NavigationService.GoBack() unauthorized expcetion - windows-phone-7

Question

void CallBackVerifiedResponse(OAuthAccessToken at, TwitterResponse response)
{
if (at != null)
{
SerializeHelper.SaveSetting<TwitterAccess>("TwitterAccess", new TwitterAccess
{
AccessToken = at.Token,
AccessTokenSecret = at.TokenSecret,
ScreenName = at.ScreenName,
UserId = at.UserId.ToString()
});
}
}
private void ok_Click_1(object sender, EventArgs e)
{
if (String.IsNullOrEmpty(pinText.Text))
MessageBox.Show("Please enter PIN");
else
{
try
{
var cb = new Action<OAuthAccessToken, TwitterResponse>(CallBackVerifiedResponse);
service.GetAccessToken(_requestToken, pinText.Text, CallBackVerifiedResponse);
}
catch
{
MessageBox.Show("Something is wrong with the PIN. Try again please.", "Error", MessageBoxButton.OK);
}
}
}
My problem in is here when I use NavigationService.GoBack() inside the CallBackVerifiedResponse method i'm getting unauthorized access exception, and if i use it inside of the click event, I CallBackVerifiedResponse is not triggered. Any ideas?

Answer 1

It's been solved by using UIThread
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;
}
/// <summary>
/// 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.
/// </summary>
public static void Invoke(Action action)
{
if (Dispatcher.CheckAccess())
action.Invoke();
else
Dispatcher.BeginInvoke(action);
}
}
After this static class
I have called it inside of
CallBackVerifiedResponse
like this
UIThread.Invoke(()=>NavigationService.GoBack());

Answer 2

You can use Dispatcher.BeginInvoke to access the UIThread
Dispatcher.BeginInvoke(() =>
{
NavigationService.GoBack();
});

Answer 3

Or you could use your own smart dispatcher, used like this:
SmartDispatcher.BeginInvoke(() =>
{
MissionAccomplished();
});
Coded something as the following:
{
using System.ComponentModel;
using System.Windows.Threading;
using System.Windows;
using System;
public static class SmartDispatcher
{
/// <summary>
/// A single Dispatcher instance to marshall actions to the user
/// interface thread.
/// </summary>
private static Dispatcher _instance;
/// <summary>
/// Backing field for a value indicating whether this is a design-time
/// environment.
/// </summary>
private static bool? _designer;
/// <summary>
/// Requires an instance and attempts to find a Dispatcher if one has
/// not yet been set.
/// </summary>
private static void RequireInstance()
{
if (_designer == null)
{
_designer = DesignerProperties.IsInDesignTool;
}
// Design-time is more of a no-op, won't be able to resolve the
// dispatcher if it isn't already set in these situations.
if (_designer == true)
{
return;
}
// Attempt to use the RootVisual of the plugin to retrieve a
// dispatcher instance. This call will only succeed if the current
// thread is the UI thread.
try
{
_instance = Application.Current.RootVisual.Dispatcher;
}
catch (Exception e)
{
throw new InvalidOperationException("The first time SmartDispatcher is used must be from a user interface thread. Consider having the application call Initialize, with or without an instance.", e);
}
if (_instance == null)
{
throw new InvalidOperationException("Unable to find a suitable Dispatcher instance.");
}
}
/// <summary>
/// Initializes the SmartDispatcher system, attempting to use the
/// RootVisual of the plugin to retrieve a Dispatcher instance.
/// </summary>
public static void Initialize()
{
if (_instance == null)
{
RequireInstance();
}
}
/// <summary>
/// Initializes the SmartDispatcher system with the dispatcher
/// instance.
/// </summary>
/// <param name="dispatcher">The dispatcher instance.</param>
public static void Initialize(Dispatcher dispatcher)
{
if (dispatcher == null)
{
throw new ArgumentNullException("dispatcher");
}
_instance = dispatcher;
if (_designer == null)
{
_designer = DesignerProperties.IsInDesignTool;
}
}
/// <summary>
///
/// </summary>
/// <returns></returns>
public static bool CheckAccess()
{
if (_instance == null)
{
RequireInstance();
}
return _instance.CheckAccess();
}
/// <summary>
/// Executes the specified delegate asynchronously on the user interface
/// thread. If the current thread is the user interface thread, the
/// dispatcher if not used and the operation happens immediately.
/// </summary>
/// <param name="a">A delegate to a method that takes no arguments and
/// does not return a value, which is either pushed onto the Dispatcher
/// event queue or immediately run, depending on the current thread.</param>
public static void BeginInvoke(Action a)
{
if (_instance == null)
{
RequireInstance();
}
// If the current thread is the user interface thread, skip the
// dispatcher and directly invoke the Action.
if (_instance.CheckAccess() || _designer == true)
{
a();
}
else
{
_instance.BeginInvoke(a);
}
}
}
}