Onintercepttouchevent Only Gets Action_Down

onInterceptTouchEvent only gets ACTION_DOWN

I'll answer my own question: onInterceptTouchEvent only get called if the parent has a child view which returns "true" from onTouchEvent. Once the child returns true, the parent now has a chance to intercept that event.

onInterceptTouchEvent never receives action_move

It's a bit more complicated than that. First of all you need to override onTouchEvent() and handle ACTION_DOWN and MOVE events there too. Then the following will happen.

1. ACTION_DOWN event gets dispatched to onInterceptTouchEvent() first. You should return false from there.
2. Now there are two cases:
   
   
   • If there is no touchable view underneath ACTION_DONW event's location in the view tree, then ACTION_DOWN event and all follow up events get dispatched to onTouchEvent(). You must return true from there. Only then you will receive follow up events sent to onTouchEvent() method. Independently on whether you return true or false, onInterceptTouchEvent() will not receive any follow up events anymore.
   • If there is a touchable view, then all events will be dispatched to onInterceptTouchEvent() (including ACTION_MOVE events). You need to return true from there, after you detected your gesture. Once you return true from here, touchable view will receive ACTION_CANCEL event and all further events will be dispatched to onTouchEvent() method.

Hope this helps.

Android onInterceptTouchEvent doesn't get action when have child view

The solution relates to this answer, as it is a result of the standard MotionEvent handling.

In my code, when I touch the child LinearLayout, the parent CustomViewGroup doesn't intercept the MotionEvent as it returns false, but my child LinearLayout doesn't consume the MotionEvent either, so the MotionEvent is returned to the parent's onTouchEvent, not onInterceptTouchEvent.

On the other hand, when I touch my child ScrollView, it consumes the MotionEvent whether scrolling is enabled or disabled.

==> I think because Android doesn't generate a MotionEvent again until the original one is either consumed or finished, so the parent CustomViewGroup doesn't get the ACTION_MOVE MotionEvent via onInterceptTouchEvent, instaed it is piped to onTouchEvent when a child doesn't consume the MotionEvent.

I found two solutions

Solution one

Forcibly make my LinearLayout consume the MotionEvent. This solution is available only when the child LinearLayout has no touchable View, ViewGroup or Widget. Like this:

LinearLayout mLinearLayout = (LinearLayout)findViewById(R.id.child_linear);
mLinearLayout.setOnTouchListener(new OnTouchListener() {
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        return true;
    }
});

Solution two

Process the MotionEvent returning from a child in my CustomViewGroup's onTouchEvent. Like this: (Just add else if case in onTouchEvent).

case MotionEvent.ACTION_MOVE: {
    if (mIsBeingDragged) {
        mLastMotionY = event.getY();
        mLastMotionX = event.getX();
        pullEvent();
        return true;
    }
    else if (isReadyForPull()) {
        final float y = event.getY(), x = event.getX();
        final float diff, oppositeDiff, absDiff;
        diff = y - mLastMotionY;
        oppositeDiff = x - mLastMotionX;
        absDiff = Math.abs(diff);
        ViewConfiguration config = ViewConfiguration.get(getContext());

        if (absDiff > config.getScaledTouchSlop() &&  absDiff > 
        Math.abs(oppositeDiff) && diff >= 1f) {
             mLastMotionY = y;
             mLastMotionX = x;
             mIsBeingDragged = true;
        }
     }
     break;
 }

While solution 1 is a quick fix for certain situations, solution two is the most flexible and reliable.

onInterceptTouchEvent's ACTION_UP and ACTION_MOVE never gets called

Your onInterceptTouchEvent method is not called after ACTION_DOWN event because you return true in onTouchEvent method. So all the other events are sent in onTouchEvent and not in onInterceptTouchEvent any more:

Using this function takes some care, as it has a fairly complicated
interaction with View.onTouchEvent(MotionEvent), and using it requires
implementing that method as well as this one in the correct way.
Events will be received in the following order:

You will receive the down event here. The down event will be handled
either by a child of this view group, or given to your own
onTouchEvent() method to handle; this means you should implement
onTouchEvent() to return true, so you will continue to see the rest of
the gesture (instead of looking for a parent view to handle it). Also,
by returning true from onTouchEvent(), you will not receive any
following events in onInterceptTouchEvent() and all touch processing
must happen in onTouchEvent() like normal.

http://developer.android.com/reference/android/view/ViewGroup.html#onInterceptTouchEvent(android.view.MotionEvent)

Losing ACTION_DOWN parameters when InterceptTouchEvent

Just expose your mStartX to your activity. ( I know it not perfect but seems OK).

class ParentView extends ViewGroup (or some other viewGroup) {
    int startX;
    public int getStartX(){
        return startX;
    }
}

// After that just call getStartX() from your activity.

View.onTouchEvent only registers ACTION_DOWN event

You need to return true to get the following events after a down.

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