Window和WindowManager--《Android開發藝術探索》閱讀筆記——第八章

Window，表示一個窗口的抽象的概念；同時也是一個抽象類，唯一的實現是PhoneWindow。在PhoneWindow中有一個頂級View—DecorView，繼承自FrameLayout，我們可以通過getDecorView()獲得它，當我們調用Activity的setContentView時，其實最終會調用Window的setContentView，當我們調用Activity的findViewById時，其實最終調用的是Window的findViewById，這也間接的說明了Window是View的直接管理者。
但是Window並不是真實存在的，它更多的表示一種抽象的功能集合，View纔是Android中的視圖呈現形式，繪製到屏幕上的是View不是Window，但是View不能單獨存在，它必需依附在Window這個抽象的概念上面，Android中需要依賴Window提供視圖的有Activity，Dialog，Toast，PopupWindow，StatusBarWindow（系統狀態欄），輸入法窗口等，因此Activity，Dialog等視圖都對應着一個Window。

創建Window，通過WindowManager即可完成。WindowManager是操作Window的入口，Window的具體實現是在WindowManagerService中。WindowManager和WindowManagerService交互是IPC（跨進程通信）過程。

Window是View的管理者，當我們說創建Window時，一方面指實例化這個管理者，一方面指 用WindowManager.addView()添加view，以view的形式來呈現Window這個概念。

一、Window和WindowManager

1.1 window

先看創建window的代碼

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);

實際就只有一句windowManager.addView(view, layoutParams)，這樣就添加了一個Window，這個window只有一個button。看下LayoutParams的兩個不太認識的屬性，flags、type。
flags，決定window的顯示特性，有很多值，看下常用的：
FLAG_NOT_FOCUSABLE，不需要獲取焦點、不需要 輸入事件，同時會自定開啓FLAG_NOT_TOUCH_MODAL，最終事件會傳遞給下層具有焦點的window。
FLAG_NOT_TOUCH_MODAL，window區域以外的單擊事件會傳遞給下層window，window範圍內的事件自己處理。一般需要開啓此標記，否則其他window不能收到事件。
FLAG_SHOW_WHEN_LOCKED，開啓後 可以讓window顯示在鎖屏的界面上。

type參數表示window的類型。window有三種類型，應用window、子window、系統window。應用window對應activity；子window要依附在父window上，如dialog；系統window需要申明權限才能創建，比如toast、系統狀態欄。
window是分層的，每個window都有對應的z-ordered，層級大的在層級小的上層。應用window的層級範圍是1-99，子window是1000-19999=，系統window是2000-2999，即type的值。

如果想window位於所有window頂層，那就用系統window。可以設置layoutParams.type = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY，並且，要申明使用權限，且6.0以後要讓用戶手動打開權限。

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/>

否則會報錯：

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) 

使用系統window的完整代碼：

    private void initCustomWindow() {
        //6.0以上需要用戶手動打開權限
        // (SYSTEM_ALERT_WINDOW and WRITE_SETTINGS, 這兩個權限比較特殊，
        // 不能通過代碼申請方式獲取，必須得用戶打開軟件設置頁手動打開，才能授權。Manifest申請該權限是無效的。)
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M){
            if (!Settings.canDrawOverlays(this)) {
                //打開設置頁，讓用戶打開設置
                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 {
                //已經打開了權限
                handleAddWindow();
            }
        }else {
            //6.0以下直接 Manifest申請該權限 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 設置 Window 屬性
        layoutParams.flags= WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL;
        // type 設置 Window 類別（層級）：系統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)) {
                    //打開了權限
                    handleAddWindow();
                }else {
                    Toast.makeText(this, "can not DrawOverlays", Toast.LENGTH_SHORT).show();
                }
                break;
            default:
                break;
        }
    }

按home鍵後效果：

1.2 WindowManager

WindowManager是個接口，繼承自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);
}

所以，windowManager就是 添加、更新、刪除 view，實際使用的就是這三個方法，上面創建window的例子用的就是addView方法。所以，操作window就是操作view。

二、window的內部機制

window是抽象的概念，在視圖中不是實際存在，它以view的形式呈現。一個window就對應一個view，window操作view實際是通過ViewRootImpl實現。使用中是通過WindowManager對的操作，無法直接訪問window。下面就看看WindowManager的三個方法。

