android7.0 multiWindow 之拖拽失效(android事件分發機制分析)

前言：讓生活每天都充滿憧憬，而不是日復一日的重複，學會用孩子的眼光看待這個世界。

效果圖

現象：
下拉中間的白色的按鈕沒有反應。正常情況下下拉是可以的。
這個控件的觸摸事件沒有反應。通過對系統app SystemUI的學習，瞭解到這個控件叫做DividerView，屬於多窗口模式下的一個分割兩個Activity的view組件
code在

Z:\frameworks\base\packages\SystemUI\src\com\android\systemui\stackdivider

從佈局文件

<com.android.systemui.stackdivider.DividerView
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_height="match_parent"
        android:layout_width="match_parent">

    <View
        style="@style/DockedDividerBackground"
        android:id="@+id/docked_divider_background"
        android:background="@color/docked_divider_background"/>

    <com.android.systemui.stackdivider.MinimizedDockShadow
        style="@style/DockedDividerMinimizedShadow"
        android:id="@+id/minimized_dock_shadow"
        android:alpha="0"/>">

    <com.android.systemui.stackdivider.DividerHandleView
        style="@style/DockedDividerHandle"
        android:id="@+id/docked_divider_handle"
        android:contentDescription="@string/accessibility_divider"
        android:background="@null"/>

</com.android.systemui.stackdivider.DividerView>

得出這DividerView（分割線的黑色部分）、DividerHandleView(f分割線的白色部分)一個相當於ViewGroup(onTouchEvent、dispatchTouchEvent、onInterceptTouchEvent)，一個是View（onTouchEvent、dispatchTouchEvent）。

看一下code

/**
 * View for the handle in the docked stack divider.
 */
public class DividerHandleView extends View{
...
  @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        Log.d("elliotlog","DividerHandleView onTouchEvent");
        return super.onTouchEvent(event);
    }
@Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        Log.d("elliotlog","DividerHandleView dispatchTouchEvent");
        return super.dispatchTouchEvent(event);
    }
...
}

public class DividerView extends FrameLayout implements OnTouchListener{
...

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        Log.d("elliotlog","DividerView onTouchEvent");
        return onTouch(mHandle,event);

    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        // TODO Auto-generated method stub
        Log.d("elliotlog","DividerView onInterceptTouchEvent");
        return super.onInterceptTouchEvent(ev);
    }
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        // TODO Auto-generated method stub
        Log.d("elliotlog","DividerView dispatchTouchEvent");
        boolean flag=super.dispatchTouchEvent(ev);
        if(flag){Log.d("elliotlog","is DividerView dispatchTouchEvent");}else{Log.d("elliotlog","not DividerView dispatchTouchEvent");}
        return flag;
    }
//拖拽效果實現會調用的方法
  public boolean onTouch(View v, MotionEvent event) {
    Log.d("elliotlog","onTouch");
        convertToScreenCoordinates(event);
        mGestureDetector.onTouchEvent(event);
        final int action = event.getAction() & MotionEvent.ACTION_MASK
        switch (action) {
            case MotionEvent.ACTION_DOWN:
        Log.d("elliotlog","MotionEvent.ACTION_DOWN:"+MotionEvent.ACTION_DOWN);
                mVelocityTracker = VelocityTracker.obtain();
                mVelocityTracker.addMovement(event);
                mStartX = (int) event.getX();
                mStartY = (int) event.getY();
                boolean result = startDragging(true /* animate */, true /* touching */);
                if (!result) {

                    // Weren't able to start dragging successfully, so cancel it again.
                    stopDragging();
                }
                mStartPosition = getCurrentPosition();
                mMoving = false;
                return result;
            case MotionEvent.ACTION_MOVE:
        Log.d("elliotlog","MotionEvent.ACTION_MOVE:"+MotionEvent.ACTION_MOVE);
                mVelocityTracker.addMovement(event);
                int x = (int) event.getX();
                int y = (int) event.getY();
                boolean exceededTouchSlop =
                        isHorizontalDivision() && Math.abs(y - mStartY) > mTouchSlop
                                || (!isHorizontalDivision() && Math.abs(x - mStartX) > mTouchSlop);
                if (!mMoving && exceededTouchSlop) {
                    mStartX = x;
                    mStartY = y;
                    mMoving = true;
                }
                if (mMoving && mDockSide != WindowManager.DOCKED_INVALID) {
                    SnapTarget snapTarget = mSnapAlgorithm.calculateSnapTarget(
                            mStartPosition, 0 /* velocity */, false /* hardDismiss */);
                    resizeStack(calculatePosition(x, y), mStartPosition, snapTarget);
                }
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
        Log.d("elliotlog","MotionEvent.ACTION_UP:"+MotionEvent.ACTION_UP);
                mVelocityTracker.addMovement(event);

                x = (int) event.getRawX();
                y = (int) event.getRawY();

                mVelocityTracker.computeCurrentVelocity(1000);
                int position = calculatePosition(x, y);
                stopDragging(position, isHorizontalDivision() ? mVelocityTracker.getYVelocity()
                        : mVelocityTracker.getXVelocity(), false /* avoidDismissStart */,
                        true /* log */);
                mMoving = false;
                break;
        }
        return true;
    }
...
}

