脸书登录未实现异常错误

im 使Facebook登录到我的窗口手机8.1 . 当单击登录按钮时，它会破坏应用程序年龄我这个

类型为"System.NotImplementException"的异常发生在 mypriject.exe但没有在用户代码中处理

其他信息：未实现

如果存在此异常的处理程序，则程序可能是安全的 继续。

然后带我去这个app.g.i.cs 页面并突出显示此行

#if DEBUG && !DISABLE_XAML_GENERATED_BREAK_ON_UNHANDLED_EXCEPTION
            UnhandledException += (sender, e) =>
            {
                if (global::System.Diagnostics.Debugger.IsAttached) global::System.Diagnostics.Debugger.Break();
            };

**

这是我的代码请帮助我**

    public sealed partial class BlankPage1 : Page
{
    FacebookClient fb = new FacebookClient();
    string AccessToken = null;
    public BlankPage1()
    {
        this.InitializeComponent();
    }
    /// <summary>
    /// Invoked when this page is about to be displayed in a Frame.
    /// </summary>
    /// <param name="e">Event data that describes how this page was reached.
    /// This parameter is typically used to configure the page.</param>
    private async void Button_Click(object sender, RoutedEventArgs e)
    {
        string redirect_url="https://www.facebook.com/connect/login_seccess.html";
        var loginURL = fb.GetLoginUrl(new{
            client_id ="**myapp id here**",
            redirect_uri = redirect_url,
            response_type ="token",
            scope ="email,publish_stream,user_groups"

        });
          var res= await WebAuthenticationBroker.AuthenticateAsync(WebAuthenticationOptions.None,loginURL,new Uri(redirect_url)  );
        if(res.ResponseStatus==WebAuthenticationStatus.Success)
        {
            var callback = new Uri(res.ResponseData.ToString());
            var token = fb.ParseOAuthCallbackUrl(callback);
            AccessToken = token.AccessToken;
            await new MessageDialog("AccessToken").ShowAsync();
        }
    }
}