2.1 window的添加

WindowManager的實現類是WindowManagerImpl，那麼看看操作view的三個方法的實現：

@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);
    }

可以看到，全都交給mGlobal處理了，那看下mGlobal，是個單例對象：

private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();

public static WindowManagerGlobal getInstance() {
        synchronized (WindowManagerGlobal.class) {
            if (sDefaultWindowManager == null) {
                sDefaultWindowManager = new WindowManagerGlobal();
            }
            return sDefaultWindowManager;
        }
    }

那麼來看下mGlobal.addView，具體簡要概括爲3個步驟：

1. 數據檢查
2. 更新各種參數列表
3. RootViewImpl添加view（含window的添加）

public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
        //1、數據檢查
        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;
        ...
        	//創建viewRoot（一個window對應一個viewRoot）
            root = new ViewRootImpl(view.getContext(), display);
            view.setLayoutParams(wparams);
			
			//2、更新各種參數列：所有window的--view的列表、rootView的列表、view參數的列表
            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;
            }
        }
    }

接着看ViewRootImpl的setView：

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
				...
				//1.繪製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.通過session與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);
                }
				...
}

兩個步驟：1、調用requestLayout()異步刷新view，2、mWindowSession.addToDisplay()完成window的添加。

requestLayout()內部最後走到performTraversals()，我們知道這是view繪製流程入口。如下所示：

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

void scheduleTraversals() {
        if (!mTraversalScheduled) {
            mTraversalScheduled = true;
            mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
            mChoreographer.postCallback(
                    Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
            if (!mUnbufferedInputDispatch) {
                scheduleConsumeBatchedInput();
            }
            notifyRendererOfFramePending();
            pokeDrawLockIfNeeded();
        }
    }

final class TraversalRunnable implements Runnable {
        @Override
        public void run() {
            doTraversal();
        }
    }

void doTraversal() {
        if (mTraversalScheduled) {
            mTraversalScheduled = false;
            mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);

            if (mProfile) {
                Debug.startMethodTracing("ViewAncestor");
            }
			// 繪製流程
            performTraversals();

            if (mProfile) {
                Debug.stopMethodTracing();
                mProfile = false;
            }
        }
    }

至於mWindowSession.addToDisplay()，先看mWindowSession，類型是IWindowSession，是個Binder對象，具體是com.android.server.wm.Session，所以window的添加是一個IPC過程。
mWindowSessionde 是在ViewRootImpl創建時獲取，由WindowManagerGlobal通過獲取WindowManagerService來爲 每個應用創建一個單獨的session。

public ViewRootImpl(Context context, Display display) {
        mContext = context;
        mWindowSession = WindowManagerGlobal.getWindowSession();
	...
}

    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;
        }
    }

    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;
        }
    }

然後是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;
    }

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);
    }

window的添加就交給WindowManagerService了。
WindowManagerService主要作用：
窗口管理： 是先進行窗口的權限檢查，因爲系統窗口需要聲明權限，然後根據相關的Display信息以及窗口信息對窗口進行校對，再然後獲取對應的WindowToken，再根據不同的窗口類型檢查窗口的有效性，如果上面一系列步驟都通過了，就會爲該窗口創建一個WindowState對象，以維護窗口的狀態和根據適當的時機調整窗口狀態，最後就會通過WindowState的attach方法與SurfaceFlinger通信。因此SurfaceFlinger能使用這些Window信息來合成surfaces,並渲染輸出到顯示設備。
輸入事件的中轉站：當我們的觸摸屏幕時就會產生輸入事件，在Android中負責管理事件的輸入是InputManagerService，它裏面有一個InputManager，在啓動IMS的同時會創建InputManager，在創建InputManager同時創建InputReader和InputDispatcher，InputReader會不斷的從設備節點中讀取輸入事件，InputReader將這些原始輸入事件加工後就交給InputDispatcher，而InputDispatcher它會尋找一個最合適的窗口來處理輸入事件，WMS是窗口的管理者，WMS會把所有窗口的信息更新到InputDispatcher中，這樣InputDispatcher就可以將輸入事件派發給合適的Window，Window就會把這個輸入事件傳給頂級View，然後就會涉及我們熟悉的事件分發機制。

2.2 window的更新

直接看mGlobal.updateViewLayout(view, params)：

    public void updateViewLayout(View view, ViewGroup.LayoutParams params) {
    	//1、參數檢查
        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及參數列表列表
        view.setLayoutParams(wparams);
        synchronized (mLock) {
            int index = findViewLocked(view, true);
            ViewRootImpl root = mRoots.get(index);
            mParams.remove(index);
            mParams.add(index, wparams);
            //3、RootViewImpl更新佈局
            root.setLayoutParams(wparams, false);
        }
    }

