一、前言

Window的删除过程，本文中从WindowManagerImpl开始讲起，主要做了四个事情如图右所示。

WMS删除窗口.png

二、源码分析

1、删除窗口视图

public final class ActivityThread extends ClientTransactionHandler {
    @Override
    public void handleDestroyActivity(IBinder token, boolean finishing, int configChanges,
            boolean getNonConfigInstance, String reason) {
        //最终执行Activity的onDestroy()
        ActivityClientRecord r = performDestroyActivity(token, finishing,
                configChanges, getNonConfigInstance, reason);
        if (r != null) {
            cleanUpPendingRemoveWindows(r, finishing);
            WindowManager wm = r.activity.getWindowManager();
            View v = r.activity.mDecor;
            if (v != null) {
                if (r.activity.mVisibleFromServer) {
                    mNumVisibleActivities--;
                }
                IBinder wtoken = v.getWindowToken();
                if (r.activity.mWindowAdded) {
                    if (r.mPreserveWindow) {
                        r.mPendingRemoveWindow = r.window;
                        r.mPendingRemoveWindowManager = wm;
                        r.window.clearContentView();
                    } else {
                        //进入WindowManagerImpl进行移除相关操作
                        wm.removeViewImmediate(v);
                    }
                }
                if (wtoken != null && r.mPendingRemoveWindow == null) {
                    WindowManagerGlobal.getInstance().closeAll(wtoken,
                            r.activity.getClass().getName(), "Activity");
                } else if (r.mPendingRemoveWindow != null) {
                    WindowManagerGlobal.getInstance().closeAllExceptView(token, v,
                            r.activity.getClass().getName(), "Activity");
                }
                r.activity.mDecor = null;
            }
            if (r.mPendingRemoveWindow == null) {

                WindowManagerGlobal.getInstance().closeAll(token,
                        r.activity.getClass().getName(), "Activity");
            }

            Context c = r.activity.getBaseContext();
            if (c instanceof ContextImpl) {
                ((ContextImpl) c).scheduleFinalCleanup(
                        r.activity.getClass().getName(), "Activity");
            }
        }
        if (finishing) {
            try {
                ActivityTaskManager.getService().activityDestroyed(token);
            } catch (RemoteException ex) {
                throw ex.rethrowFromSystemServer();
            }
        }
        mSomeActivitiesChanged = true;
    }
}

进入WindowManagerImpl，因为WindowManager继承ViewManager，所以WindowManagerImpl 才有相关的添加，删除和更新操作。

public final class WindowManagerImpl implements WindowManager {
    @Override
    public void removeView(View view) {
        mGlobal.removeView(view, false);
    }

    //立即移除
    @Override
    public void removeViewImmediate(View view) {
        mGlobal.removeView(view, true);
    }
}

进入WindowManagerGlobal

public final class WindowManagerGlobal {
    //要销毁试图集合，存放的是DecorView 
    private final ArraySet<View> mDyingViews = new ArraySet<View>();

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

        synchronized (mLock) {
            //获取 View 在集合中的位置
            int index = findViewLocked(view, true);
            //获取ViewRootImpl中的DecorView 
            View curView = mRoots.get(index).getView();
            removeViewLocked(index, immediate);
            if (curView == view) { //删除的是DecorView 直接返回，否则抛出异常
                return;
            }

            throw new IllegalStateException("Calling with view " + view
                    + " but the ViewAncestor is attached to " + curView);
        }
    }

    //获取删除View在mView集合中的索引
    private int findViewLocked(View view, boolean required) {
        final int index = mViews.indexOf(view);
        if (required && index < 0) {
            throw new IllegalArgumentException("View=" + view + " not attached to window manager");
        }
        return index;
    }

    private void removeViewLocked(int index, boolean immediate) {
        ViewRootImpl root = mRoots.get(index);
        View view = root.getView();//DecorView 

        if (view != null) {
            InputMethodManager imm = InputMethodManager.getInstance();
            if (imm != null) {
                imm.windowDismissed(mViews.get(index).getWindowToken());
            }
        }
        boolean deferred = root.die(immediate);
        if (view != null) {
            view.assignParent(null);
            if (deferred) {
                //添加到移除试图集合中
                mDyingViews.add(view);
            }
        }
    }
}

2、判断是否立即执行删除

在ViewRootImpl中die方法中，会先判断是否立即执行删除，如果被判处死刑且立即执行则调用doDie方法，如果不是则通过Handler方法执行死刑的信号，判个缓刑。

boolean die(boolean immediate) {.
    //immediate 是否立即执行 为ture则立即执行删除
    if (immediate && !mIsInTraversal) {
        doDie();
        return false;
    }
    ......
 
