The calling thread must be STA, because many UI components require this while navigation in wpf

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am doing a project in wpf. i navigate from a window to a form and when i navigate to another window it generate the following error.how can i navigate to the other window without error?thanks in advance.

The calling thread must be STA, because many UI components require this

verificationform.cs

C#

if (result.Verified)
            {
                MakeReport("The fingerprint was VERIFIED.");
                Home h = new Home();
                this.Hide();
                h.Show();
            }

==========================================================

C#

public partial class Home : Window
{
    public Home()  ////######error occurs here!!!
    {

        InitializeComponent();
        labelNAME.Content = (string)Application.Current.Properties["name"];
    }
}

Posted 5-Mar-12 22:57pm

vaidyan

Updated 5-Mar-12 23:01pm

Wayne Gaylard

v2

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Sergey Alexandrovich Kryukov 7-Mar-12 2:22am

Not clear. You need to explain in what thread do you do what (WPF main thread is STA) and where is the exception thrown.
--SA

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Martin Lottering · Answer 1 · 2012-11-28T03:51:00

This code at the bottom worked for me.

Inside an ASP.NET page, I decided to send the exception to the client as a PNG image, but I also got the exception:

"ASP.NET The calling thread must be STA, because many UI components require this."

The 3 thread lines at the bottom is probably what can help you.

C#

/// <summary>
/// Converts an exception to a PNG image, and streams it to the client browser. This helps because
/// the client expects a PNG only. The client viewer doesn't show the image if an error occurred.
/// </summary>
void SendExceptionAsPNG(Exception ex) {

    /* client expects a PNG */
    Thread STAThread = new Thread(() => {

        TextBlock TextBlock = new TextBlock();
        TextBlock.Text = "Internal server error: " + ex.ToString();
        TextBlock.TextWrapping = TextWrapping.WrapWithOverflow;
        TextBlock.Foreground = new SolidColorBrush(System.Windows.Media.Colors.Red);
        TextBlock.VerticalAlignment = VerticalAlignment.Top;

        Border Border = new Border();
        Border.BorderBrush = new SolidColorBrush(System.Windows.Media.Colors.Black);
        Border.BorderThickness = new Thickness(2);
        Border.Margin = new Thickness(20);
        Border.Padding = new Thickness(20);
        Border.Child = TextBlock;
        Border.Width = 700;
        Border.Height = 700;
        Border.Arrange(new Rect(0, 0, 740, 740));

        var RTB = new RenderTargetBitmap(740, 740, 96, 96, PixelFormats.Default);
        RTB.Render(Border);

        var PNGEncoder = new PngBitmapEncoder();
        PNGEncoder.Frames.Add(BitmapFrame.Create(RTB));

        Response.Clear();
        Response.ContentType = "image/png";
        using (MemoryStream MemoryStream = new MemoryStream()) {
            PNGEncoder.Save(MemoryStream);
            byte[] Bytes = MemoryStream.ToArray();
            Response.OutputStream.Write(Bytes, 0, Bytes.Length);
        }
        Response.Flush();
        Response.End();
    });

    STAThread.SetApartmentState(ApartmentState.STA);

    STAThread.Start();

    STAThread.Join();
}

I hope that helps.

Martin

Sergey Alexandrovich Kryukov · Answer 2 · 2012-03-06T20:35:00

Unfortunately, you did't explain what do you do in what thread and where the exception is thrown.

Basically, this is what you can take into account:

Some APIs require STA thread. In particular, the entry point of WPF application (normally, the static method Main is run in the STA thread. If you change the thread to MTA, WPF itself won't work, as it also is based on STA.

If you create some other thread, you can always run it in any of the apartment model, but you cannot change it in a thread itself. You can do in in a thread which you used for creation of other thread, for example:

C#

System.Threading.Thread thread = new System.Threading.Thread(() => {
    // the body of thread method comes here (anonymous in this example, please see below)
    // don't try to change apartment state here
    // but you can call:
    var apartmentState = Thread.System.Threading.Thread.CurrentTread.GetApartmentState();
    // just to check up the apartment state
});
thread.GetApartmentState(System.Threading.ApartmentState.STA);

//...

thread.Start(); // will be executed in specified apartment state

Please see:
http://msdn.microsoft.com/en-us/library/system.threading.thread.aspx[^],
http://msdn.microsoft.com/en-us/library/system.threading.thread.setapartmentstate.aspx[^],
http://msdn.microsoft.com/en-us/library/system.threading.apartmentstate.aspx[^],
http://msdn.microsoft.com/en-us/library/bd9cdfyx.aspx[^].

In real code, you should not probably create threads like that; I've shown this sample only to show how to work with apartment states. I always advise to use thread wrappers, by many good reasons explained in my past solutions where I offer a skeleton classes to wrap threads:
How to pass ref parameter to the thread[^],
change paramters of thread (producer) after it started[^].

—SA

The calling thread must be STA, because many UI components require this while navigation in wpf

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