MotionEvent中的ACTION_CANCEL和ACTION_UP有什么区别？

Question

I want to track a finger touch on the screen. So what I did was to start recording the position when MotionEvent triggers ACTION_DOWN , but how do I know when the action is finished, at ACTION_CANCEL , or ACTION_UP ?

What's the exact difference between them?

Answer 1

MotionEvent:

• ACTION_UP: A pressed gesture has finished, the motion contains the final release location as well as any intermediate points since the last down or move event.

• ACTION_CANCEL: The current gesture has been aborted.

ACTION_CANCEL occurs when the parent takes possession of the motion, for example when the user has dragged enough across a list view that it will start scrolling instead of letting you press the buttons inside of it. You can find out more about it at the viewgroup documentation: onInterceptTouchEvent .

so use ACTION_CANCEL when the action is dragged out of the parent, and ACTION_UP otherwise.

Answer 2

In general ACTION_UP is triggered by user when the guest is finished to definitely indicate that the user completed interacting with movement.

On the other hand ACTION_CANCEL is called by system to show that a parent view takes over control of one of its children views.

Please take a look at a diagram