UnauthorizedAccessException: Invalid cross-thread access in Silverlight application (XAML/C#)

Question

Relatively new to C# and wanted to try playing around with some third party web service API\'s with it.

Here is the XAML code

Answer 1

A useful way to get easy cross thread access with the CheckAccess call is to wrap up a utility method in a static class - e.g.

public static class UIThread
{
    private static readonly Dispatcher Dispatcher;

    static UIThread()
    {
        // Store a reference to the current Dispatcher once per application
        Dispatcher = Deployment.Current.Dispatcher;
    }

    /// 

    ///   Invokes the given action on the UI thread - if the current thread is the UI thread this will just invoke the action directly on
    ///   the current thread so it can be safely called without the calling method being aware of which thread it is on.
    /// 
    public static void Invoke(Action action)
    {
        if (Dispatcher.CheckAccess())
            action.Invoke();
        else
            Dispatcher.BeginInvoke(action);
    }
}

then you can wrap any calls that update the UI where you may be on a background thread like so:

private void twitterCallback(IAsyncResult result)   
{   
        HttpWebRequest request = (HttpWebRequest)result.AsyncState;   
        HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(result);   
        TextReader reader = new StreamReader(response.GetResponseStream());   
        string strResponse = reader.ReadToEnd();   

        UIThread.Invoke(() => TwitterPost.Text = "hello there");
}   

This way you don't have to know whether you are on a background thread or not and it avoids the overhead of adding methods to every control to check this.