Android项目中怎么实现一个可拖拽界面

/**
 * 可拖拽ImageView
 * Created by admin on 2017/2/21.
 */
public class FloatingImageView extends ImageView{
  public FloatingImageView(Context context) {
    super(context);
  }
  public FloatingImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
  }
  public FloatingImageView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
  }
  @TargetApi(Build.VERSION_CODES.LOLLIPOP)
  public FloatingImageView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
    super(context, attrs, defStyleAttr, defStyleRes);
  }
  int startX;
  int startY;
  int left;
  int top;
  int[] temp = new int[]{ 0, 0 };
  @Override
  public boolean onTouchEvent(MotionEvent event) {
    boolean isMove = false;
    int x = (int) event.getRawX();
    int y = (int) event.getRawY();
    switch (event.getAction()){
      case MotionEvent.ACTION_DOWN: // touch down so check if the
        startX = x;
        startY = y;
        temp[0] = (int) event.getX();
        temp[1] = y - getTop();
        break;
      case MotionEvent.ACTION_MOVE: // touch drag with the ball
        left = x - temp[0];
        top = y - temp[1];
        if(left < 0){//控制左边界不超出
          left = 0;
        }
        layout(left, top, left + getWidth(),top + getHeight());//自由拖拽
        break;
      case MotionEvent.ACTION_UP:
        if (Math.abs(x - startX) > 2 || Math.abs(y - startY) > 2){//判断是否移动,再一定范围内不算是移动，解决触发事件冲突
          //将最后拖拽的位置定下来，否则页面刷新渲染后按钮会自动回到初始位置
          //注意父容器
          RelativeLayout.LayoutParams lp = (RelativeLayout.LayoutParams) getLayoutParams();
          lp.setMargins(left, top,0,0);
          setLayoutParams(lp);
          //确定是拖拽
          isMove = true;
         }
        break;
    }
    return isMove ? true : super.onTouchEvent(event);
   }
}