點擊DividerHandleView，並且嘗試向下滑動。log打印如下

03-02 04:38:33.973 D/elliotlog( 1403): DividerView dispatchTouchEvent
03-02 04:38:33.973 D/elliotlog( 1403): DividerView onTouchEvent
03-02 04:38:33.973 D/elliotlog( 1403): not DividerView dispatchTouchEvent
03-02 04:38:35.030 D/elliotlog( 1403): DividerView dispatchTouchEvent
03-02 04:38:35.030 D/elliotlog( 1403): DividerView onTouchEvent
03-02 04:38:35.030 D/elliotlog( 1403): not DividerView dispatchTouchEvent

會發現連onInterceptTouchEvent事件都沒有執行。而是DividerView分發了之後就直接自己消費掉了onTouchEvent。

這顯然不符合我們正常的邏輯，當我們不復現這個bug時，會發現打印的很正常

03-02 06:00:31.919 D/elliotlog( 1397): DividerView dispatchTouchEvent
03-02 06:00:31.919 D/elliotlog( 1397): DividerView onInterceptTouchEvent
03-02 06:00:31.919 D/elliotlog( 1397): DividerHandleView dispatchTouchEvent
03-02 06:00:31.920 D/elliotlog( 1397): onTouch
03-02 06:00:31.920 D/elliotlog( 1397): MotionEvent.ACTION_DOWN:0
03-02 06:00:31.922 D/elliotlog( 1397): is DividerView dispatchTouchEvent
03-02 06:00:32.045 D/elliotlog( 1397): DividerView dispatchTouchEvent
03-02 06:00:32.045 D/elliotlog( 1397): DividerView onInterceptTouchEvent
03-02 06:00:32.045 D/elliotlog( 1397): DividerHandleView dispatchTouchEvent
03-02 06:00:32.045 D/elliotlog( 1397): onTouch
03-02 06:00:32.046 D/elliotlog( 1397): MotionEvent.ACTION_MOVE:2

首先是DividerView dispatchTouchEvent，然後內部會調用onInterceptTouchEvent，於是子View DividerHandleView會分發dispatchTouchEvent，view是沒有onInterceptTouchEvent，即不會攔截 ，內部會調用 OnTouchListener的onTouch，上面貼的代碼中這個方法返回了ture。消費了，所以子view的onTouchEvent方法不會執行了。

回到原點，我們還是要分析錯誤的情況。
我們發現，在Divider.java中存在這樣的一個監聽接口，

  class DockDividerVisibilityListener extends IDockedStackListener.Stub {
...
  @Override
        public void onAdjustedForImeChanged(boolean adjustedForIme, long animDuration)
                throws RemoteException {
            mView.post(() -> {
                if (mAdjustedForIme != adjustedForIme) {
                    mAdjustedForIme = adjustedForIme;
                    updateTouchable();
                    if (!mMinimized) {
                        if (animDuration > 0) {
                            mView.setAdjustedForIme(adjustedForIme, animDuration);
                        } else {
                            mView.setAdjustedForIme(adjustedForIme);
                        }
                    }
                }
            });
        }
...
}

  private void updateTouchable() {
        mWindowManager.setTouchable(!mMinimized && !mAdjustedForIme);
    }

也就說當Divider最小化，或者需要調整（如出現輸入法時）會設爲不可觸摸（由framework層控制），這就出現了剛纔的分發機制不符合規矩的做法，從而出現這個bug。

着個監聽器是如何註冊的
在Divider.java（SystemUI）

 SystemServicesProxy ssp = Recents.getSystemServices();
        ssp.registerDockedStackListener(mDockDividerVisibilityListener);

在SystemServicesProxy.java中（SystemUI）

public void registerDockedStackListener(IDockedStackListener listener) {
        if (mWm == null) return;

        try {
            WindowManagerGlobal.getWindowManagerService().registerDockedStackListener(listener);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

在WindowManagerService.java(framework)

@Override
    public void registerDockedStackListener(IDockedStackListener listener) {
        if (!checkCallingPermission(android.Manifest.permission.REGISTER_WINDOW_MANAGER_LISTENERS,
                "registerDockedStackListener()")) {
            return;
        }
        // TODO(multi-display): The listener is registered on the default display only.
        getDefaultDisplayContentLocked().mDividerControllerLocked.registerDockedStackListener(
                listener);
    }

在DockedStackDividerController.java

  void registerDockedStackListener(IDockedStackListener listener) {
        mDockedStackListeners.register(listener);
        notifyDockedDividerVisibilityChanged(wasVisible());
        notifyDockedStackExistsChanged(
                mDisplayContent.mService.mStackIdToStack.get(DOCKED_STACK_ID) != null);
        notifyDockedStackMinimizedChanged(mMinimizedDock, 0 /* animDuration */);
        notifyAdjustedForImeChanged(mAdjustedForIme, 0 /* animDuration */);

    }

notifyAdjustedForImeChanged

 void notifyAdjustedForImeChanged(boolean adjustedForIme, long animDuration) {
        final int size = mDockedStackListeners.beginBroadcast();
        for (int i = 0; i < size; ++i) {
            final IDockedStackListener listener = mDockedStackListeners.getBroadcastItem(i);
            try {
                listener.onAdjustedForImeChanged(adjustedForIme, animDuration);
            } catch (RemoteException e) {
                Slog.e(TAG_WM, "Error delivering adjusted for ime changed event.", e);
            }
        }
        mDock

這裏面完成了註冊