深入解析Andoird应用开发中View的事件传递

public boolean dispatchTouchEvent(MotionEvent event) {
 if (mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED &&
   mOnTouchListener.onTouch(this, event)) {
   return true;
 }
 return onTouchEvent(event);
}

if (((viewFlags & CLICKABLE) == CLICKABLE || 
   (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) { 
  switch (event.getAction()) { 
   case MotionEvent.ACTION_UP:
    ..... 
      performClick(); //响应点击事件 
    break; 
   case MotionEvent.ACTION_DOWN: 
   ..... break; 
   case MotionEvent.ACTION_CANCEL: 
   ..... break; 
   case MotionEvent.ACTION_MOVE: 
   ..... break; 
  } 
  return true; 
} 
return false;

public boolean performClick() {
  sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
  if (mOnClickListener != null) {
     playSoundEffect(SoundEffectConstants.CLICK);
     mOnClickListener.onClick(this);
     return true;
  }
  return false;
}

public boolean dispatchTouchEvent(MotionEvent ev) {

  boolean handled = false;
  if (onFilterTouchEventForSecurity(ev)) {
    final int action = ev.getAction();
    final int actionMasked = action & MotionEvent.ACTION_MASK;

    // Attention 1 ：在按下时候清除一些状态
    if (actionMasked == MotionEvent.ACTION_DOWN) {
      cancelAndClearTouchTargets(ev);
      //注意这个方法
      resetTouchState();
    }

    // Attention 2：检查是否需要拦截
    final boolean intercepted;
    //如果刚刚按下 或者 已经有子View来处理
    if (actionMasked == MotionEvent.ACTION_DOWN
        || mFirstTouchTarget != null) {
      final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
      if (!disallowIntercept) {
        intercepted = onInterceptTouchEvent(ev);
        ev.setAction(action); // restore action in case it was changed
      } else {
        intercepted = false;
      }
    } else {
      // 不是一个动作序列的开始 同时也没有子View来处理，直接拦截
      intercepted = true;
    }

     //事件没有取消 同时没有被当前ViewGroup拦截，去找是否有子View接盘
    if (!canceled && !intercepted) {
        //如果这是一系列动作的开始 或者有一个新的Pointer按下 我们需要去找能够处理这个Pointer的子View
      if (actionMasked == MotionEvent.ACTION_DOWN
          || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
          || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
        final int actionIndex = ev.getActionIndex(); // always 0 for down

        //上面说的触碰点32的限制就是这里导致
        final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
            : TouchTarget.ALL_POINTER_IDS;

        final int childrenCount = mChildrenCount;
        if (newTouchTarget == null && childrenCount != 0) {
          final float x = ev.getX(actionIndex);
          final float y = ev.getY(actionIndex);

          //对当前ViewGroup的所有子View进行排序，在上层的放在开始
          final ArrayList<View> preorderedList = buildOrderedChildList();
          final boolean customOrder = preorderedList == null
              && isChildrenDrawingOrderEnabled();
          final View[] children = mChildren;
          for (int i = childrenCount - 1; i >= 0; i--) {
            final int childIndex = customOrder
                ? getChildDrawingOrder(childrenCount, i) : i;
            final View child = (preorderedList == null)
                ? children[childIndex] : preorderedList.get(childIndex);

               // canViewReceivePointerEvents visible的View都可以接受事件
               // isTransformedTouchPointInView 计算是否落在点击区域上
            if (!canViewReceivePointerEvents(child)
                || !isTransformedTouchPointInView(x, y, child, null)) {
              ev.setTargetAccessibilityFocus(false);
              continue;
            }

               //能够处理这个Pointer的View是否已经处理之前的Pointer，那么把
            newTouchTarget = getTouchTarget(child);
            if (newTouchTarget != null) {
              // Child is already receiving touch within its bounds.
              // Give it the new pointer in addition to the ones it is handling.
              newTouchTarget.pointerIdBits |= idBitsToAssign;
              break;
            }              }
            //Attention 3 : 直接发给子View
            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();
              newTouchTarget = addTouchTarget(child, idBitsToAssign);
              alreadyDispatchedToNewTouchTarget = true;
              break;
            }

          }
        }

      }
    }

    // 前面已经找到了接收事件的子View，如果为NULL，表示没有子View来接手，当前ViewGroup需要来处理
    if (mFirstTouchTarget == null) {
      // ViewGroup处理
      handled = dispatchTransformedTouchEvent(ev, canceled, null,
          TouchTarget.ALL_POINTER_IDS);
    } else {

        if(alreadyDispatchedToNewTouchTarget) {
                   //ignore some code
          if (dispatchTransformedTouchEvent(ev, cancelChild,
              target.child, target.pointerIdBits)) {
            handled = true;
         }
        }

    }
  return handled;
}

dispatchTransformedTouchEvent
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
    View child, int desiredPointerIdBits) {

   //没有子类处理，那么交给viewgroup处理
  if (child == null) {
    handled = super.dispatchTouchEvent(transformedEvent);
  } else {
    final float offsetX = mScrollX - child.mLeft;
    final float offsetY = mScrollY - child.mTop;
    transformedEvent.offsetLocation(offsetX, offsetY);
    if (! child.hasIdentityMatrix()) {
      transformedEvent.transform(child.getInverseMatrix());
    }

    handled = child.dispatchTouchEvent(transformedEvent);
  }
  return handled;
}

dispatchTouchEvent
  public boolean dispatchTouchEvent(MotionEvent event) {
    if (onFilterTouchEventForSecurity(event)) {
    //先走View的onTouch事件，如果onTouch返回True
    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;
  }