MotionEvent事件-控件随手指拖动 限制控件的滑动位置

private int lastX;
private int lastY;
private int maxRight;
private int maxBottom;

@Override
public boolean onTouch(View v, MotionEvent event) {
    //getRawX()是控件相对于父容器左上角的距离
    //获取控件的x,y坐标
    int eventX = (int) event.getRawX();
    int eventY = (int) event.getRawY();


    switch (event.getAction()) {

        case MotionEvent.ACTION_DOWN:
            //得到imageview的父容器
            LinearLayout viewParent = (LinearLayout) mImageView.getParent();
            if (maxRight == 0) {//这个判断 保证值给max赋值一次
                maxRight = viewParent.getRight();
                maxBottom = viewParent.getBottom();
            }

            /**记录控件的x,y坐标*/
            lastX = eventX;
            lastY = eventY;

            break;

        case MotionEvent.ACTION_MOVE:
            /**计算偏移量*/
            int dx = eventX - lastX;
            int dy = eventY - lastY;

            /**根据事件的偏移量来移动控件*/
            int left = mImageView.getLeft() + dx;
            int top = mImageView.getTop() + dy;
            int right = mImageView.getRight() + dx;
            int buttom = mImageView.getBottom() + dy;

            //限制left
            if (left < 0) {
                right += (-left);
                left = 0;
            }

            //限制top
            if (top < 0) {
                buttom += (-top);
                top = 0;
            }

            //限制right
            if (right > maxRight) {
                left -= (right - maxRight);
                right = maxRight;
            }

            //限制bottom
            if (buttom > maxBottom) {
                top -= (buttom - maxBottom);
                buttom = maxBottom;
            }

            mImageView.layout(left, top, right, buttom);

            /**再次记录控件的x,y坐标*/
            lastX = eventX;
            lastY = eventY;

            break;

        default:
            break;
    }
        return true;/**所有的motionevent都交给imageview来处理*/
}