private void Form1_MouseDown(object sender, MouseEventArgs e)

写了一个form1_MouseDown,鼠标在form1上移动不知道怎么没反映
private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            Point mouseDownLocation = new Point(e.X ,e.Y );
            string eventString =null;
            switch (e.Button)
            {
                case MouseButtons .Left :
                eventString ="L";
                    break ;
                case MouseButtons .Right :
                    eventString ="R";
                    break ;
                case MouseButtons .Middle :
                    eventString ="M";
                    break;
                case MouseButtons .XButton1 :
                    eventString = "X1";
                    break;
                case MouseButtons .XButton2 :
                    eventString ="X2";
                    break;
                default :
                    break;                    
            
            
            
            }
            if (eventString != null)
            {
                this.toolStripStatusLabel1.Text = "当前鼠标位置:" + eventString.ToString() + "鼠标落下位置" + mouseDownLocation.ToString();            }
            else
            {                this.toolStripStatusLabel1.Text  = mouseDownLocation.ToString();
            
            }
        
        
        }