoutParams.type = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY;

        layoutParams.gravity = Gravity.TOP | Gravity.LEFT;
        layoutParams.x = 100;
        layoutParams.y = 100;

        WindowManager windowManager = getWindowManager();
        windowManager.addView(view, layoutParams);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        switch (requestCode){
            case OVERLAY_PERMISSION_REQ_CODE:
                if (Settings.canDrawOverlays(this)) {
                    //打开了权限
                    handleAddWindow();
                }else {
                    Toast.makeText(this, "can not DrawOverlays", Toast.LENGTH_SHORT).show();
                }
                break;
            default:
                break;
        }
    }
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按home键后效果： Android进阶基础系列：Window和WindowManager ，全面理解！_Android_02

1.2 WindowManager

WindowManager是个接口，继承自ViewManager：

public interface ViewManager{
    public void addView(View view, ViewGroup.LayoutParams params);
    public void updateViewLayout(View view, ViewGroup.LayoutParams params);
    public void removeView(View view);
}
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所以，windowManager就是添加、更新、删除 view，实际使用的就是这三个方法，上面创建window的例子用的就是addView方法。所以，操作window就是操作view。

二、window的内部机制

window是抽象的概念，在视图中不是实际存在，它以view的形式呈现。一个window就对应一个view，window操作view实际是通过ViewRootImpl实现。使用中是通过WindowManager对的操作，无法直接访问window。下面就看看WindowManager的三个方法。

2.1 window的添加

WindowManager的实现类是WindowManagerImpl，那么看看操作view的三个方法的实现：

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

    @Override
    public void updateViewLayout(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
        applyDefaultToken(params);
        mGlobal.updateViewLayout(view, params);
    }

    @Override
    public void removeView(View view) {
        mGlobal.removeView(view, false);
    }
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可以看到，全都交给mGlobal处理了，那看下mGlobal，是个单例对象：

private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();
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public static WindowManagerGlobal getInstance() {
        synchronized (WindowManagerGlobal.class) {
            if (sDefaultWindowManager == null) {
                sDefaultWindowManager = new WindowManagerGlobal();
            }
            return sDefaultWindowManager;
        }
    }
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那么来看下mGlobal.addView，具体简要概括为3个步骤：

数据检查
更新各种参数列表
RootViewImpl添加view（含window的添加）

public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
        //1、数据检查
        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) {
            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;
        ...
            //创建viewRoot（一个window对应一个viewRoot）
            root = new ViewRootImpl(view.getContext(), display);
            view.setLayoutParams(wparams);

            //2、更新各种参数列：所有window的--view的列表、rootView的列表、view参数的列表
            mViews.add(view);
            mRoots.add(root);
            mParams.add(wparams);

            // do this last because it fires off messages to start doing things
            try {
                // 3、RootViewImpl添加view（含window的添加）
                root.setView(view, wparams, panelParentView);
            } catch (RuntimeException e) {
                // BadTokenException or InvalidDisplayException, clean up.
                if (index >= 0) {
                    removeViewLocked(index, true);
                }
                throw e;
            }
        }
    }
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接着看ViewRootImpl的setView：

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
        ...
        //1.绘制view
        requestLayout();

                if ((mWindowAttributes.inputFeatures
                        & WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
                    mInputChannel = new InputChannel();
                }
                mForceDecorViewVisibility = (mWindowAttributes.privateFlags
                        & PRIVATE_FLAG_FORCE_DECOR_VIEW_VISIBILITY) != 0;
                try {
                    mOrigWindowType = mWindowAttributes.type;
                    mAttachInfo.mRecomputeGlobalAttributes = true;
                    collectViewAttributes();
                    //2.通过session与WMS建立通信：完成window的添加
                    res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                            getHostVisibility(), mDisplay.getDisplayId(), mWinFrame,
                            mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                            mAttachInfo.mOutsets, mAttachInfo.mDisplayCutout, mInputChannel);
                } catch (RemoteException e) {
                    mAdded = false;
                    mView = null;
                    mAttachInfo.mRootView = null;
                    mInputChannel = null;
                    mFallbackEventHandler.setView(null);
                    unscheduleTraversals();
                    setAccessibilityFocus(null, null);
                    throw new RuntimeException("Adding window failed", e);
                }
        ...
}
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两个步骤：1、调用requestLayout()异步刷新view，2、mWindowSession.addToDisplay()完成window的添加。

