C# cross-thread call problem

Question

I'm writing a form app in c# and I need to be able to change the contents of a Rich Text Box from any thread, I tried using a delegate and InvokeRequired, but the delegate I made still gives me a cross-thread call error, and InvokeRequired crashes the form, without giving an error. Function I need to be able to execute from any thread:

    public static void updateSub(int what)
    {
        subDisplay.subBox.Text = tb[what];
    }

The delegate I tried to use:

    public delegate void UpdateDelegateVoid(int what);
    static public UpdateDelegateVoid uSub = new UpdateDelegateVoid(updateSub);
    uSub(0);

My InvokeRequired code:

    public static void updateSub(int what)
    {
        if (subDisplay.subBox.InvokeRequired)
        {
            subDisplay.subBox.Invoke(new MethodInvoker(finish));
        }
        else
        {
            subDisplay.subBox.Text = tb[what];
        }
    }

I'm not really sure why the code above isn't working. Thanks!

Answer 1

Strictly speaking, when you check InvokeRequired and find it's true, you should marshall the call to the same method. I'm not sure it fixes your specific problem (I'd need to see more exception details and code) but this is what I mean:

public static void updateSub(int what)
{
    if (subDisplay.subBox.InvokeRequired)
    {
        subDisplay.subBox.Invoke(new Action<int>(updateSub), what);
    }
    else
    {
        subDisplay.subBox.Text = tb[what];
    }
}

If you're getting "weird behaviour", then check that the form is actually created on the main application thread. In WinForms this isn't forced (as it is in WPF) so it's just possible that the thread that the form was created on isn't actually the root thread of the app.

Answer 2

Try this - where you call the same method if an invoke is required.

public void UpdateSub(string message)
{
    if (!subDisplay.subBox.InvokeRequired)
    {
        subDisplay.subBox.Text = message;
    }
    else
    {
        var d = new UpdateFormText(UpdateSub);
        Invoke(d, new object[] { message });
    }
}

Where UpdateFormText is the delegate

public delegate void UpdateFormText(string message);

Answer 3

I mostly use this, and it works perfectly. For the exact same purpose are what you are intending.

public void UpdateSub(string message)
{
    subDisplay.subBox.Invoke((Action)delegate {
        subDisplay.subBox.Text = message;
    });
}

Hope it help's your or someone else with it!