swiftUI / Xcode 12 fetch data from server - json

Question

I'm very new to swiftUI and have been working through the landscapes app tutorial.
I have been trying to switch the data source from a bundled JSON file to a remote JSON source but have so far been lost on how to integrate what I've learnt about the URLSession with the tutorials load code.
Apple's code:
final class ModelData: ObservableObject {
#Published var landmarks: [Landmark] = load("landmarkData.json")
// #Published var landmarks: [Landmark] = apiCall.getLocations(locations)
}
func load<T: Decodable>(_ filename: String) -> T {
let data: Data
guard let file = Bundle.main.url(forResource: filename, withExtension: nil)
else {
fatalError("Couldn't find \(filename) in main bundle.")
}
do {
data = try Data(contentsOf: file)
} catch {
fatalError("Couldn't load \(filename) from main bundle:\n\(error)")
}
do {
let decoder = JSONDecoder()
return try decoder.decode(T.self, from: data)
} catch {
fatalError("Couldn't parse \(filename) as \(T.self):\n\(error)")
}
}
What I have to load from the remote source:
struct Location: Codable, Identifiable {
let id = UUID()
let country: String
let name: String
}
class apiCall {
func getLocations(completion:#escaping ([Location]) -> ()) {
guard let url = URL(string: "https://overseer.cyou/heritage/heritageData.json") else { return }
URLSession.shared.dataTask(with: url) { (data, _, _) in
let locations = try! JSONDecoder().decode([Location].self, from: data!)
print(locations)
DispatchQueue.main.async {
completion(locations)
}
}
.resume()
}
}
Can anyone show me how I go about doing this, ideally from a complete beginners point of view?

Answer 1

// framework support
import SwiftUI
import Combine
// List view setup
struct LocationsView: View {
#ObservedObject var viewModel = LocationModel()
var body: some View {
List(viewModel.locations) { location in
HStack {
VStack(alignment: .leading) {
Text(location.name)
.font(.headline)
Text(location.country)
.font(.subheadline)
}
}
}
}
}
// Location model
struct Location: Codable, Identifiable {
var id = UUID()
let country: String
let name: String
let locationId: Int = 0
enum CodingKeys: String, CodingKey {
case locationId = "id"
case country
case name
}
}
// Location view model class
class LocationModel: ObservableObject {
#Published var locations: [Location] = []
var cancellationToken: AnyCancellable?
init() {
getLocations()
}
}
extension LocationModel {
func getLocations() {
cancellationToken = self.request("https://overseer.cyou/heritage/heritageData.json")?
.mapError({ (error) -> Error in
print(error)
return error
})
.sink(receiveCompletion: { _ in },
receiveValue: {
self.locations = $0
})
}
// API request
private func request(_ path: String) -> AnyPublisher<[Location], Error>? {
guard let url = URL(string: path)
else { return nil }
let request = URLRequest(url: url)
return apiCall.run(request)
.map(\.value)
.eraseToAnyPublisher()
}
}
// API setup
struct apiCall {
struct Response<T> {
let value: T
let response: URLResponse
}
static func run<T: Decodable>(_ request: URLRequest) -> AnyPublisher<Response<T>, Error> {
return URLSession.shared
.dataTaskPublisher(for: request)
.tryMap { result -> Response<T> in
let value = try JSONDecoder().decode(T.self, from: result.data)
return Response(value: value, response: result.response)
}
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher()
}
}