requestLayout()内部最后走到performTraversals()，我们知道这是view绘制流程入口。如下所示：

@Override
    public void requestLayout() {
        if (!mHandlingLayoutInLayoutRequest) {
            checkThread();
            mLayoutRequested = true;
            scheduleTraversals();
        }
    }
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void scheduleTraversals() {
        if (!mTraversalScheduled) {
            mTraversalScheduled = true;
            mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
            mChoreographer.postCallback(
                    Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
            if (!mUnbufferedInputDispatch) {
                scheduleConsumeBatchedInput();
            }
            notifyRendererOfFramePending();
            pokeDrawLockIfNeeded();
        }
    }
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final class TraversalRunnable implements Runnable {
        @Override
        public void run() {
            doTraversal();
        }
    }
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void doTraversal() {
        if (mTraversalScheduled) {
            mTraversalScheduled = false;
            mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);

            if (mProfile) {
                Debug.startMethodTracing("ViewAncestor");
            }
            // 绘制流程
            performTraversals();

            if (mProfile) {
                Debug.stopMethodTracing();
                mProfile = false;
            }
        }
    }
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至于mWindowSession.addToDisplay()，先看mWindowSession，类型是IWindowSession，是个Binder对象，具体是com.android.server.wm.Session，所以window的添加是一个IPC过程。mWindowSessionde 是在ViewRootImpl创建时获取，由WindowManagerGlobal通过获取WindowManagerService来为每个应用创建一个单独的session。

public ViewRootImpl(Context context, Display display) {
        mContext = context;
        mWindowSession = WindowManagerGlobal.getWindowSession();
  ...
}
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public static IWindowSession getWindowSession() {
        synchronized (WindowManagerGlobal.class) {
            if (sWindowSession == null) {
                try {
                    InputMethodManager imm = InputMethodManager.getInstance();
                    IWindowManager windowManager = getWindowManagerService();
                    sWindowSession = windowManager.openSession(
                            new IWindowSessionCallback.Stub() {
                                @Override
                                public void onAnimatorScaleChanged(float scale) {
                                    ValueAnimator.setDurationScale(scale);
                                }
                            },
                            imm.getClient(), imm.getInputContext());
                } catch (RemoteException e) {
                    throw e.rethrowFromSystemServer();
                }
            }
            return sWindowSession;
        }
    }
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public static IWindowManager getWindowManagerService() {
        synchronized (WindowManagerGlobal.class) {
            if (sWindowManagerService == null) {
                sWindowManagerService = IWindowManager.Stub.asInterface(
                        ServiceManager.getService("window"));
                try {
                    if (sWindowManagerService != null) {
                        ValueAnimator.setDurationScale(
                                sWindowManagerService.getCurrentAnimatorScale());
                    }
                } catch (RemoteException e) {
                    throw e.rethrowFromSystemServer();
                }
            }
            return sWindowManagerService;
        }
    }
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然后是WindowManagerService的openSession：

@Override
    public IWindowSession openSession(IWindowSessionCallback callback, IInputMethodClient client,
            IInputContext inputContext) {
        if (client == null) throw new IllegalArgumentException("null client");
        if (inputContext == null) throw new IllegalArgumentException("null inputContext");
        Session session = new Session(this, callback, client, inputContext);
        return session;
    }
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接着看Session的addToDisplay：

@Override
    public int addToDisplay(IWindow window, int seq, WindowManager.LayoutParams attrs,
            int viewVisibility, int displayId, Rect outFrame, Rect outContentInsets,
            Rect outStableInsets, Rect outOutsets,
            DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel) {
        return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId, outFrame,
                outContentInsets, outStableInsets, outOutsets, outDisplayCutout, outInputChannel);
    }
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window的添加就交给WindowManagerService了。 WindowManagerService主要作用：

窗口管理：是先进行窗口的权限检查，因为系统窗口需要声明权限，然后根据相关的Display信息以及窗口信息对窗口进行校对，再然后获取对应的WindowToken，再根据不同的窗口类型检查窗口的有效性，如果上面一系列步骤都通过了，就会为该窗口创建一个WindowState对象，以维护窗口的状态和根据适当的时机调整窗口状态，最后就会通过WindowState的attach方法与SurfaceFlinger通信。因此SurfaceFlinger能使用这些Window信息来合成surfaces,并渲染输出到显示设备。

