error while returning data from firebase in xamarin app-CodePudding

I have a c# appliction which is deal with firebase data base on order to get data from it for specific item, An object reference is required for the non-static field, method, or property return this error in AppintmentService.GetFollowUp(patient.ID) line, what is the mistake i did ?

public ICommand Appearing { get => _Appearing; set => SetProperty(ref _Appearing, value, nameof(Appearing)); }

 public PatientProfileFollowUpPageModelView(Patient patient)
        {
            Appearing = new AsyncCommand(async () => await LoadData(patient));
        }

The function :

async Task LoadData(Patient patient)
        {
            Appoitments = new ObservableCollection<Appoitment>(await AppintmentService.GetFollowUp(patient.ID));

        }

and the service :

public ObservableCollection<Appoitment> GetFollowUp(string PatientID)
        {
            var FollowUp = firebaseClient
             .Child($"Specalists/{PreferencesConfig.Id}/Patients/{PatientID}/Appointments")
             .AsObservable<Appoitment>()
             .AsObservableCollection();

            return FollowUp;
        }

CodePudding user response：

GetFollowUp is a method on the class AppintmentService, so you need an instance of AppintmentService in order to call it.

var svc = new AppintmentService);
var result = svc.GetFollowUp(patient.ID)

alternately, you can make GetFollowUp a static method, which would allow you to call it without having an instance

in either case, GetFollowUp is not marked async, so calling it using await is not neccessary