C# 统制 WndProc()接收处理消息的频率

C# 控制 WndProc()接收处理消息的频率
      我用终端机扫描信息后 打印扫描的信息  但是由于机器太灵敏   他会出现一秒内扫描很多次 导致会打印出多条 一样的信息
  我现在想10秒内 只能处理一次 该怎么弄？。
代码如下： 

DateTime? lastScanTime = null;

            protected override void WndProc(ref Message msg)

        {

           try

            {

               

                if (lastScanTime == null)

                {

                    lastScanTime = DateTime.Now;

                }

                else

                {

                    TimeSpan span = DateTime.Now - lastScanTime.Value;

                    if (span.Seconds < 10)

                        return;

                }

               

                    if (msg.Msg == WM_SCANCODE_ENGINE_NOTIFY)   // BarCode的自定义消息通知

                    {

                     

                        uint nDataLen = 0; //= (int)msg.WParam;

                        uint nBarCodeType = 0;// = (uint)msg.LParam;

                        byte[] BarCodeData;

                        barcode.GetBarCodeReaderRes(ref nBarCodeType, ref  nDataLen, null);

                        if (nDataLen > 0)

                        {

                           

                            string mess = "正在处理";

                            BarCodeData = new byte[nDataLen];

                            barcode.GetBarCodeReaderRes(ref nBarCodeType, ref  nDataLen, BarCodeData);

                            string str1 = Encoding.Default.GetString(BarCodeData, 0, (int)nDataLen);

                            this._BaseForm.DecodeText(ref mess);

                            this._BaseForm.GetTick(str1, 1);

                            barcode.DoBeep(1, 50, 80);

                          

                        }

                        if (_BaseForm.PrintMessage != "" && _BaseForm.isScan)