SwiftUI: Data in list appears sometimes and sometimes not - json

Question

I have a problem. In my application, I have CoreData with devices and the IP of the devices. I want to make an API request to fetch JSON data from a selected device and show them in a list. My problem is that sometimes it works and sometimes it does not and the list does not update when I change the data. I hope someone can help me.
BouquetAPIModel.swift
struct BouquetAPIModel: Codable {
let success: String
let data: DataClass
}
// MARK: - DataClass
struct DataClass: Codable {
let bouquets: [Bouquet]
}
// MARK: - Bouquet
struct Bouquet: Codable {
var number, name: String
}
Device.swift
public class Device: NSManagedObject, Identifiable {
#Published var bouquets : [Bouquet] = [Bouquet]()
func fetchBouquetList() {
fetchAPIRequest(apiPath: "/control/getbouquets?format=json") { (res: Result<BouquetAPIModel, Error>) in
switch res {
case .success(let bouquets):
self.bouquets = bouquets.data.bouquets
case .failure(let err):
print("Fail to fetch bouquets: ", err)
}
}
}
fileprivate func fetchAPIRequest<T: Decodable>(apiPath: String, completion: #escaping (Result<T, Error>) -> ()) {
let urlString = getApiUrl(apiPath: apiPath)
guard let url = URL(string: urlString) else { return }
URLSession.shared.dataTask(with: url) { (data,resp, err) in
if let err = err {
completion(.failure(err))
return
}
do {
let welcome = try JSONDecoder().decode(T.self, from: data!)
completion(.success(welcome))
} catch let jsonError {
completion(.failure(jsonError))
}
}.resume()
}
BouquetView.swift
import SwiftUI
struct BouquetView: View {
#Binding var device : Device?
#State var bouquets: [Bouquet] = [Bouquet]()
var body: some View {
VStack {
Text(String(device?.deviceName ?? "fehler")).onTapGesture {
self.device?.bouquets.removeFirst()
print("Touch")
}
List (self.bouquets, id: \Bouquet.name) { bouquet in
VStack(alignment: .leading) {
Text(bouquet.name)
}
}
}.onAppear(perform: loadBouquets)
}
func loadBouquets() {
if device == nil {
//TODO jumo to settings
}
else {
device?.fetchBouquetList()
self.bouquets = device!.bouquets
}
}
}
struct BouquetView_Previews: PreviewProvider {
static var previews: some View {
BouquetView(device: .constant(nil))
}
}

Answer 1

Can you update your Device like below?
public class Device: ObservableObject, Identifiable {
...
}
And make sure you declare your device with annotation #ObservedObject before passing to BouquetView

Answer 2

Fetching might be long, so you've got into racing. To avoid it the followings approach might be used
1) remove the following line as data might not be ready yet at this point
self.bouquets = device!.bouquets
2) add explicit listener for data set
if device == nil {
//TODO jumo to settings
device!.$bouquets
.assign(to: \.bouquets, on: self)
.store(in: &cancellables) // << you will need to create this store var
}