New to threading, trouble with delegates

Hi. I'm working on a chat program, and I'm having some trouble with the thread that is supposed to get text from a file and append it to a rich text box that acts as the chat display. The problem arises when I attempt to edit the textbox text from the thread, I get this error:

Code:

Control 'richTextBox1' accessed from a thread other than the thread it was created on.

Here is the thread's function:

Code:

private void Thread_get_text()
        {
            string text = "";
            string new_text = "";

            while (true)
            {
                StreamReader read = new StreamReader("chat.log");
                new_text = read.ReadLine();
                if (text != new_text)
                {
                    text = new_text;
                    read.Close();
                    richTextBox1.Text = text;
                }
                read.Close();
                Thread.Sleep(10);
            }
        }

Now, I understand that I'm supposed to use a delegate here, but I don't quite understand how to use one. I looked at MSDN's delegate tutorial and followed their example, and I ended up with this:

Code:

//declaration
private delegate void Del(string text);

//AppendText definition
private void AppendText(string text)
{
      richTextBox1.Text = text;
}

private void Thread_get_text()
        {
            Del handler = AppendText;
            string text = "";
            string new_text = "";

            while (true)
            {
                StreamReader read = new StreamReader("chat.log");
                new_text = read.ReadLine();
                if (text != new_text)
                {
                    text = new_text;
                    read.Close();
                    handler(text);
                }
                read.Close();
                Thread.Sleep(10);
            }
        }

This prompts the same error message: Control 'richTextBox1' accessed from a thread other than the thread it was created on.

What did I do wrong with the delegate? Is this even the correct approach to fixing my problem?

You need to Invoke when you are on a different thread than the main UI thread.

http://msdn.microsoft.com/en-us/libr...ol.invoke.aspx

or

http://msdn.microsoft.com/en-us/libr...gininvoke.aspx

As prog-bman says, you can't cross thread a GUI control. 2 useful functions are:

Code:

rtb.Invoke()
rtb.BeginInvoke()

Lots of demos on google and msdn.

Awesome. Thanks for the quick responses, guys. I'll check it out.

Note that you might want to put a try/catch block around the Invoke method since in some cases (like when you are terminating threads when the main windows closes) they will throw an exception. Just an empty try/catch will do the trick