Cross thread operation not valid

im trying to access a rich textbox on another form im using the following code to do so:

Private Delegate Sub StringDelegateChat(text As String, window As ChatWindow)
    Private Sub AppendTextChatWindows(text As String, window As ChatWindow)
        Try              
            If window.RichTextBox1.InvokeRequired Then
                window.Invoke(New StringDelegateChat(AddressOf AppendTextChatWindows), text, window)
            Else
                window.RichTextBox1.AppendText(text)
                window.RichTextBox1.SelectionStart = window.RichTextBox1.Text.Length
                window.RichTextBox1.ScrollToCaret()
            End If
        Catch ex As Exception
            MessageBox.Show(ex.ToString)
        End Try
    End Sub

but i get the cross th开发者_如何转开发read operation not valid error, i think it does this because it misses out the window.invoke part of the if statement. i also tried replacing theIf window.RichTextBox1.InvokeRequired Then to If InvokeRequired Then but it gets caught in a continues loop and a stack overflow error is thrown.

Thanks Houlahan

I believe, on line 5, window.Invoke should be changed to window.RichTextBox1.Invoke.

Private Delegate Sub StringDelegateChat(text As String, window As ChatWindow)
Private Sub AppendTextChatWindows(text As String, window As ChatWindow)
    Try
        If window.RichTextBox1.InvokeRequired Then
            window.RichTextBox1.Invoke(New StringDelegateChat(AddressOf AppendTextChatWindows), text, window)
        Else
            window.RichTextBox1.AppendText(text)
            window.RichTextBox1.SelectionStart = window.RichTextBox1.Text.Length
            window.RichTextBox1.ScrollToCaret()
        End If
    Catch ex As Exception
        MessageBox.Show(ex.ToString)
    End Try
End Sub

Have you tried:

    Private Sub AppendTextChatWindows(text As String, window As ChatWindow)
        Try              
            If window.RichTextBox1.InvokeRequired Then
                window.RichTextBox1.BeginInvoke(New StringDelegateChat(AddressOf AppendTextChatWindows), text, window)
                Exit Sub 
            Else
                window.RichTextBox1.AppendText(text)
                window.RichTextBox1.SelectionStart = window.RichTextBox1.Text.Length
                window.RichTextBox1.ScrollToCaret()
            End If
        Catch ex As Exception
            MessageBox.Show(ex.ToString)
        End Try
    End Sub

Basically, I am asking about BeginInvoke rather than Invoke. Although I would expect, as another poster mentioned, that you should be using the same thing you check the required against to invoke. (ie both window.invokeRequired & window.BeginInvoke or the control)

I cant see any errors in your code. You might want to check for any events that are fired when updating the RichTextbox. They might be causing a cross threading.

As a workaround to your problem, working with objects, you are less likely o encounter cross threading problems.