GeofenceListeners.cs

public class CreateGeoFailListener : Java.Lang.Object, IOnFailureListener
{
      private Activity mainActivity;

      public CreateGeoFailListener(Activity mainActivity)
      {
          this.mainActivity = mainActivity;
      }

      public void OnFailure(Java.Lang.Exception ex)
      {
       Toast.MakeText(mainActivity, "Geofence request failed: " + GeofenceErrorCodes.GetErrorMessage((ex as ApiException).StatusCode), ToastLength.Long).Show();
      }
}

public class CreateGeoSuccessListener : Java.Lang.Object, IOnSuccessListener
{
     private Activity mainActivity;
     public CreateGeoSuccessListener(Activity mainActivity)
     {
         this.mainActivity = mainActivity;
     }
     public void OnSuccess(Java.Lang.Object data)
     {
        Toast.MakeText(mainActivity, "Geofence request successful", ToastLength.Long).Show();
     }
}