Thread problem updating Windows Forms control in XNA C#

Question

I'm development a network card game, and for now i've two players connected but there is a problem with one of them, this one can't do anything on the game. Looks that screen was blocked. I'm think that is because a code i used before.

That code is:

if (InvokeRequired)
            {
                this.Invoke(new MethodInvoker(delegate
                {

                   ...

            }));
                return;
            }

The code above is surrounding code to changing Button values, make connection with server and create game window. Without this code a warning is shown.

InvalidOperationException was unhandled

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

Answer 1

Win Forms only allows the UI thread to access and create UI Controls. There is an inbuilt way to run delegates on the UI thread for particular control: Control.BeginInvoke(): http://msdn.microsoft.com/en-us/library/0b1bf3y3.aspx.

So you would need something like:

 if (BeginInvokeRequired)
 {
     startGameButton.BeginInvoke(new InvokeDelegate(delegate()
       {
          startGameButton.Text = "blah blah";
       }));
 }
 else
 {
     ...
 }

(If your code is in the startGameButton as it seems to be just replace startGameButton with this).

Incidentally there are few bad things with your original code. Notice I have removed your early return in the if block and I wrap the rest of the method in the else - this is because I am using BeginInvoke() not Invoke() which will return immediately - your delegate will be placed on a queue and be run when UI thread can run it - using Invoke you would have to wait until the UI thread has run it which is unneccesary (it should be run straight away anyway as the UI should not have long running operations to perform).

You needn't use anonymous delegates by the way:

public void UpdateStartButton()
{
    startGameButton.BeginInvoke(new InvokeDelegate(UpdateStartButtonCallback));
}

private void UpdateStartButtonCallback()
{
    startGameButton.Text = "blah blah";
}

Answer 2

Looks like you're using WinForms for your windows. You're not allowed to run WinForms control delegates on a thread that does not own said control.

The old way of working around this is described here: http://msdn.microsoft.com/en-us/library/zyzhdc6b(v=vs.80).aspx

Though instead I would take the new school route and use BeginInvoke: http://msdn.microsoft.com/en-us/library/0b1bf3y3(v=vs.80).aspx

Which just lets you forget about any of that boilerplate code :)