Cross-thread operation not valid

Question

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","
OnDataReceived: S…

Accepted Answer

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.

Cross-thread operation not valid

Solution

Problem