输入事件的中转站：当我们的触摸屏幕时就会产生输入事件，在Android中负责管理事件的输入是InputManagerService，它里面有一个InputManager，在启动IMS的同时会创建InputManager，在创建InputManager同时创建InputReader和InputDispatcher，InputReader会不断的从设备节点中读取输入事件，InputReader将这些原始输入事件加工后就交给InputDispatcher，而InputDispatcher它会寻找一个最合适的窗口来处理输入事件，WMS是窗口的管理者，WMS会把所有窗口的信息更新到InputDispatcher中，这样InputDispatcher就可以将输入事件派发给合适的Window，Window就会把这个输入事件传给顶级View，然后就会涉及我们熟悉的事件分发机制。

2.2 window的更新

直接看mGlobal.updateViewLayout(view, params)：

public void updateViewLayout(View view, ViewGroup.LayoutParams params) {
        //1、参数检查
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }
        if (!(params instanceof WindowManager.LayoutParams)) {
            throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
        }

        final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;
        //2、更新layoutParams及参数列表列表
        view.setLayoutParams(wparams);
        synchronized (mLock) {
            int index = findViewLocked(view, true);
            ViewRootImpl root = mRoots.get(index);
            mParams.remove(index);
            mParams.add(index, wparams);
            //3、RootViewImpl更新布局
            root.setLayoutParams(wparams, false);
        }
    }
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再看ViewRootIml.setLayoutParams()中会调用scheduleTraversals() 重新绘制布局，其中也会调用mWindowSession.relayout来更新window ，也是IPC过程。

2.3 window 删除

直接看mGlobal.removeView(view, false)：

public void removeView(View view, boolean immediate) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }

        synchronized (mLock) {
            //找到要移除view在列表中的index
            int index = findViewLocked(view, true);
            View curView = mRoots.get(index).getView();
            //移除
            removeViewLocked(index, immediate);
            if (curView == view) {
                return;
            }

            throw new IllegalStateException("Calling with view " + view
                    + " but the ViewAncestor is attached to " + curView);
        }
    }
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再看removeViewLocked(index, immediate)：

private void removeViewLocked(int index, boolean immediate) {
        //找到对应的ViewRoot
        ViewRootImpl root = mRoots.get(index);
        View view = root.getView();

        if (view != null) {
            InputMethodManager imm = InputMethodManager.getInstance();
            if (imm != null) {
                imm.windowDismissed(mViews.get(index).getWindowToken());
            }
        }
        //ViewRoot用die来删除
        boolean deferred = root.die(immediate);
        if (view != null) {
            view.assignParent(null);
            if (deferred) {
                //记录要删除的view
                mDyingViews.add(view);
            }
        }
    }
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继续看root.die(immediate)：

boolean die(boolean immediate) {
        // 如果是立刻删除，直接调doDie()
        if (immediate && !mIsInTraversal) {
            doDie();
            return false;
        }

        if (!mIsDrawing) {
            destroyHardwareRenderer();
        } else {
            Log.e(mTag, "Attempting to destroy the window while drawing!\n" +
                    "  window=" + this + ", title=" + mWindowAttributes.getTitle());
        }
        //不是立刻删，就放入队列
        mHandler.sendEmptyMessage(MSG_DIE);
        return true;
    }
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继续看doeDie()：

void doDie() {
        checkThread();
        if (LOCAL_LOGV) Log.v(mTag, "DIE in " + this + " of " + mSurface);
        synchronized (this) {
            if (mRemoved) 
                return;
            }
            mRemoved = true;
            if (mAdded) {
                //删除操作
                dispatchDetachedFromWindow();
            }

            ...
         //移除对应列表中的root、view、param、dyingView
        WindowManagerGlobal.getInstance().doRemoveView(this);
    }
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看下dispatchDetachedFromWindow()：

void dispatchDetachedFromWindow() {
        mFirstInputStage.onDetachedFromWindow();
        if (mView != null && mView.mAttachInfo != null) {
            mAttachInfo.mTreeObserver.dispatchOnWindowAttachedChange(false);
            //回调view的dispatchDetachedFromWindow方法，意思是view要从window中移除了。一般可在其中做一些资源回收工作，如 停止动画等。
            mView.dispatchDetachedFromWindow();
        }
        //移除各种回调
        mAccessibilityInteractionConnectionManager.ensureNoConnection();
        mAccessibilityManager.removeAccessibilityStateChangeListener(
                mAccessibilityInteractionConnectionManager);
        mAccessibilityManager.removeHighTextContrastStateChangeListener(
                mHighContrastTextManager);
        removeSendWindowContentChangedCallback();

