Settings.cs

 public static class Settings
  {
      ISettings AppSettings
      {
          get
          {
              return CrossSettings.Current;
          }
      }

      #region Setting Constants

      private const string SettingsKey = "settings_key";
      private static readonly string SettingsDefault = string.Empty;

      #endregion


      public static string GeneralSettings
      {
          get
          {
              return AppSettings.GetValueOrDefault<string>(SettingsKey, SettingsDefault);
          }
          set
          {
              AppSettings.AddOrUpdateValue<string>(SettingsKey, value);
          }
      }
}