Question

I have a windows mobile application written in C# that has more dialogs. I want to update a dialog, when an event is triggered. Here is the code:

 public void ServerStateChanged()
        {
            // update the interface
            try
            {
                if (this.Focused)
                {
                    this.noConnectionsLL.Text = this.tcpServer.ClientsCount.ToString();
                }
            }
            catch (Exception exc)
            {
            }
        }

The code works a few times, but then I get this System.NotSupportedException with this stacktrace: at Microsoft.AGL.Common.MISC.HandleAr()\r\nat System.Windows.Forms.Control.get_Focused()\r\nat DialTester.Communication.TCPServerView.ServerStateChanged()\r\nat ...

Does it matter from which thread is triggered the event? because I can’t figure out what the problem is, why it works a few times and then it crashes.

Answer 1

It’s likely to be a cross-thread issue. Checking this.InvokeRequired at the top of the function and reacting accordingly would definitely improve the safety of the function. Something like this:

public void ServerStateChanged()         
{
    if(this.InvokeRequired)
    {
        this.Invoke(new delegate
        {
            ServerStateChanged();
        }
        return;
    }

    if (this.Focused)                 
    {                     
        this.noConnectionsLL.Text = this.tcpServer.ClientsCount.ToString();
    }             
}