        destroyHardwareRenderer();

        setAccessibilityFocus(null, null);

        mView.assignParent(null);
        mView = null;
        mAttachInfo.mRootView = null;

        mSurface.release();

        if (mInputQueueCallback != null && mInputQueue != null) {
            mInputQueueCallback.onInputQueueDestroyed(mInputQueue);
            mInputQueue.dispose();
            mInputQueueCallback = null;
            mInputQueue = null;
        }
        if (mInputEventReceiver != null) {
            mInputEventReceiver.dispose();
            mInputEventReceiver = null;
        }
        try {
            //删除window
            mWindowSession.remove(mWindow);
        } catch (RemoteException e) {
        }

        // Dispose the input channel after removing the window so the Window Manager
        // doesn't interpret the input channel being closed as an abnormal termination.
        if (mInputChannel != null) {
            mInputChannel.dispose();
            mInputChannel = null;
        }

        mDisplayManager.unregisterDisplayListener(mDisplayListener);

        unscheduleTraversals();
    }
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好了，window的三个view操作就这些了。

三、常见Window的创建过程

View依附于Window这个抽象概念，有Activity、Dialog、Toast、PopupWindow等。

3.1 Activity的Window创建

Activity的启动略复杂，这里先看ActivityThread里的performLaunchActivity()：

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
    ...
    //创建activity实例：通过类加载器创建
    java.lang.ClassLoader cl = appContext.getClassLoader();
    activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);
    ...
    //调用Activity的attach方法--关联上下文环境变量
    activity.attach(appContext, this, getInstrumentation(), r.token,
                        r.ident, app, r.intent, r.activityInfo, title, r.parent,
                        r.embeddedID, r.lastNonConfigurationInstances, config,
                        r.referrer, r.voiceInteractor, window, r.configCallback);    
    ...
}
复制代码

接着看activity.attach方法：

//实例化window，就是Window的唯一实现PhoneWindow
        mWindow = new PhoneWindow(this, window, activityConfigCallback);
        ...
        //把activity作为回调接口传入window，这样window从外界接受的状态变化都会交给activity
        //例如：dispatchTouchEvent、onAttachedToWindow、onDetachedFromWindow
        mWindow.setCallback(this);
        ...
        //设置windowManager，实际就是WindowManagerImpl的实例，在activity中getWindowManager()获取的就是这个实例
        mWindow.setWindowManager(
                (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
                mToken, mComponent.flattenToString(),
                (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
        ...
        mWindowManager = mWindow.getWindowManager();
复制代码

OK，activity视图的管理者window已创建，那么什么时候用windowManager.addView() 来把activity的视图依附在window上呢？

先看Activity的setContentView方法，我们activity的视图由此方法设置：

public void setContentView(@LayoutRes int layoutResID) {
        getWindow().setContentView(layoutResID);
        initWindowDecorActionBar();
    }
复制代码

接着看PhonrWindow的setContentView：

public void setContentView(int layoutResID) {
        // mContentParent为空，就调installDecor()，猜想installDecor()里面创建了mContentParent。且从名字看出mContentParent就是内容视图的容器
        if (mContentParent == null) {
            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 {
            //这里看到，确实把我们的视图加载到mContentParent了
            mLayoutInflater.inflate(layoutResID, mContentParent);
        }
        ...
    }
复制代码

那就看installDecor():

private void installDecor() {
   if (mDecor == null) {
         //创建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) {
         //创建mContentParent
            mContentParent = generateLayout(mDecor);
   ...
}
复制代码

看下generateDecor(-1)，就是new了个DecorView：

protected DecorView generateDecor(int featureId) {
        Context context;
        if (mUseDecorContext) {
            Context applicationContext = getContext().getApplicationContext();
            if (applicationContext == null) {
                context = getContext();
            } else {
                context = new DecorContext(applicationContext, getContext());
                if (mTheme != -1) {
                    context.setTheme(mTheme);
                }
            }
        } else {
            context = getContext();
        }
        return new DecorView(context, featureId, this, getAttributes());
    }
复制代码

