Setting a WPF button to visible within an IConnectionPoint event handler

Question

I'm fairly new to C# and WPF programing and right now this problem is giving me headaches.

What the program should do: The program displays a welcome screen with a text box, where a customer can enter his name. If the device comes near a Wireless Lan Access Points and connects successfully, a "Start" button on this main window should become visible.

What's not working: Setting the button visibility inside the event handler. The new style does not get applied. Furthermore, if I try to call any other code after setting the visibility attribute/property(?) it won't run (if I put a MessageBox.Show right before setting the visib. it will be shown, if I put it after setting the property, this code won't even be reached any more).

The code:

This is the button Element:

<Button Height="72" HorizontalAlignment="Center" Margin="319,507,315,0"
        Name="buttonStart" VerticalAlignment="Top" Width="168" FontSize="32"
        Content="Los geht's" Click="buttonStart_Click" />

This is the event handler registration within the MainWindow.xaml.cs

public partial class MainWindow : Window, INetworkListManagerEvents
{
    private INetworkListManager nlm_;
    private IConnectionPoint nlmICP_;
    private int nlmCookie_ = 0;

    private void InitNetManager()
    {
        nlm_ = new NetworkListManager();
        IConnectionPointContainer icpc = (IConnectionPointContainer)nlm_;
        Guid tempGuide = typeof(INetworkListManagerEvents).GUID;
        icpc.FindConnectionPoint(ref tempGuide, out nlmICP_);
        nlmICP_.Advise(this, out nlmCookie_);
    }

And finally, the event handler:

    public void ConnectivityChanged(NLM_CONNECTIVITY newConnectivity)
    {
        if (newConnectivity == NLM_CONNECTIVITY.NLM_CONNECTIVITY_DISCONNECTED ||
            ((int)newConnectivity & (int)NLM_CONNECTIVITY.NLM_CONNECTIVITY_IPV4_NOTRAFFIC) != 0)
        {
            MessageBox.Show("Disconnected"); // this will code is reached
            buttonStart.Visibility = Visibility.Hidden; // this is not getting applied
            MessageBox.Show("Disconnected");  // this will code is not reached (stepped with debugger)
        }

        if ((((int)newConnectivity & (int)NLM_CONNECTIVITY.NLM_CONNECTIVITY_IPV4_LOCALNETWORK) != 0) ||
            (((int)newConnectivity & (int)NLM_CONNECTIVITY.NLM_CONNECTIVITY_IPV4_INTERNET) != 0))
        {
            MessageBox.Show("Connected"); // see comments above
            buttonStart.Visibility = Visibility.Visible;
        }
    }

That's it - I hope you can help me.

Thank you very much in advance for your efforts!

Answer 1

Hum - now I feel bad for answering my own question, but my urge to solve this problem kept me googling and finally I found out, that I can only change my WPF elements from the UI thread, but the INetwork-Events are called within a different thread.

So I solved it this way:

    public void ConnectivityChanged(NLM_CONNECTIVITY newConnectivity)
    {
        if (newConnectivity == NLM_CONNECTIVITY.NLM_CONNECTIVITY_DISCONNECTED ||
            ((int)newConnectivity & (int)NLM_CONNECTIVITY.NLM_CONNECTIVITY_IPV4_NOTRAFFIC) != 0)
        {
            Dispatcher.BeginInvoke(DispatcherPriority.Normal, new Action(
                delegate()
                {
                    buttonStart.Visibility = Visibility.Hidden;
                }
            ));
        }
        // ...
    }

Thanks for your time though :)

Answer 2

Not a direct answer to your question (because it's already answered) but the WPF way to do things would be to to have a property CanConnect you bind the visibility to (with the bool to visibility converter).

Whenever you touch a UI control in your code then it's a very good indicator that your design needs improvement.