// Add some word here to spesify it's a singelton ?
 public static AppConfigService GetInstance()
 {
     if (AppConf == null)
     {
         lock (sr_InstanceLock)
         {
             if (AppConf == null)
             {
                 try
                 {
                     AppConf = SerializerService.LoadFromFile <AppConfigService>(
                         k_FilePath,
                         typeof(AppConfigService));
                 }
                 catch (Exception)
                 {
                     AppConf = new AppConfigService {
                         StateSettings = new StateSettings()
                     };
                 }
             }
         }
     }
     return(AppConf);
 }
        public LoginResult Login()
        {
            if (LoggedInUser != null)
            {
                // user already logged in
                return(null);
            }

            AppConfigService appConfig = AppConfigService.GetInstance();

            #region Login Service

            LoginResult loginParams = FacebookService.Login("1450160541956417", // (desig patter's "Design Patterns Course App 2.4" app)
                                                            "public_profile",
                                                                                //"user_education_history",
                                                            "user_birthday",
                                                                                //"user_actions.video",
                                                                                //"user_actions.news",
                                                                                //"user_actions.music",
                                                                                //"user_actions.fitness",
                                                                                //"user_actions.books",
                                                                                //"user_about_me",
                                                            "user_friends",
                                                                                //"publish_actions",
                                                            "user_events",
                                                                                //"user_games_activity",
                                                                                //"user_groups" (This permission is only available for apps using Graph API version v2.3 or older.)
                                                            "user_hometown",
                                                            "user_likes",
                                                            //"user_location",
                                                            //"user_managed_groups",
                                                            "user_photos",
                                                            "user_posts",
                                                            //"user_relationships",
                                                            //"user_relationship_details",
                                                            //"user_religion_politics",

                                                            //"user_status" (This permission is only available for apps using Graph API version v2.3 or older.)
                                                            "user_tagged_places"
                                                            //"user_videos",
                                                            //"user_website",
                                                            //"user_work_history",
                                                            //"read_custom_friendlists",

                                                            // "read_mailbox", (This permission is only available for apps using Graph API version v2.3 or older.)
                                                            // "read_mailbox", (This permission is only available for apps using Graph API version v2.3 or older.)
                                                            //"read_page_mailboxes",
                                                            // "read_stream", (This permission is only available for apps using Graph API version v2.3 or older.)
                                                            // "manage_notifications", (This permission is only available for apps using Graph API version v2.3 or older.)
                                                            //"manage_pages",
                                                            //"publish_pages",
                                                            //"publish_actions"

                                                            //"rsvp_event"
                                                            );
            // These are NOT the complete list of permissions. Other permissions for example:
            // "user_birthday", "user_education_history", "user_hometown", "user_likes","user_location","user_relationships","user_relationship_details","user_religion_politics", "user_videos", "user_website", "user_work_history", "email","read_insights","rsvp_event","manage_pages"
            // The documentation regarding facebook login and permissions can be found here:
            // https://developers.facebook.com/docs/facebook-login/permissions#reference

            #endregion

            if (appConfig.StayLogedIn)
            {
                appConfig.LastAccessTocken = loginParams.AccessToken;
            }

            return(loginParams);
        }