public void OnDrag(PointerEventData eventData)

{

    Vector2 targetDir = eventData.position - new Vector2(transform.position.x, transform.position.y); // 目标坐标与当前坐标差的向量

　　 float ang = Vector2.Angle(Vector3.right, targetDir); // 返回当前坐标与目标坐标的角度

    if (eventData.position.y <transform.position.y)
 　　{ 
　　　　ang =  - ang; 
　　　} 
　　　transform.localEulerAngles = new Vector3(, , ang); 

 }

  public void OnDrag(PointerEventData eventData)

    {

        Camera camera = GameObject.Find("Main Camera").GetComponent<Camera>();

        Vector3 screenPos = camera.WorldToScreenPoint(transform.position);//世界坐标转屏幕坐标

        Vector2 targetDir = eventData.position - new Vector2(screenPos.x, screenPos.y);// 目标坐标与当前坐标差的向量

float ang = Vector2.Angle(Vector3.right, targetDir); // 返回当前坐标与目标坐标的角度

        if (eventData.position.y < screenPos.y)

        {

            ang =  - ang;

        }

        transform.localEulerAngles = new Vector3(, , ang);

    }