C# SharpPcap Cross-thread operation not valid

Question

Hi I'm trying to convert packet capturing in Example3 in SharpPcap new version SharpPcap-2.2.0rc1.src from Console Application to Windows Forms Application.

I'm facing a problem when I tried to add packets has been captured to ListView control I will get an error which is:

(Cross-thread operation not valid: Control 'listViewPackets' accessed from a thread other than the thread it was created on.)

at this line:
listViewPackets.Items.Add(e.Packet.ToString());

any Advice to solve this problem???

here is my code:

using SharpPcap;

namespace Packets
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }



            // Retrieve the device list

        private void btnLiDevicest_Click(object sender, EventArgs e)
        {
            var devices = LivePcapDeviceList.Instance;
            // If no devices were found print an error
            if (devices.Count < 1)
            {
                MessageBox.Show("No devices were found on this machine");
                return;
            }


            int i = 0;

            // Print out the devices
            foreach (LivePcapDevice dev in devices)
            {

                ///* Description */
                //Console.WriteLine("{0}) {1} {2}", i, dev.Name, dev.Description);
                cmbListDevice.Items.Add(dev.Name + "   " + dev.Description);
                i++;
            }
           LivePcapDevice device = devices[1];
            // Register our handler function to the 'packet arrival' event
            device.OnPacketArrival += new PacketArrivalEventHandler(device_OnPacketArrival);

            // Open the device for capturing
            int readTimeoutMilliseconds = 1000;
            device.Open(DeviceMode.Promiscuous, readTimeoutMilliseconds);
            device.StartCapture();


        }


            //Console.WriteLine();
            //Console.WriteLine("-- Listening on {0}, hit 'Enter' to stop...",
            //    device.Description);
                    /// <summary>
        /// Prints the time and length of each received packet
        /// </summary>
        /// 

        protected  void device_OnPacketArrival(object sender, CaptureEventArgs e)
        {
            DateTime time = e.Packet.PcapHeader.Date;
            uint len = e.Packet.PcapHeader.PacketLength;
            //Console.WriteLine("{0}:{1}:{2},{3} Len={4}", 
            //    time.Hour, time.Minute, time.Second, time.Millisecond, len);

           // Console.WriteLine(e.Packet.ToString());

            listViewPackets.Items.Add(e.Packet.ToString());


        }



        }


}

................................. .................................... here is the original code:

using System;
using System.Collections.Generic;
using SharpPcap;
namespace SharpPcap.Test.Example3
{
    /// <summary>
    /// Basic capture example
    /// </summary>
    public class BasicCap
    {
        public static void Main(string[] args)
        {
            // Print SharpPcap version
            string ver = SharpPcap.Version.VersionString;
            Console.WriteLine("SharpPcap {0}, Example3.BasicCap.cs", ver);

            // Retrieve the device list
            var devices = LivePcapDeviceList.Instance;

            // If no devices were found print an error
            if(devices.Count < 1)
            {
                Console.WriteLine("No devices were found on this machine");
                return;
            }

            Console.WriteLine();
            Console.WriteLine("The following devices are available on this machine:");
            Console.WriteLine("----------------------------------------------------");
            Console.WriteLine();

            int i = 0;

            // Print out the devices
            foreach(LivePcapDevice dev in devices)
            {
                /* Description */
                Console.WriteLine("{0}) {1} {2}", i, dev.Name, dev.Description);
                i++;
            }

            Console.WriteLine();
            Console.Write("-- Please choose a device to capture: ");
            i = int.Parse( Console.ReadLine() );

            LivePcapDevice device = devices[i];

            // Register our handler function to the 'packet arrival' event
            device.OnPacketArrival += 
                new PacketArrivalEventHandler( device_OnPacketArrival );

            // Open the device for capturing
            int readTimeoutMilliseconds = 1000;
            device.Open(DeviceMode.Promiscuous, readTimeoutMilliseconds);

            Console.WriteLine();
            Console.WriteLine("-- Listening on {0}, hit 'Enter' to stop...",
                device.Description);

            // Start the capturing process
            device.StartCapture();

            // Wait for 'Enter' from the user.
            Console.ReadLine();

            // Stop the capturing process
            device.StopCapture();

            Console.WriteLine("-- Capture stopped.");

            // Print out the device statistics
            Console.WriteLine(device.Statistics().ToString());

            // Close the pcap device
            device.Close();
        }

        /// <summary>
        /// Prints the time and length of each received packet
        /// </summary>
        private static void device_OnPacketArrival(object sender, CaptureEventArgs e)
        {
            DateTime time = e.Packet.PcapHeader.Date;
            uint len = e.Packet.PcapHeader.PacketLength;
            Console.WriteLine("{0}:{1}:{2},{3} Len={4}", 
                time.Hour, time.Minute, time.Second, time.Millisecond, len);
            Console.WriteLine(e.Packet.ToString());
        }
    }
}

Answer 1

When making a call to a control from another thread:

if (listView1.InvokeRequired)
{
    listView1.BeginInvoke(new MethodInvoker(
        () => /*whatever you want with listview */));
}
else
{
    /* whatever you want with listview */
}

If you know for sure that it will always be on another thread, then just forget the if/else and use the invoke.

EDIT:

so in your case, it'd look like:

if(listView1.InvokeRequired)
{
    listView1.BeginInvoke(new MethodInvoker(
        () => listViewPackets.Items.Add(e.Packet.ToString()) ));
}
else
{
    listViewPackets.Items.Add(e.Packet.ToString());
}

(again, or just the BeginInvoke call, if it will always run on a different thread)

EDIT 2 You'll notice that Shane uses Invoke and I use BeginInvoke. I use it as a force of habit. Using Invoke will block on the UI thread, and if you're performing an operation that takes longer, using BeginInvoke performs the update to the UI asynchronously.

Answer 2

You need to use Invoke because the packet is coming in on a different thread. UI controls cannot be modified on a thread other than the one they're created on. Invoke will execute the given delegate on the UI thread. For example, you could do this:

this.Invoke(new MethodInvoker(() => listViewPackets.Items.Add(e.Packet.ToString())), null);