我正在使用Auth0Client for Windows Phone 8.0项目。我对Auth0.SDK.AuthenticationCancelException有问题，因为我在单击LoginFacebookTap按钮后一直按下后退按钮，它会使我的应用程序崩溃。

所以当我加载应用程序时，我会转到LoginView页面，有一个按钮会调用：

private async void LoginFacebookTap(object sender, System.Windows.Input.GestureEventArgs e)
{
    var result = await authorizationService.LoginAuth0(AuthorizationService.AuthorizationServiceType.Facebook, "", "");
    if (result == true)
    {
        MessageBox.Show("OK!");
    }
}

这是我的方法LoginAuth0

public async Task<Boolean> LoginAuth0(AuthorizationServiceType type, string email, string password)
{
    if (NetworkService.IsNetworkAvailable())
    {
        try
        {
            Auth0User user;
            switch (type)
            {
                case AuthorizationServiceType.EmailAndPassword:
                    user = await auth0.LoginAsync(Constants.login_with_password_Auth0, email, password);
                    break;
                case AuthorizationServiceType.Email:
                    user = await auth0.LoginAsync(Constants.login_azure_Auth0);
                    break;
                case AuthorizationServiceType.Facebook:
                    user = await auth0.LoginAsync(Constants.login_facebook_Auth0);
                    break;
                case AuthorizationServiceType.Google:
                    user = await auth0.LoginAsync(Constants.login_google_Auth0);
                    break;
                case AuthorizationServiceType.Linkedin:
                    user = await auth0.LoginAsync(Constants.login_linkedin_Auth0);
                    break;
                case AuthorizationServiceType.Twitter:
                    user = await auth0.LoginAsync(Constants.login_twitter_Auth0);
                    break;
                case AuthorizationServiceType.Windows:
                    user = await auth0.LoginAsync(Constants.login_windows_Auth0);
                    break;
            }
        }
        catch (AuthenticationCancelException)
        {
            System.Diagnostics.Debug.WriteLine("User press cancel on Authentication");
            return false;
        }
        catch (AuthenticationErrorException ex)
        {
            MessageBox.Show(Resources.AppResources.TitleError + " : " + ex.Message);
            return false;
        }
        catch (Exception exc)
        {
            MessageBox.Show(Resources.AppResources.MessageErrorUserNotExists);
            System.Diagnostics.Debug.WriteLine("Unknown exception: "+exc.Message);
            return false;
        }
        try
        {
            var targetClientId = Constants.clientId_Auth0;
            var options = new Dictionary<string, string>
            {
                { "scope", "openid profile" }
            };
            var delegationResult = await auth0.GetDelegationToken(targetClientId, options);
            if (delegationResult != null)
            {
                String jsonString = delegationResult["id_token"].ToString();
                System.Diagnostics.Debug.WriteLine("Application received token: " + jsonString);
                return true;
            }
            else MessageBox.Show(AppResources.MessageErrorSigning);
        }
        catch(Exception exc)
        {
            MessageBox.Show(Resources.AppResources.TitleError +" : " + exc.Message);
        }
        return false;
    }
    else
    {
        MessageBox.Show(Resources.AppResources.MessageErrorNoConnection);
        return false;
    }
}

在我点击LoginFacebookTap并按下Back按钮后，结果将是：

类型的第一次机会例外中发生"Auth0.SDK.AuthenticationCancelException"Auth0Client.Phone.Silverlight.ni.DLL类型的首次机会异常mscorlib.ni.dll中出现"Auth0.SDK.AuthenticationCancelException"类型的第一次机会例外mscorlib.ni.dll中出现"Auth0.SDK.AuthenticationCancelException"System.InvalidOperationException"类型的首次机会异常出现在Microsoft.Phone.ni.dll 中

然后应用程序崩溃，并显示"InvalidOperationException CanGoBack为false时无法返回。"。这是错误还是？

更新

我发现，只有当你登录到你的脸书账户并通过身份验证时，才会发生这种情况。然后，当你再次运行应用程序并点击LoginFacebookTap时，你不会被重定向到facebook登录页面，但你会自动重定向回认证的"OK"结果。在你被重定向回LoginView之前，你会看到白色屏幕，当你按下back时，你会返回"InvalidOperationException CanGoBack为false时无法返回"

更新2

我在Auth0.SDK:中的发现

/// <summary>
/// Handler for the browser control's navigation failed event.  We use this to detect errors
/// </summary>
private void BrowserControl_NavigationFailed(object sender, NavigationFailedEventArgs e)
{
    WebBrowserNavigationException navEx = e.Exception as WebBrowserNavigationException;
    if (navEx != null)
    {
        // Pass along the provided error information.
        responseErrorDetail = string.Format("Error code: {0}", navEx.StatusCode);
    }
    else
    {
        // No error information available.
        responseErrorDetail = NoDetailsAvailableMessage;
    }
    responseStatus = PhoneAuthenticationStatus.ErrorHttp;
    authenticationFinished = true;
    e.Handled = true;
    // Navigate back now.
    this.NavigateBackWithProgress();
}
/// <summary>
/// Displays the progress bar and navigates to the previous page.
/// </summary>
private void NavigateBackWithProgress()
{
    ShowProgressBar();
    NavigationService.GoBack();
}

在NavigationService.GoBack（）；当CanGoBack为false时，我们有InvalidOperationException无法返回。

private void NavigateBackWithProgress()
 {
     ShowProgressBar();
    if(NavigationService.CanGoBack)
        NavigationService.GoBack();
 }

private void NavigateBackWithProgress()
 {
     ShowProgressBar();
    if(this.Frame != null && this.Frame.CanGoBack)
        this.Frame.GoBack();
 }