关于GestureDetector.OnGestureListener类的onScroll方法参数distanceX和distanceY问题
看到有文章上说onScroll方法中distanceX和distanceY是指“distanceX，是前后两次call的X距离，不是e2与e1的水平距离； 是前后两次call的Y距离，不是e2与e1的垂直距离”
然后怎么也没理解出来这两个参数是什么意思
于是去实践了一下：
以下是谷歌官方API说明：
public abstract boolean onScroll (MotionEvent e1, MotionEvent e2, float distanceX, float distanceY)
Added in 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
“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.”
这句话按我自己翻译出来的意思是“在上一次（最后一次）调用onScroll方法沿着X轴所滑动的距离。不是e1和e2之间的距离”
我的理解是：distanceX是滑动起点和终点的水平距离，而不是起点和终点的直线距离。
写了个例子在LogCat中输出了一下它们的值：
发现
distanceX的值等于e1的X值减去e2的X值，计算结果带正负号。
distanceY的值等于e1的Y值减去e2的Y值，计算结果带正负号。
不知道这理解正不正确，如有错误望指正。