继续看generateLayout(mDecor)：

// Apply data from current theme.
        TypedArray a = getWindowStyle();
        ...
        // 这里下面一堆代码是 根据主题，获取DecorView的布局资源
        int layoutResource;
        int features = getLocalFeatures();
        if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
            layoutResource = R.layout.screen_swipe_dismiss;
            setCloseOnSwipeEnabled(true);
        } else if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) 
        ...
        //把布局给到mDecor，这样mDecor就有视图了。
        mDecor.onResourceLoaded(mLayoutInflater, layoutResource)
    //findViewById就是getDecorView().findViewById(id);
    //所以从DecorView中找到id为ID_ANDROID_CONTENT = com.android.internal.R.id.content 的容器，就用用来存放我们activity中设置的视图的。
    ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
    ...
    return contentParent;
}
复制代码

好了，通过以上流程，就清楚了activity中通过setContentView设置的布局实际是加载到DecorView的id为com.android.internal.R.id.content容器中。我们查看DecorView所有的主题的布局，发现都有这个id的容器，且是FrameLayout。

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:fitsSystemWindows="true">
    <!-- Popout bar for action modes -->
    <ViewStub android:id="@+id/action_mode_bar_stub"
              android:inflatedId="@+id/action_mode_bar"
              android:layout="@layout/action_mode_bar"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:theme="?attr/actionBarTheme" />

    <FrameLayout android:id="@android:id/title_container" 
        android:layout_width="match_parent" 
        android:layout_height="?android:attr/windowTitleSize"
        android:transitionName="android:title"
        style="?android:attr/windowTitleBackgroundStyle">
    </FrameLayout>
    //这个容器
    <FrameLayout android:id="@android:id/content"
        android:layout_width="match_parent" 
        android:layout_height="0dip"
        android:layout_weight="1"
        android:foregroundGravity="fill_horizontal|top"
        android:foreground="?android:attr/windowContentOverlay" />
</LinearLayout>
复制代码

最后一步，就是windowManager.addView了，在哪呢？在ActivityThred的handleResumeActivity()中:

r.activity.makeVisible();
复制代码

再看activity.makeVisible()：

void makeVisible() {
        if (!mWindowAdded) {
            ViewManager wm = getWindowManager();
            //1、windowManager.addView
            wm.addView(mDecor, getWindow().getAttributes());
            mWindowAdded = true;
        }
        //2、Decor可见
        mDecor.setVisibility(View.VISIBLE);
    }
复制代码

好了，activity的window加载过程就这样了。

3.2 Dialog的window创建

先看Dialog的构造方法:

Dialog(@NonNull Context context, @StyleRes int themeResId, boolean createContextThemeWrapper) {
        ...
        //获取windowManager
        mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        //实例化PhoneWindow
        final Window w = new PhoneWindow(mContext);
        mWindow = w;
        //设置回调
        w.setCallback(this);
        w.setOnWindowDismissedCallback(this);
        w.setOnWindowSwipeDismissedCallback(() -> {
            if (mCancelable) {
                cancel();
            }
        });
        w.setWindowManager(mWindowManager, null, null);
        ...
    }
复制代码

接着看setContentView，和activity类似，把内容视图放入DecorView：

public void setContentView(@LayoutRes int layoutResID) {
        mWindow.setContentView(layoutResID);
    }
复制代码

再看下show方法：

public void show() {
        ...
        mDecor = mWindow.getDecorView();
        ...
        WindowManager.LayoutParams l = mWindow.getAttributes();
        boolean restoreSoftInputMode = false;
        if ((l.softInputMode
                & WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION) == 0) {
            l.softInputMode |=
                    WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;
            restoreSoftInputMode = true;
        }
        //使用WindowManager.addView
        mWindowManager.addView(mDecor, l);
        ...
    }
复制代码

注意，一般创建dialog时传入的context必须是Activity。如果要传Application，那么要dialog.getWindow().setType()，设置系统window的type。

3.3 Toast的window创建

使用Toast方式：

Toast.makeText(this, "hehe", Toast.LENGTH_SHORT).show();
复制代码

看makeText()，就是new一个Toast，设置mNextView为TextView、mDuration：

public static Toast makeText(Context context, CharSequence text, @Duration int duration) {
        return makeText(context, null, text, duration);
    }
复制代码

public static Toast makeText(@NonNull Context context, @Nullable Looper looper,
            @NonNull CharSequence text, @Duration int duration) {
         //实例化
        Toast result = new Toast(context, looper);

