试试订阅方式

 var firebase = new FirebaseClient("https://project_id.firebaseio.com/");
            firebase.Child("dataname").AsObservable<datatype>().Subscribe(obs =>
            {


                switch (obs.EventType)
                {
                    case Firebase.Database.Streaming.FirebaseEventType.InsertOrUpdate:
                        break;
                    case Firebase.Database.Streaming.FirebaseEventType.Delete:
                        break;
                    default:
                        break;
                }
            });