c# System.InvalidOperationException

Question

General

I'm trying to write a very simple TCPIP client server in C# to connect to an IP Address, with a port number, and ask quite simple line commands, and then place the replies in a Gridbox, graph or other display option.

I have looked online and found a down loadable utility that does just this, written by Jayan Nair, and this appears to send the message correctly, and receive the reply ok.

The problem comes when I try and load the reply data into a richtext or GridView.

The error message I'm getting is :- System.InvalidOperationException

I have asked Microsoft Forums, and they have given me a very complicated, ambiguous and overly involved indication as to what I should do, and this involves something called INVOKE and BeginInvoke, and they whole things seems to be a project in it;s own right.

What I'm after is just an example that works, without being too complicated.

Here's the code :-

        try
        {
            SocketPacket theSockId = (SocketPacket)asyn.AsyncState;
            int iRx = theSockId.thisSocket.EndReceive(asyn);
            char[] chars = new char[iRx + 1];
            System.Text.Decoder d = System.Text.Encoding.UTF8.GetDecoder();
            int charLen = d.GetChars(theSockId.dataBuffer, 0, iRx, chars, 0);
            // 
            System.String szData = new System.String(chars);
            richTextRxMessage.Text =  szData;  // fails
            //textBox1.Text = szData;          // also fails
            WaitForData();
        }

and here's the error message :-

base {System.Windows.Forms.TextBoxBase} = {Text = '((System.Windows.Forms.RichTextBox)    (((System.Windows.Forms.RichTextBox)(richTextRxMessage)))).Text' threw an exception of type   'System.InvalidOperationException'}

Additional information is :- szData contains about 6300 characters, including tabs (9) and returns (13), and is consistant with the message sent from the server I've also tried it with using a textbox instead of richtext, same result

For those interested

Here's the Microsoft link

http://social.msdn.microsoft.com/Forums/en-US/csharpgeneral/thread/12a67fb0-847e-4e2b-baa8-ef6ceed60aa4/

---

Solution 1

The InvalidOperationException that you receive will likely have the inner exception "The calling thread cannot access this object because a different thread owns it".

For the sake of debugging you can quickly set CheckForIllegalCrossThreadCalls to false. This will stop the run-time from throwing you an exception, however just because you're not receiving the exceptions does not mean that they are not happening so this is a bad practice for distributed software but very handy for debugging.

In order to resolve your issue you need to invoke the code that interacts with the RichTextBox on the UI Thread aka the thread the control was created on and the only thread that is allowed to run code that interacts with the control.

To invoke the code on the UI Thread you can use the following, succinct statement:

richTextRxMessage.BeginInvoke(new MethodInvoker(() => richTextRxMessage.Text = szData));

Very simply, all you are doing here is passing the statement you wish to invoke on the UI Thread by means of a delegate.

Solution 2

Here's a function I use in some of my stuff;

public static void InvokeEx<T>(this T @this, Action<T> action) where T : ISynchronizeInvoke
{
    if (@this.InvokeRequired)
    {
        @this.Invoke(action, new object[] { @this });
    }
    else
    {
        action(@this);
    }
}

It's pretty much a nice little method for dealing with any sort of invoke, and cuts down the lines of code when you're using it. To use it, simply use this;

Control.InvokeEx(f => control.DoStuff());

So for example, you might use;

richTextRxMessage.InvokeEx(f => richTextRxMessage.Text =  szData);

Edit: As others have said, this error is more than likely due to accessing a control on a thread other than the one it was created on, which is why the invokes are required.