    //通过Handler发送死亡信息，判处死缓
    //最终执行到 doDie() 方法
    mHandler.sendEmptyMessage(MSG_DIE);
    return true;
}

void doDie() {
    //检查线程
    checkThread();
    if (LOCAL_LOGV) Log.v(mTag, "DIE in " + this + " of " + mSurface);
    synchronized (this) {
        //判断是否删除
        if (mRemoved) {
            return;
        }
        //防止重复调用
        mRemoved = true;
        if (mAdded) {
            //做数据清除 注销操作，调用session的remove方法
            dispatchDetachedFromWindow();
        }

        if (mAdded && !mFirst) {
            destroyHardwareRenderer();

            if (mView != null) {
                int viewVisibility = mView.getVisibility();
                boolean viewVisibilityChanged = mViewVisibility != viewVisibility;
                if (mWindowAttributesChanged || viewVisibilityChanged) {
                    try {
                        if ((relayoutWindow(mWindowAttributes, viewVisibility, false)
                                & WindowManagerGlobal.RELAYOUT_RES_FIRST_TIME) != 0) {
                            mWindowSession.finishDrawing(
                                    mWindow, null /* postDrawTransaction */);
                        }
                    } catch (RemoteException e) {
                    }
                }
                //销毁画布
                destroySurface();
            }
        }

        mAdded = false;
    }
    //调用WindowManagerGlobal移除方法
    WindowManagerGlobal.getInstance().doRemoveView(this);
}

ViewRootImpl@checkThread() 检查线程的正确性

void checkThread() {
        if (mThread != Thread.currentThread()) {
            throw new CalledFromWrongThreadException(
                    "Only the original thread that created a view hierarchy can touch its views.");
        }
    }

在ViewRootImpl的dispatchDetachedFromWindow方法中会调用 Session 与WMS进行通信，然后执行移除的操作。

    void dispatchDetachedFromWindow() {
        mFirstInputStage.onDetachedFromWindow();
        if (mView != null && mView.mAttachInfo != null) {
            mAttachInfo.mTreeObserver.dispatchOnWindowAttachedChange(false);
            mView.dispatchDetachedFromWindow();
        }

        mAccessibilityInteractionConnectionManager.ensureNoConnection();
        mAccessibilityManager.removeAccessibilityStateChangeListener(
                mAccessibilityInteractionConnectionManager);
        mAccessibilityManager.removeHighTextContrastStateChangeListener(
                mHighContrastTextManager);
        removeSendWindowContentChangedCallback();

        destroyHardwareRenderer(); //删除硬件渲染

        setAccessibilityFocus(null, null);

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

        mSurface.release(); //销毁Surface.

        if (mInputQueueCallback != null && mInputQueue != null) {
            mInputQueueCallback.onInputQueueDestroyed(mInputQueue);
            mInputQueue.dispose();
            mInputQueueCallback = null;
            mInputQueue = null;
        }
        if (mInputEventReceiver != null) {
            mInputEventReceiver.dispose();
            mInputEventReceiver = null;
        }
        try {// 通过IWindowSession 关联到 WMS中删除信息
            mWindowSession.remove(mWindow);
        } catch (RemoteException e) {
        }

   
        if (mInputChannel != null) {
            mInputChannel.dispose();
            mInputChannel = null;
        }

        mDisplayManager.unregisterDisplayListener(mDisplayListener);

        unscheduleTraversals();
    }

在WMS的removeWindow 函数中，先会通过Session和Client获取到当前窗口在WMS的副本也就是WindowState，如果不为空则执行删除操作。

会进入 Session@remove 方法，Session 时 IWindowSession的实现类

class Session extends IWindowSession.Stub implements IBinder.DeathRecipient {
    final WindowManagerService mService;

