Question

I’m trying to make a message box modal but I’m running into threading issues.

I have a class like this:

public static class DisplayMessage()
{
    public static void ErrorMessage(string errorMessage)
    {
         MessageBox.Show(errorMessage, "Error", MessageBoxButtons.OK,MessageBoxIcon.Error);
    }
    //other similar methods
}

So I want the message box to be modal to the main form. MessageBox.Show is overloaded so that you can specify an IWin32Window. So I tried using .ActiveForm but I get this:

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

Answer 1

Try this:

    public static void ErrorMessage( Form Parent, string errorMessage )
    {
        if ( Parent != null && Parent.InvokeRequired )
            Parent.Invoke( (Action)(() => MessageBox.Show( errorMessage, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error )) );
        else
            MessageBox.Show( errorMessage, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error );
    }