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!!

score 14 · Accepted Answer · answered Jan 31 '13 at 15:35

14

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.

answered Jan 31 '13 at 15:35

Federico Berasategui

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never would have found that mistake.. even my programming teacher hasnt found it.. Thank you very much :-) – Maaaario Jan 31 '13 at 15:49
OMG you have a programming teacher and he's teaching you WPF? lucky you!! – Federico Berasategui Jan 31 '13 at 15:52
Yes we have :-) he also teached us some game programming in c++ but mostly we're doing wpf :) – Maaaario Jan 31 '13 at 16:13
@Bobb no I wasn't being sarcastic. WPF is the the single most enjoyable framework. Working with it is pleasant and straightforward, versus the multiple HACKS you need to do almost anything useful in say winforms. Not to mention other things outside he .Net world, such as java, that doesn't even have real generics, delegates, or LinQ. – Federico Berasategui Feb 01 '13 at 00:09

Thread must be STA-Thread, but it already is

1 Answers1