Cross-thread operation not valid

Question

Hi All,

I keep getting the following error when debugging.

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

Here's the code that it points to:

    public  void OnDataReceived(IAsyncResult asyn)
    {
        try
        {
            SocketPacket socketData = (SocketPacket)asyn.AsyncState ;

            int iRx  = 0 ;
            // Complete the BeginReceive() asynchronous call by EndReceive() method
            // which will return the number of characters written to the stream 
            // by the client
            iRx = socketData.m_currentSocket.EndReceive (asyn);
            char[] chars = new char[iRx +  1];
            System.Text.Decoder d = System.Text.Encoding.UTF8.GetDecoder();
            int charLen = d.GetChars(socketData.dataBuffer, 
                                     0, iRx, chars, 0);
            System.String szData = new System.String(chars);
            richTextBoxReceivedMsg.AppendText(szData);

            // Continue the waiting for data on the Socket
            WaitForData( socketData.m_currentSocket );
        }
        catch (ObjectDisposedException )
        {
            System.Diagnostics.Debugger.Log(0,"1","\nOnDataReceived: Socket has been closed\n");
        }
        catch(SocketException se)
        {
            MessageBox.Show (se.Message );
        }
    }

Can somebody please help me fix this? I appreciate any help at all

Thank you

Answer 1

You need to replace this:

richTextBoxReceivedMsg.AppendText(szData);

with something like

Invoke(new Action(() => richTextBoxReceivedMsg.AppendText(szData)));

The reason is that Windows Forms is not really designed to work across different threads. Invoke method will run the delegate you pass to it in the UI thread. If you want to manipulate UI elements via other threads, you'll have to run the actual manipulation on the UI thread. InvokeRequired property will tell you when you need to use Invoke rather than calling the method directly.

Answer 2

Check out Jon Skeet's article on multi-threading, particularly the page on multi-threading winforms. It should fix you right up.

Answer 3

This link may be able to help you.

Answer 4

check by writing the given statement in your form1() constructor RichTextBox.CheckForIllegalCrossThreadCalls = false;

Thank u....