Swift api observable not working without wait - ios

Question

Hi I'm fetching data from a local api in a LocationsDataService class and assigning this as a #Published var in the data service and then using this in my LocationsViewModel. If I wait for my api request to complete, for example;
DispatchQueue.main.asyncAfter(deadline: .now() + 3.0) {
let locations = dataService.locations
self.locations = locations
}
Then the locations are rendered on the screen.
This is my data service class;
//
// LocationsDataService.swift
// MapTest
//
//
import Foundation
import MapKit
import Combine
class LocationsDataService: ObservableObject {
let token = "2|asOnUG27uCrcVuGxOO65kS25mX0nUSls5ApfemQy";
#Published var locations: [Location] = []
public var cancellable: AnyCancellable?
enum HTTPError: LocalizedError {
case statusCode
}
init() {
fetch()
}
func fetch() {
guard let url = URL(string: "http://localhost:8080/api/locations") else {
print("Invalid url...")
return
}
var urlRequest = URLRequest(
url: url
)
urlRequest.setValue(
"Bearer \(token)",
forHTTPHeaderField: "Authorization"
)
self.cancellable = URLSession.shared.dataTaskPublisher(for: urlRequest)
.tryMap { output in
guard let response = output.response as? HTTPURLResponse, response.statusCode == 200 else {
throw HTTPError.statusCode
}
return output.data
}
.decode(type: [Location].self, decoder: JSONDecoder())
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher()
.sink(receiveCompletion: { completion in
switch completion {
case .finished:
break
case .failure(let error):
fatalError(error.localizedDescription)
}
}, receiveValue: { locations in
self.locations = locations
})
}
}
And this is my view model
//
// LocationsViewModel.swift
// CoffeeShops
//
//
import Foundation
import MapKit
import SwiftUI
class LocationsViewModel: ObservableObject {
// all loaded locations
#Published var locations: [Location]
init() {
let dataService = LocationsDataService() // the init function will do the api call
self.locations = [Location(
name: "Amsterdam",
address: "Amsterdam",
latitude: 52.3721009,
longitude: 4.8912196,
description: "Amsterdam",
imageNames: [],
link: "https://en.wikipedia.org/wiki/Colosseum")]
DispatchQueue.main.asyncAfter(deadline: .now() + 3.0) {
let locations = dataService.locations
self.locations = locations
print(locations)
}
}
}
I'm not sure why I need to explicitly wait for the api before assigning it to the locations in the LocationsViewModel as the LocationsDataService.locations is #Published var locations: [Location] = [], therefore I thought it would be observed. Obviously it wouldn't be great to have to put in a time limit before I can update the screen as it could be done in 1 second or 5 seconds. Any ideas what I'm doing wrong?

Answer 1

ObservableObject will make SwiftUI view to update the view when #Published changes. But when you're creating one ObservableObject inside an other one, there's no way it can automatically work.
You don't actually need ObservableObject for your service, you only need #Published for you property, and and there's how you can sync it with your view model:
private var cancellable: AnyCancellable?
init() {
cancellable = dataService.$locations.sink(receiveValue: { locations in
self.locations = locations
})
}