Cross-thread operation not valid while listening to a COM port [duplicate]

Answer 1

You can also do the following whenever accessing a UI control from a different thread than the one it was created on:

(.NET 3.5)

myControl.BeginInvoke(new MethodInvoker( () => myControl.whatever = whatever; ));

or (.NET 2.0)

myControl.BeginInvoke(new MethodInvoker( delegate { myControl.whatever = whatever; ));

edit> Sometimes using Invoke for a long running operation can/will still hang the ui, using BeginInvoke obviously performs that operation asynchronously, and the ui will not hang.

Answer 2

My guess is that MyDataReceivedHandler is running on a different thread than the GUI. In order to fix that, you need to invoke the Text setters on the correct thread. This is a sample of doing so:

public void SetControlText(Control control, string text)
{
    if (this.InvokeRequired)
    {
        this.Invoke(new Action<Control,string>(SetControlText), new object[] { control, text });
    }
    else
    {
        control.Text = text;
    }
}

private void MyDataReceivedHandler(object sender, SerialDataReceivedEventArgs e)
{
    try
    {
        //sp.PortName = "COM3";
        //sp.Open();
        SetControlText(Label1, sp.ReadLine());
    }
    catch (Exception exception)
    {
        SetControlText(RichTextBox1, exception.Message + "\n\n" + exception.Data);
    }
    finally
    {
        sp.Close();
    }
}

If you are using .NET Framework 2.0, the above Action<T1, T2> delegate is not available, so you will have to define your own one:

private delegate void SetControlTextHandler(Control control, string text);

public void SetControlText(Control control, string text)
{
    if (this.InvokeRequired)
    {
        this.Invoke(new SetControlTextHandler(SetControlText), new object[] { control, text });
    }
    else
    {
        control.Text = text;
    }
}

The SetControlText method can be made shorter (and even static) like this (this works in both 2.0 and 3.5):

public static void SetControlText(Control control, string text)
{
    ´control.Invoke((MethodInvoker)delegate { control.Text = text; });
}

Then you don't need to do the check of InvokeRequired each time, but you will on the other hand wrap the call in a delegate even if it is not needed. I think that in a GUI method like this any performance difference between those two is neglectible so I tend to use the shorter form, simply because it is less code to write.