再看ViewRootIml.setLayoutParams()中會調用scheduleTraversals() 重新繪製佈局，其中也會調用mWindowSession.relayout來更新window ，也是IPC過程。

2.3 window 刪除

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);
        }
    }

再看removeViewLocked(index, immediate)：

    private void removeViewLocked(int index, boolean immediate) {
    	//找到對應的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來刪除
        boolean deferred = root.die(immediate);
        if (view != null) {
            view.assignParent(null);
            if (deferred) {
            	//記錄要刪除的view
                mDyingViews.add(view);
            }
        }
    }

繼續看root.die(immediate)：

    boolean die(boolean immediate) {
        // 如果是立刻刪除，直接調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());
        }
        //不是立刻刪，就放入隊列
        mHandler.sendEmptyMessage(MSG_DIE);
        return true;
    }

繼續看doeDie()：

    void doDie() {
        checkThread();
        if (LOCAL_LOGV) Log.v(mTag, "DIE in " + this + " of " + mSurface);
        synchronized (this) {
            if (mRemoved) 
                return;
            }
            mRemoved = true;
            if (mAdded) {
            	//刪除操作
                dispatchDetachedFromWindow();
            }
            
            ...
         //移除對應列表中的root、view、param、dyingView
        WindowManagerGlobal.getInstance().doRemoveView(this);
    }

看下dispatchDetachedFromWindow()：

    void dispatchDetachedFromWindow() {
        mFirstInputStage.onDetachedFromWindow();
        if (mView != null && mView.mAttachInfo != null) {
            mAttachInfo.mTreeObserver.dispatchOnWindowAttachedChange(false);
            //回調view的dispatchDetachedFromWindow方法，意思是view要從window中移除了。一般可在其中做一些資源回收工作，如 停止動畫等。
            mView.dispatchDetachedFromWindow();
        }
		//移除各種回調
        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 {
        	//刪除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();
    }

好了，window的三個view操作就這些了。

三、常見Window的創建過程

View依附於Window這個抽象概念，有Activity、Dialog、Toast、PopupWindow等。

3.1 Activity的Window創建

Activity的啓動略複雜，這裏先看ActivityThread裏的performLaunchActivity()：

    private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
    ...
    //創建activity實例：通過類加載器創建
	java.lang.ClassLoader cl = appContext.getClassLoader();
    activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);
    ...
    //調用Activity的attach方法--關聯上下文環境變量
  	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);    
	...
}

接着看activity.attach方法：

        //實例化window，就是Window的唯一實現PhoneWindow
        mWindow = new PhoneWindow(this, window, activityConfigCallback);
        ...
        //把activity作爲回調接口傳入window，這樣window從外界接受的狀態變化都會交給activity
        //例如：dispatchTouchEvent、onAttachedToWindow、onDetachedFromWindow
        mWindow.setCallback(this);
        ...
        //設置windowManager，實際就是WindowManagerImpl的實例，在activity中getWindowManager()獲取的就是這個實例
        mWindow.setWindowManager(
                (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
                mToken, mComponent.flattenToString(),
                (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
        ...
        mWindowManager = mWindow.getWindowManager();

OK，activity視圖的管理者window已創建，那麼什麼時候用windowManager.addView() 來把activity的視圖依附在window上呢？

先看Activity的setContentView方法，我們activity的視圖由此方法設置：

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

接着看PhonrWindow的setContentView：

    public void setContentView(int layoutResID) {
        // mContentParent爲空，就調installDecor()，猜想installDecor()裏面創建了mContentParent。且從名字看出mContentParent就是內容視圖的容器
        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 {
        	//這裏看到，確實把我們的視圖加載到mContentParent了
            mLayoutInflater.inflate(layoutResID, mContentParent);
        }
        ...
    }

那就看installDecor():

private void installDecor() {
	if (mDecor == null) {
			//創建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) {
        	//創建mContentParent
            mContentParent = generateLayout(mDecor);
   ...
}

看下generateDecor(-1)，就是new了個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());
    }

繼續看generateLayout(mDecor)：

		// Apply data from current theme.
        TypedArray a = getWindowStyle();
        ...
        // 這裏下面一堆代碼是 根據主題，獲取DecorView的佈局資源
        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) 
        ...
        //把佈局給到mDecor，這樣mDecor就有視圖了。
        mDecor.onResourceLoaded(mLayoutInflater, layoutResource)
	//findViewById就是getDecorView().findViewById(id);
	//所以從DecorView中找到id爲ID_ANDROID_CONTENT = com.android.internal.R.id.content 的容器，就用用來存放我們activity中設置的視圖的。
	ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
	...
    return contentParent;
}