        LayoutInflater inflate = (LayoutInflater)
                context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View v = inflate.inflate(com.android.internal.R.layout.transient_notification, null);
        TextView tv = (TextView)v.findViewById(com.android.internal.R.id.message);
        tv.setText(text);
        //设置视图、时间
        result.mNextView = v;
        result.mDuration = duration;

        return result;
    }
复制代码

Toast构造方法:

public Toast(@NonNull Context context, @Nullable Looper looper) {
        mContext = context;
        //有个TN，是个Binder对象
        mTN = new TN(context.getPackageName(), looper);
        mTN.mY = context.getResources().getDimensionPixelSize(
                com.android.internal.R.dimen.toast_y_offset);
        mTN.mGravity = context.getResources().getInteger(
                com.android.internal.R.integer.config_toastDefaultGravity);
    }
复制代码

实际也可以用setView（）自定义视图：

public void setView(View view) {
        mNextView = view;
    }
复制代码

再看show():

public void show() {
        //没有视图不行
        if (mNextView == null) {
            throw new RuntimeException("setView must have been called");
        }

        INotificationManager service = getService();
        String pkg = mContext.getOpPackageName();
        TN tn = mTN;
        tn.mNextView = mNextView;

        try {
            //IPC过程：NotificationManagerServcice.enqueueToast(),为啥要IPC过程呢？（注意这里的tn就是Toast构造方法里的new的TN）
            service.enqueueToast(pkg, tn, mDuration);
        } catch (RemoteException e) {
            // Empty
        }
    }
复制代码

看下NotificationManagerServcice.enqueueToast()：

//创建ToastRecord，callback就是传进来的TN
record = new ToastRecord(callingPid, pkg, callback, duration, token);
                        mToastQueue.add(record);
...
if (index == 0) {
  //这里看起来是show方法
     showNextToastLocked();
 }
复制代码

看不showNextToastLocked()：

void showNextToastLocked() {
        //取出第一个record，这里为啥第0个？
        ToastRecord record = mToastQueue.get(0);
        while (record != null) {
            if (DBG) Slog.d(TAG, "Show pkg=" + record.pkg + " callback=" + record.callback);
            try {
                //这里跑到TN的show方法了，显然是系统服务NotificationManagerServcice向我们的APP发起IPC过程，完成最终的show。这个保留疑问后面再看~
                record.callback.show(record.token);
                //这个就是 定时 调TN的hide方法，时间就是我们的toast的设置的show时间？为啥这么说，往下看~
                scheduleDurationReachedLocked(record);
                return;
            } 
            ...
        }
    }
复制代码

看下scheduleDurationReachedLocked(record)：

private void scheduleDurationReachedLocked(ToastRecord r)
    {
        mHandler.removeCallbacksAndMessages(r);
        Message m = Message.obtain(mHandler, MESSAGE_DURATION_REACHED, r);
        long delay = r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY;
        //handler发送定时任务MESSAGE_DURATION_REACHED，看名字就是隐藏toast，时间就是我们的long或者short
        mHandler.sendMessageDelayed(m, delay);
    }
复制代码

这个mHandler就是NMS中的handler，找到上面任务的处理方法：

private void handleDurationReached(ToastRecord record)
    {
        synchronized (mToastQueue) {
            int index = indexOfToastLocked(record.pkg, record.callback);
            if (index >= 0) {
                cancelToastLocked(index);
            }
        }
    }
复制代码

接着看：

void cancelToastLocked(int index) {
        ToastRecord record = mToastQueue.get(index);
        try {
            //果然，是TN的hide方法，哈哈
            record.callback.hide();
        } catch (RemoteException e) 
        ...
        ToastRecord lastToast = mToastQueue.remove(index);
        if (mToastQueue.size() > 0) {
            // 开始下一个~~~
            showNextToastLocked();
        }
    }
复制代码

总结下NotificationManagerServcice.enqueueToast（）这个IPC的作用：使用NMS中的mHandler 处理队列中的ToastRecord，具体就是通过IPC调用Toast中的TN的show()，然后在定时调用TN的hide（）。就是说，系统来保证toast的循序排队，及展示时间。另外还一点， 对非系统应用，队列中最多同时又50个ToastRecord：

// limit the number of outstanding notificationrecords an app can have
               //MAX_PACKAGE_NOTIFICATIONS = 50
                int count = getNotificationCountLocked(pkg, userId, id, tag);
                if (count >= MAX_PACKAGE_NOTIFICATIONS) {
                    mUsageStats.registerOverCountQuota(pkg);
                    Slog.e(TAG, "Package has already posted or enqueued " + count
                            + " notifications.  Not showing more.  package=" + pkg);
                    return false;
                }
复制代码

