Android事件分发机制 Android事件分发机制（上) ViewGroup的事件分发

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

public boolean superDispatchTouchEvent(MotionEvent event) {
 return mDecor.superDispatchTouchEvent(event);
}

public boolean superDispatchTouchEvent(MotionEvent event) {
 return super.dispatchTouchEvent(event);
}

// 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();
}

private TouchTarget mFirstTouchTarget;

......

private void cancelAndClearTouchTargets(MotionEvent event) {
 if (mFirstTouchTarget != null) {
 boolean syntheticEvent = false;
 if (event == null) {
  final long now = SystemClock.uptimeMillis();
  event = MotionEvent.obtain(now, now,
   MotionEvent.ACTION_CANCEL, 0.0f, 0.0f, 0);
  event.setSource(InputDevice.SOURCE_TOUCHSCREEN);
  syntheticEvent = true;
 }

 for (TouchTarget target = mFirstTouchTarget; target != null; target = target.next) {
  resetCancelNextUpFlag(target.child);
  dispatchTransformedTouchEvent(event, true, target.child, target.pointerIdBits);
 }
 clearTouchTargets();

 if (syntheticEvent) {
  event.recycle();
 }
 }
}

private void resetTouchState() {
 clearTouchTargets();
 resetCancelNextUpFlag(this);
 mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
 mNestedScrollAxes = SCROLL_AXIS_NONE;
}

// Check for interception.
final boolean intercepted;
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 {
 // There are no touch targets and this action is not an initial down
 // so this view group continues to intercept touches.
 intercepted = true;
}

final int childrenCount = mChildrenCount;
if (newTouchTarget == null && childrenCount != 0) {
 final float x = ev.getX(actionIndex);
 final float y = ev.getY(actionIndex);
 // Find a child that can receive the event.
 // Scan children from front to back.
 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);

 // If there is a view that has accessibility focus we want it
 // to get the event first and if not handled we will perform a
 // normal dispatch. We may do a double iteration but this is
 // safer given the timeframe.
 if (childWithAccessibilityFocus != null) {
  if (childWithAccessibilityFocus != child) {
  continue;
  }
  childWithAccessibilityFocus = null;
  i = childrenCount - 1;
 }

 if (!canViewReceivePointerEvents(child)
  || !isTransformedTouchPointInView(x, y, child, null)) {
  ev.setTargetAccessibilityFocus(false);
  continue;
 }

 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;
 }

 resetCancelNextUpFlag(child);
 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;
 }

 // The accessibility focus didn't handle the event, so clear
 // the flag and do a normal dispatch to all children.
 ev.setTargetAccessibilityFocus(false);
 }
 if (preorderedList != null) preorderedList.clear();
}

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

if (mFirstTouchTarget == null) {
 // No touch targets so treat this as an ordinary view.
 handled = dispatchTransformedTouchEvent(ev, canceled, null,
  TouchTarget.ALL_POINTER_IDS);
}