Pass MotionEvent to GridView

Question

Here is a summary of what i m trying to achieve. I have a view, on that view i m listening for MotionEvent. When it matches a specific condition, i would like to pass that MotionEvent to a GridView, in order to scroll. I m doing something like

if (event.getAction() == MotionEvent.ACTION_MOVE) {
    if (condition match) {
        getGridView().dispatchTouchEvent(event);
    }
}

But it does not make my grid scrolling according to the MotionEvent. Maybe it's not listening for that kind of event but since there is not "ScrollEvent" i don't know.

Can anyone please enlight me about that. I didn't find the doc helpfull. Thank you.

Answer 1

In order to process motion events a view needs to get the full set of events related to that movement.

For example, a scroll should start with MotionEvent.ACTION_DOWN , followed by several MotionEvent.ACTION_MOVE and finalized with a MotionEvent.ACTION_UP. You can't just dispatch one of these events, the full set need to be dispatched for the view to be able to decode the scroll movement.

Regards.

Answer 2

Luis have explained the reason why your grid view doesn't scroll. In fact such dispatch is not correct. You said that you want to pass the MotionEvent of View A to View B. But the x and y in a motion is relative to the view, and cannot be used directly in another view. Try to look the source code of ViewGroup.dispatchTouchEvent(), ViewGroup will transform a motion before it is dispatched to a child. If View B is a child of View A, you should use onInterceptTouchEvent() to intercept the motion , instead of changing the dispatch mechanism.