    @Override
    public void remove(IWindow window) {
        mService.removeWindow(this, window);
    }
}

进入到WindowManagerService@removeWindow 方法

//每个WMS都有一个唯一的 Session
void removeWindow(Session session, IWindow client) {
    synchronized (mGlobalLock) {
        //获取WindowState
        WindowState win = windowForClientLocked(session, client, false);
        if (win != null) {
            //执行删除
            win.removeIfPossible();
            return;
        }
        mEmbeddedWindowController.remove(client);
    }
}

从WMS中获取WindowState

    final HashMap<IBinder, WindowState> mWindowMap = new HashMap<>();

    final WindowState windowForClientLocked(Session session, IWindow client, boolean throwOnError) {
        return windowForClientLocked(session, client.asBinder(), throwOnError);
    }

    final WindowState windowForClientLocked(Session session, IBinder client, boolean throwOnError) {
        WindowState win = mWindowMap.get(client);
        if (DEBUG) Slog.v(TAG_WM, "Looking up client " + client + ": " + win);
        if (win == null) {
            if (throwOnError) {
                throw new IllegalArgumentException(
                        "Requested window " + client + " does not exist");
            }
            ProtoLog.w(WM_ERROR, "Failed looking up window session=%s callers=%s", session,
                    Debug.getCallers(3));
            return null;
        }
        if (session != null && win.mSession != session) {
            if (throwOnError) {
                throw new IllegalArgumentException("Requested window " + client + " is in session "
                        + win.mSession + ", not " + session);
            }
            ProtoLog.w(WM_ERROR, "Failed looking up window session=%s callers=%s", session,
                    Debug.getCallers(3));
            return null;
        }

        return win;
    }

重置和删除WindowState状态
win.removeIfPossible 方法和它的名字一样，并不是直接执行删除操作，而是进行多个条件判断过滤，满足其中一个条件就会return，推迟删除操作。比如View正在运行一个动画，这是就会推迟删除操作知道动画完成。然后调用 removeImmediately 方法。

class WindowState extends WindowContainer<WindowState> implements WindowManagerPolicy.WindowState,
        InsetsControlTarget {
    void removeImmediately() {
    super.removeImmediately();
    //已经删除
    if (mRemoved) {
        // Nothing to do.
        ProtoLog.v(WM_DEBUG_ADD_REMOVE,
                "WS.removeImmediately: %s Already removed...", this);
        return;
    }
    //移除标记
    mRemoved = true;
    ......

    final DisplayContent dc = getDisplayContent();
    ......
    //policy做移除操作
    dc.getDisplayPolicy().removeWindowLw(this);
    //关闭输入事件渠道
    disposeInputChannel();
    
    mWinAnimator.destroyDeferredSurfaceLocked();
    mWinAnimator.destroySurfaceLocked();
    //Session集合冲移除WindowState
    mSession.windowRemovedLocked();
    .....
    //集中处理清除工作
    mWmService.postWindowRemoveCleanupLocked(this);
    }   
}

3、WindowManagerGlobal 相关数据删除

在WindowManagerGlobal方法中，会删除相关的一些数据，如ViewRootImpl、LayoutParams、DecorView，并将DecorView加入到死亡列表中。

WindowManagerGlobal@doRemoveView(...)

void doRemoveView(ViewRootImpl root) {
      boolean allViewsRemoved;
        synchronized (mLock) {
            //从ViewRootImpl获取到索引值
            final int index = mRoots.indexOf(root);
            if (index >= 0) {
                //删除ViewRootImpl列表中的数据
                mRoots.remove(index);
                //删除LayoutParams列表中的数据
                mParams.remove(index);
                //删除DecorView列表中的数据
                final View view = mViews.remove(index);
                //DecorView加入到死亡列表
                mDyingViews.remove(view);
            }
            allViewsRemoved = mRoots.isEmpty();
        }
      if (ThreadedRenderer.sTrimForeground && ThreadedRenderer.isAvailable()) {
          doTrimForeground();
        }
      if (allViewsRemoved) {
          InsetsAnimationThread.release();
      }
}

WMS(三)-删除Window