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Editorial Team
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Asked: 2026-05-28T07:27:03+00:00

I have a program which monitors a TCP connection for any data and fires

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I have a program which monitors a TCP connection for any data and fires an event when an entire message has been recieved. The listener is on a different thread from the UI Thread. When the event is fired, if the message requires any UI changes, I invoke the Form with the current change. If this invoke is ever hit, the function in the listener that triggered off the Event flags up a Cross-Thread operation not valid error. I dont understand why the thread that called the event would flag up that error when i am trying to avoid that error by invoking. Example:

Without the Invoke on the command:

if (cmd == "NEWID")
{
    usr = new User(usr.Name, int.Parse(NW_Connector.GetWord(msg, 1)));
    this.Text = "Note It - " + usr.Name + "(" + usr.ID + ")"; //Cross-Thread Here
}

Cross-Thread is flagged on the this.Text change.

When i add the Invoke:

if (cmd == "NEWID")
{
    usr = new User(usr.Name, int.Parse(NW_Connector.GetWord(msg, 1)));
    this.Invoke(new MethodInvoker(delegate { this.Text = "Note It - " + usr.Name + "(" + usr.ID + ")"; }));
}

The Cross-Thread is flagged on the function that fired the event:

if (NewMessage != null && NetworkConnectionState != ConnectionState.Closing)
    NewMessage(this, cl, data); //Cross-Thread Here

The NewMessage function is the event that is registered to:

    public delegate void RecievedMessage(object sender, Client messageSender, byte[] message);
    public event RecievedMessage NewMessage;

I dont understand why the Cross-thread is “moved” when invoking to the correct thread. Any help would be Fantastic!

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1 Answer

  1. Editorial Team

    I have absolutely no idea why, but doing a complete rebuild (rebuilding every project in the solution) Rectified the issue. The issue must then have been because the source code of the project i was changing was different from the operating programs source it was showing the Cross-Thread error at the closest possible valid source code avaliable on the stack trace.

    Strange i was not alerted that the source code was different But it has however fixed the issue. I hope this will help someone else with the same issue. It really freaked me out WHY the Cross-Thread issue would appear to be “falling back” to a previous location in the stack trace.

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