【android】說說GestureDetector.OnGestureListener onScroll函數

public abstract boolean onScroll (MotionEvent e1, MotionEvent e2,
float distanceX, float distanceY)Since: API Level 1

Notified when a scroll occurs with the initial on down MotionEvent and
the current move MotionEvent. The distance in x and y is also
supplied for convenience.

Parameters

e1	The first down motion event that started the scrolling.
e2	The move motion event that triggered the current onScroll.
distanceX	The distance along the X axis that has been scrolled since the last call to onScroll. This is NOT the distance between e1 and e2.
distanceY	The distance along the Y axis that has been scrolled since the last call to onScroll. This is NOT the distance between e1 and e2.

Returns

• true if the event is consumed, else false

e1 初次觸控地圖的event1e2 每次觸發onScroll函數得到的的event2 distance是上一次的event2 減去 當前event2得到的結果
//注意到順序 lastEvent2 - event2 = distance
驗證：

if (lastE2 != null){    Log.i(TAG, "distanceX:" + distanceX + " = " + (lastE2.getX()-e2.getX()));    Log.i(TAG, "distanceY:" + distanceY + " = " + (lastE2.getY()-e2.getY()));}lastE2 = MotionEvent.obtain(e2);