Android：如何关联来自同一拖动动作的ACTION_DOWN和ACTION_MOVE事件

Question

I want to allow the user to drag controls vertically in my OpenGL view (like a scrollbar). To implement this I plan to do the following:

• Use onTouchEvent to listen for motion events
• On ACTION_DOWN , record the vertical offset between the touch location and the control
• On ACTION_MOVE , inch the control upwards/downwards depending on which way the user drags
• On ACTION_UP , delete the offset

I want to support the user dragging multiple controls at the same time, so I need to be able to get some kind of ID from the ACTION_DOWN event that I can use as the hashtable entry for the offset. Later, when handling ACTION_MOVE I need to be able to get that same ID to look up the offset in the hashtable, in order to ensure that we don't mix up 2 controls that are being dragged at the same time. How do I get this 'ID' so I can correlate the ACTION_DOWN and ACTION_MOVE events that come from the same drag motion?

Answer 1

原来MotionEvent.downTime是我一直在寻找的属性。