Thread must be STA-Thread, but it already is

Question

Im working on my thesis about an C# WPF program, but i ran into an error i dont understand.

Somewhere in my MainWindow Code im starting a new Thread like this:

Thread searchServer = new Thread(new ThreadStart(doSearchServer));
            searchServer.SetApartmentState(ApartmentState.STA);
            searchServer.Start();

The doSearchServer methods does the following:

    private void doSearchServer()
    {
        bool connected = ServerConnection.authentication();
        ServerConnection.getDeviceList();
        gotDataFromServer = connected;

        if (connected)
          ..
          ..
    }

The ServerConnection class is static because i also need that class in some other Windows.

At ServerConnection.authentication() the client (my Program) tries to authenticate on my server. If a password is required, i wanted to open a new PasswordWindow as you can see here:

public static bool authentication()
    {
        UdpClient client = new UdpClient();
        IPEndPoint ip = new IPEndPoint(IPAddress.Broadcast, 55042);
        IPEndPoint ipRec = new IPEndPoint(IPAddress.Any, 0);

        byte[] bytes = Encoding.UTF8.GetBytes("authent|Username|Windows");
        client.Send(bytes, bytes.Length, ip);

        //Receive Answer
        byte[] recBuffer = client.Receive(ref ipRec);
        string recString = Encoding.UTF8.GetString(recBuffer);

        if (recString.Equals("authent|password"))
        {
            //Send Passwort
            Console.WriteLine("Password Required");

            Dispatcher.CurrentDispatcher.Invoke(new Action(() =>
            {
            PasswordWindow pw = new PasswordWindow();
            pw.ShowDialog();
            if (pw.ShowDialog() == true)
            {
                //send PW
            }
            else
            {
                //Dont send PW
            }
            }));

            client.Send(bytes, bytes.Length, ip);
            .
            .
            .
        }

At the PasswordWindow Contructor it crashes. I tried STA + Dispatcher, MTA + Dispatcher, STA only.. anything i tried didnt work... i really dont get it.

Can someone please explain me why it still says that the Thread needs to be an STA Thread?

Thanks for any kind of help!!

Federico Berasategui Federico Berasategui · Accepted Answer · 2013-01-31T15:35:39

change Dispatcher.CurrentDispatcher

to

System.Windows.Application.Current.Dispatcher

because when accessing the Dispatcher.CurrentDispatcher property from a thread that is not the "UI Thread" (the one associated with the Dispatcher that started the application in the first place), a new Dispatcher is created, which is not what you need here.

Thread must be STA-Thread, but it already is

1 Answers