/// <summary>
  /// 開始捕捉
  /// </summary>
  /// <param name="sender"></param>
  /// <param name="e"></param>
  private void btnStart_Click(object sender, EventArgs e)
  {
   if (this.combDevice.SelectedIndex > -1)
   {
    StartCapture(this.combDevice.SelectedIndex);
    this.btnStart.Enabled = false;
    this.btnStop.Enabled = true;
   }
   else {
    MessageBox.Show(this,"請選擇一個設備","提示",MessageBoxButtons.OK);
   }
  }

  /// <summary>
  /// 停止捕捉
  /// </summary>
  /// <param name="sender"></param>
  /// <param name="e"></param>
  private void btnStop_Click(object sender, EventArgs e)
  {
   Shutdown();
   this.btnStop.Enabled = false;
   this.btnStart.Enabled = true;
  }

  private void StartCapture(int itemIndex)
  {
   packetCount = 0;
   device = CaptureDeviceList.Instance[itemIndex];
   packetStrings = new Queue<PacketWrapper>();
   bs = new BindingSource();
   dgvData.DataSource = bs;
   LastStatisticsOutput = DateTime.Now;

   // start the background thread
   backgroundThreadStop = false;
   backgroundThread = new Thread(BackgroundThread);
   backgroundThread.Start();

   
   // setup background capture
   device.OnPacketArrival += new PacketArrivalEventHandler(device_OnPacketArrival);
   device.OnCaptureStopped += new CaptureStoppedEventHandler(device_OnCaptureStopped);
   device.Open();

   // tcpdump filter to capture only TCP/IP packets
   string filter = "ip and tcp";
   device.Filter = filter;

   // force an initial statistics update
   captureStatistics = device.Statistics;
   UpdateCaptureStatistics();

   // start the background capture
   device.StartCapture();

   btnStop.Enabled = true;
  }

  /// <summary>
  /// 設備接收事件
  /// </summary>
  /// <param name="sender"></param>
  /// <param name="e"></param>
  private void device_OnPacketArrival(object sender, CaptureEventArgs e)
  {
   // print out periodic statistics about this device
   var Now = DateTime.Now;
   var interval = Now - LastStatisticsOutput;
   if (interval > new TimeSpan(0, 0, 2))
   {
    Console.WriteLine("device_OnPacketArrival: " + e.Device.Statistics);
    captureStatistics = e.Device.Statistics;
    statisticsUiNeedsUpdate = true;
    LastStatisticsOutput = Now;
   }
   
   lock (QueueLock)
   {
    PacketQueue.Add(e.Packet);
   }
  }

  /// <summary>
  /// 設備停止事件
  /// </summary>
  /// <param name="sender"></param>
  /// <param name="status"></param>
  private void device_OnCaptureStopped(object sender, CaptureStoppedEventStatus status)
  {
   if (status != CaptureStoppedEventStatus.CompletedWithoutError)
   {
    MessageBox.Show("Error stopping capture", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
   }
  }

  private void UpdateCaptureStatistics()
  {
   tlblStatistic.Text = string.Format("接收包: {0}, 丟棄包: {1}, 接口丟棄包: {2}", captureStatistics.ReceivedPackets,captureStatistics.DroppedPackets, captureStatistics.InterfaceDroppedPackets);
  }