Android Touch イベント配信についての深い理解

public boolean dispatchTouchEvent(MotionEvent ev) {
  if (ev.getAction() == MotionEvent.ACTION_DOWN) {
    onUserInteraction();
  }
  if (getWindow().superDispatchTouchEvent(ev)) {
    return true;
  }
  return onTouchEvent(ev);
}

//Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {
  //Throw away all previous state when starting a new touch gesture.
  //The framework may have dropped the up or cancel event for the previous gesture due to an app switch, ANR, or some other state change.
  cancelAndClearTouchTargets(ev);
  resetTouchState();
}

final boolean canceled = resetCancelNextUpFlag(this) || actionMasked == MotionEvent.ACTION_CANCEL;
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) {
  // 不是ACTION_CANCEL并且不拦截
  if (actionMasked == MotionEvent.ACTION_DOWN) {
     // 若当前事件为ACTION_DOWN则去寻找这次事件新出现的touch target
     final int actionIndex = ev.getActionIndex(); // always 0 for down
 
     ...
 
     final int childrenCount = mChildrenCount;
     if (newTouchTarget == null && childrenCount != 0) {
       // 根据触摸的坐标寻找能够接收这个事件的touch target
       final float x = ev.getX(actionIndex);
       final float y = ev.getY(actionIndex);
 
       final View[] children = mChildren;
       // 遍历所有子View
       for (int i = childrenCount - 1; i >= 0; i--) {
         final int childIndex = i;
         final View child = children[childIndex];
         // 寻找可接收这个事件并且touch事件坐标在其区域内的子View
         if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) {
           continue;
         }
 
         newTouchTarget = getTouchTarget(child); // 找到了符合条件的子View，赋值给newTouchTarget
         if (newTouchTarget != null) {
           //Child is already receiving touch within its bounds.
           //Give it the new pointer in addition to ones it is handling.
           newTouchTarget.pointerIdBits |= idBitsToAssign;
           break;
         }
         resetCancelNextUpFlag(child);
         // 把ACTION_DOWN事件传递给子组件进行处理
         if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
           //Child wants to receive touch within its bounds.
           mLastTouchDownTime = ev.getDownTime();
           if (preorderedList != null) {
             //childIndex points into presorted list, find original index
             for (int j=0;j<childrenCount;j++) {
               if (children[childIndex]==mChildren[j]) {
                 mLastTouchDownIndex=j;
                 break;
               }
             }
           } else {
             mLastTouchDownIndex = childIndex;
           }
           mLastTouchDownX = ev.getX();
           mLastTouchDownY = ev.getY();
           //把mFirstTouchTarget赋值为newTouchTarget，此子View成为新的touch事件的起点
           newTouchTarget = addTouchTarget(child, idBitsToAssign);
           alreadyDispatchedToNewTouchTarget = true;
           break;
         }           
       }
     }
  }
}

if (child == null) {
  handled = super.dispatchTouchEvent(event);
} else {
  handled = child.dispatchTouchEvent(event);
}

if (mFirstTouchTarget == null) {
  handled = dispatchTransformedTouchEvent(ev, canceled, null, TouchTarget.ALL_POINTER_IDS);
}

public boolean dispatchTouchEvent(MotionEvent event) {
  boolean result = false;
  . . .
   
  if (onFilterTouchEventForSecurity(event)) {
    //noinspection SimplifiableIfStatement
    ListenerInfo li = mListenerInfo;
    if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED
        && li.mOnTouchListener.onTouch(this, event)) {
      result = true;
    }
     
    if (!result && onTouchEvent(event)) {
      result = true;
    }
    . . .
    return result;
}

if (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
  switch (event.getAction()) {
    case MotionEvent.ACTION_UP:
      boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
      if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
        . . .
        if (!mHasPerformedLongPress) {
          //This is a tap, so remove the longpress check 
          removeLongPressCallback();
           
          //Only perform take click actions if we were in the pressed state
          if (!focusTaken) {
            //Use a Runnable and post this rather than calling performClick directly.
            //This lets other visual state of the view update before click actions start.
            if (mPerformClick == null) {
              mPerformClck = new PeformClick();
            }
            if (!post(mPerformClick)) {
              performClick();
            }
          }
        }
        . . .
      }
      break;
  }
  . . .
  return true;
}

public boolean performClick() {
  final boolean result;
  final ListenerInfo li = mListenerInfo;
  if (li != null && li.mOnClickListener != null) {
    playSoundEffect(SoundEffectConstants.CLICK);
    li.mOnClickListener.onClick(this);
    result = true;
  } else {
    result = false;
  }
  sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
  return result;
}