好了，通過以上流程，就清楚了activity中通過setContentView設置的佈局實際是加載到DecorView的id爲com.android.internal.R.id.content容器中。我們查看DecorView所有的主題的佈局，發現都有這個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>
    //這個容器
    <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>

最後一步，就是windowManager.addView了，在哪呢？
在ActivityThred的handleResumeActivity()中:

r.activity.makeVisible();

再看activity.makeVisible()：

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

好了，activity的window加載過程就這樣了。

3.2 Dialog的window創建

先看Dialog的構造方法:

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

接着看setContentView，和activity類似，把內容視圖放入DecorView：

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

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);
        ...
    }

注意，一般創建dialog時 傳入的context必須是Activity。如果要傳Application，那麼要dialog.getWindow().setType()，設置系統window的type。

3.3 Toast的window創建

使用Toast方式：

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

看makeText()，就是new一個Toast，設置mNextView爲TextView、mDuration：

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

    public static Toast makeText(@NonNull Context context, @Nullable Looper looper,
            @NonNull CharSequence text, @Duration int duration) {
         //實例化
        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);
		//設置視圖、時間
        result.mNextView = v;
        result.mDuration = duration;

        return result;
    }

Toast構造方法:

    public Toast(@NonNull Context context, @Nullable Looper looper) {
        mContext = context;
        //有個TN，是個Binder對象
        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);
    }

實際也可以用setView（）自定義視圖：

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

再看show():

    public void show() {
    	//沒有視圖不行
        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過程：NotificationManagerServcice.enqueueToast(),爲啥要IPC過程呢？（注意這裏的tn就是Toast構造方法裏的new的TN）
            service.enqueueToast(pkg, tn, mDuration);
        } catch (RemoteException e) {
            // Empty
        }
    }

看下NotificationManagerServcice.enqueueToast()：

//創建ToastRecord，callback就是傳進來的TN
record = new ToastRecord(callingPid, pkg, callback, duration, token);
                        mToastQueue.add(record);
...
if (index == 0) {
	//這裏看起來是show方法
     showNextToastLocked();
 }

看不showNextToastLocked()：

    void showNextToastLocked() {
    	//取出第一個record，這裏爲啥第0個？
        ToastRecord record = mToastQueue.get(0);
        while (record != null) {
            if (DBG) Slog.d(TAG, "Show pkg=" + record.pkg + " callback=" + record.callback);
            try {
            	//這裏跑到TN的show方法了，顯然是系統服務NotificationManagerServcice向我們的APP發起IPC過程，完成最終的show。這個保留疑問後面再看~
                record.callback.show(record.token);
                //這個就是 定時 調TN的hide方法，時間就是我們的toast的設置的show時間？爲啥這麼說，往下看~
                scheduleDurationReachedLocked(record);
                return;
            } 
            ...
        }
    }

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發送定時任務MESSAGE_DURATION_REACHED，看名字就是隱藏toast，時間就是我們的long或者short
        mHandler.sendMessageDelayed(m, delay);
    }

這個mHandler就是NMS中的handler，找到上面任務的處理方法：

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

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) {
            // 開始下一個~~~
            showNextToastLocked();
        }
    }

總結下NotificationManagerServcice.enqueueToast（）這個IPC的作用：使用NMS中的mHandler 處理隊列中的ToastRecord，具體就是通過IPC調用Toast中的TN的show()，然後在定時調用TN的hide（）。就是說，系統來保證toast的循序排隊，及展示時間。
另外還一點，對非系統應用，隊列中最多同時又50個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;
                }

好了，系統進程看完了。接着看實例化Toast時的創建的TN，我們在上面分析，猜測 這裏纔是我們想要的WIndow的創建過程，那麼往下看吧：

    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，是個系統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;
			
			//這裏可知，必須在有looper的線程才能new Toast，爲啥呢？因爲前面分析NMS中調用TN的show、Hide，因爲是IPC過程，實際在App這邊執行是在Bind線程池中進行的，所以需要切換到當前發Toast的線程
            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賦值給mView
                mView = mNextView;
                ...
                //1.獲取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纔是Toast中真正處理Window創建的地方。

好了，Window講完啦！

參考：
初步理解 Window 體系
Window, WindowManager和WindowManagerService之間的關係