好了，系统进程看完了。接着看实例化Toast时的创建的TN，我们在上面分析，猜测这里才是我们想要的WIndow的创建过程，那么往下看吧：

private static class TN extends ITransientNotification.Stub {
        private final WindowManager.LayoutParams mParams = new WindowManager.LayoutParams();

        private static final int SHOW = 0;
        private static final int HIDE = 1;
        private static final int CANCEL = 2;
        final Handler mHandler;
        ...

        static final long SHORT_DURATION_TIMEOUT = 4000;
        static final long LONG_DURATION_TIMEOUT = 7000;

        TN(String packageName, @Nullable Looper looper) {
            final WindowManager.LayoutParams params = mParams;
            ...
            //window的type：TYPE_TOAST = FIRST_SYSTEM_WINDOW+5，是个系统window
            params.type = WindowManager.LayoutParams.TYPE_TOAST;
            params.setTitle("Toast");
            //window的flags
            params.flags = WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON
                    | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
                    | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;

            mPackageName = packageName;

            //这里可知，必须在有looper的线程才能new Toast，为啥呢？因为前面分析NMS中调用TN的show、Hide，因为是IPC过程，实际在App这边执行是在Bind线程池中进行的，所以需要切换到当前发Toast的线程
            if (looper == null) {
                // Use Looper.myLooper() if looper is not specified.
                looper = Looper.myLooper();
                if (looper == null) {
                    throw new RuntimeException(
                            "Can't toast on a thread that has not called Looper.prepare()");
                }
            }
            mHandler = new Handler(looper, null) {
                @Override
                public void handleMessage(Message msg) {
                    switch (msg.what) {
                        case SHOW: {
                            IBinder token = (IBinder) msg.obj;
                            handleShow(token);
                            break;
                        }
                        case HIDE: {
                            handleHide();
                            // Don't do this in handleHide() because it is also invoked by
                            // handleShow()
                            mNextView = null;
                            break;
                        }
                        case CANCEL: {
                            handleHide();
                            // Don't do this in handleHide() because it is also invoked by
                            // handleShow()
                            mNextView = null;
                            try {
                                getService().cancelToast(mPackageName, TN.this);
                            } catch (RemoteException e) {
                            }
                            break;
                        }
                    }
                }
            };
        }

        /**
         * schedule handleShow into the right thread
         */
        @Override
        public void show(IBinder windowToken) {
            if (localLOGV) Log.v(TAG, "SHOW: " + this);
            mHandler.obtainMessage(SHOW, windowToken).sendToTarget();
        }

        /**
         * schedule handleHide into the right thread
         */
        @Override
        public void hide() {
            if (localLOGV) Log.v(TAG, "HIDE: " + this);
            mHandler.obtainMessage(HIDE).sendToTarget();
        }

        public void cancel() {
            if (localLOGV) Log.v(TAG, "CANCEL: " + this);
            mHandler.obtainMessage(CANCEL).sendToTarget();
        }

        public void handleShow(IBinder windowToken) {
            ...
            if (mView != mNextView) {
                // remove the old view if necessary
                handleHide();
                //mNextView赋值给mView
                mView = mNextView;
                ...
                //1.获取WindowManager
                mWM = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);
                // the layout direction
                final Configuration config = mView.getContext().getResources().getConfiguration();
                final int gravity = Gravity.getAbsoluteGravity(mGravity, config.getLayoutDirection());
                ...
                ...
                try {
                    //2.windowManager的addView
                    mWM.addView(mView, mParams);
                    trySendAccessibilityEvent();
                } catch (WindowManager.BadTokenException e) {
                    /* ignore */
                }
            }
        }

        public void handleHide() {
            if (localLOGV) Log.v(TAG, "HANDLE HIDE: " + this + " mView=" + mView);
            if (mView != null) {
                if (mView.getParent() != null) {
                    if (localLOGV) Log.v(TAG, "REMOVE! " + mView + " in " + this);
                    //windowManager的removeView
                    mWM.removeViewImmediate(mView);
                }
            ...
                mView = null;
            }
        }
    }

所以，TN才是Toast中真正处理Window创建的地方。

好了，Window讲完啦！

参考：初步理解 Window 体系Window, WindowManager和WindowManagerService之间的关系

好了，今天就到这里，欢迎留言讨论~

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