What causes a MotionEvent.ACTION_CANCEL in Android?

user_763080 0
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I am working through debugging some touch handling stuff on Android, and am trying to figure out why the MotionEvent sent to my View's onTouchListener contains a cancel action. I have not been able to find any documentation on its cause, and was hoping someone could point me in the right direction for debugging this problem - error codes, source code, or some general knowledge.

motionevent android debugging
5 Answers

All you need is to call 

requestDisallowInterceptTouchEvent(true);

on the parent view, like this - 

        @Override
        public boolean onTouch(View view, MotionEvent motionEvent) {
            view.getParent().requestDisallowInterceptTouchEvent(true);
            switch(motionEvent.getActio){
            }

            return false; 

         }

Source: onInterceptTouchEvent, onTouchEvent only see ACTION_DOWN

user_63275540

ACTION_CANCEL is triggered by ancestor to notify all descendants that they lost onTouch control and it's will be responsible for handling the next onTouch event. Usually it is caused when a descendant returned true in onTouch or onTouchEvent method but after that, during the next of touch event of gesture, an ancestor returned true in onInterceptTouchEvent()

[Touch event flow]

user_47708770

In my situation, TouchDelegate helped.

https://medium.com/android-news/android-change-touch-area-of-view-by-touchdelegate-fc19f2a34021

private fun changeTouchableAreaOfView(view: View, extraSpace: Int) {
val parent = view.parent as View
Observable.just(parent)
        .observeOn(AndroidSchedulers.mainThread())
        .subscribeOn(AndroidSchedulers.mainThread())
        .subscribe {
            val touchableArea = Rect()
            view.getHitRect(touchableArea)
            touchableArea.top -= extraSpace
            touchableArea.bottom += extraSpace
            touchableArea.left -= extraSpace
            touchableArea.right += extraSpace
            parent.touchDelegate = TouchDelegate(touchableArea, button)
        }

/* In case you don't want to use Rx java
parent.post {
    val touchableArea = Rect()
    button.getHitRect(touchableArea)
    touchableArea.top -= extraSpace
    touchableArea.bottom += extraSpace
    touchableArea.left -= extraSpace
    touchableArea.right += extraSpace
    parent.touchDelegate = TouchDelegate(touchableArea, button)
}
*/

}

user_101490740
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