public App()
        {
            //SettingsService.IsLoggedIn = true;

            // we remember if they're logged in, and only display the login page if they're not
            if (SettingsService.IsLoggedIn)
            {
                MainPage = new NavigationPage(new MasterPage(this));
            }
            else
            {
                MainPage = new LoginModalPage(this);
            }
        }
 public void Logout()
 {
     SettingsService.IsLoggedIn = false;
     MainPage = new LoginModalPage(this);
 }