ViewDragHelper.CallBack中方法回调

    //view是否可以拖动
   override fun tryCaptureView(child: View, pointerId: Int): Boolean {
      return true
    }
    //水平方向滑动距离Return the magnitude of a draggable child view's horizontal range of motion in pixels.This method should return 0 for views that cannot move vertically.
    override fun clampViewPositionHorizontal(child: View, left: Int, dx: Int): Int {
      return left
    }
    //垂直方向的滑动距离Return the magnitude of a draggable child view's vertical range of motion in pixels.This method should return 0 for views that cannot move vertically.
    override fun clampViewPositionVertical(child: View, top: Int, dy: Int): Int {
      return top
    }
    //捕获子视图Called when a child view is captured for dragging or settling.
    override fun onViewCaptured(capturedChild: View, activePointerId: Int) {
      capturedChild.elevation = elevation + 1
      capturedLeft = capturedChild.left.toFloat()
      capturedTop = capturedChild.top.toFloat()
    }
    //view位置改变时候Called when the captured view's position changes as the result of a drag or settle.
    override fun onViewPositionChanged(changedView: View, left: Int, top: Int, dx: Int, dy: Int) {
    }
    //拖拽结束Called when the child view is no longer being actively dragged.
    override fun onViewReleased(releasedChild: View, xvel: Float, yvel: Float) {
      dragHelper.settleCapturedViewAt(capturedLeft.toInt(), capturedTop.toInt())
      postInvalidateOnAnimation()
    }