Code composition of SwiftUI when the model is passed from parent and dependend on parents setup - swift

Question

How to structure the #ObservedObject, #State, #StateObject for a situation like this
i have a box which displays next and previous appointment (NextPreviousAppointmentBoxUI)
this NextPreviousAppointmentBoxUI uses a generic appointment box (SingleAppointmentBoxUI), which loads and appointment by the configuration of the model (FAppointmentsStore) provided by the parent
this model is however dependent on the appointment given to NextPreviousAppointmentBoxUI from above
i restructred the code several times, but still not sure how the SwiftUI composition should look like in such case
how to avoid setupAndLoadModels be called .onChange and .onAppear and be called just once? Is there a more suitabl composition?
class FAppointmentsStore: ObservableObject {
#Published state: State = .loading
...
}
class FAppointment: RealmObject {
...
}
struct SingleAppointmentBoxUI: View {
#ObservedObject var model: FAppointmentsStore
var body: some View {
Group {
switch model.loadingState {
case .loading:
Text("Loading")
case .loaded:
if let appointment = model.appointment {
Text("Display appointment \(appointment.title)")
}
case .error:
Text("Error")
}
}
}
}
struct NextPreviousAppointmentBoxUI: View {
var appointment: FAppointment
#State var nextModel: FAppointmentsStore?
#State var previousModel: FAppointmentsStore?
var body: some View {
VStack {
if let nextModel = nextModel, let previousModel = previousModel {
Text("Previous")
SingleAppointmentBoxUI(model: previousModel)
Divider()
Text("Next")
SingleAppointmentBoxUI(model: nextModel)
}
}
.onAppear {
setupAndLoadModels(appointment)
}
.onChange(of: appointment, perform: { newValue in
setupAndLoadModels(newValue)
})
}
func setupAndLoadModels(_ appointment: FAppointment?) {
guard let user = appointment.user, let start = appointment.start, let end = appointment.end else {
return
}
nextModel = FAppointmentsStore(user: user, startFrom: end, limit: 1, sort: .startAsc)
previousModel = FAppointmentsStore(user: user, startTo: start, limit: 1, sort: .startDesc)
nextModel?.loadContent()
previousModel?.loadContent()
}
}