How can I safely raise events in an AsyncCallback?

Question

I'm writing a wrapper class around a TcpClient which raises an event when data arrives. I'm using BeginRead and EndRead, but when the parent form handles the event, it's not running on the UI thread. I do I need to use delegates and pass the context into the callback? I thought that callbacks were a way to avoid this...

void ReadCallback(IAsyncResult ar)
{
    int length = _tcpClient.GetStream().EndRead(ar);
    _stringBuilder.Append(ByteArrayToString(_buffer, length));
    BeginRead();
    OnStringArrival(EventArgs.Empty);
}

Answer 1

The parent form should be using the Invoke method on its controls in the event handler to ensure it's on the right thread; it's not the job of your background process to conform to what the UI needs. This msdn page has an example.