SerialPort串口通讯中DataReceived事件不能触发

  //定义串口
        private SerialPort comm;     
        private long received_count = 0;//接收计数
        private long send_count = 0;//发送计数
        byte c = 51;
        public Form1()
        {
            InitializeComponent();
           
             
        
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            
            comm = new SerialPort("COM4", 1200);
           
            //添加事件注册
            comm.DataReceived += comm_DataReceived;
            comm.ReceivedBytesThreshold = 1;
            
        }

        //数据接收
        void comm_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            int n = comm.BytesToRead;//先记录下来，避免某种原因，人为的原因，操作几次之间时间长，缓存不一致
            byte[] buf = new byte[n];//声明一个临时数组存储当前来的串口数据
            received_count += n;//增加接收计数
            comm.Read(buf, 0, n);//读取缓冲数据          
            //因为要访问ui资源，所以需要使用invoke方式同步ui。
            this.Invoke((EventHandler)(delegate
            {
                //依次的拼接出16进制字符串   
                string ReceivedStr = GetHexStrFromByte(buf);                
                this.label1.Text = GetAm(ReceivedStr);
               
                
            }));
        }