Better alternative to DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) for data refresh - swift

Question

I am looking for a better alternative to DispatchQueue.main.asyncAfter(deadline: .now() + 0.5 to refresh my data.
My data is dynamic and changes based on user action, it's important that the data the user sees is always up to date.
I am using Firebase Realtime Database, I am wondering whether I can alter my service file to refetch data any time something changes. here is my service file:
class Service {
static let shared = Service()
let BASE_URL = "https://firebaseurl.com/jsondata.json"
let calendar = Calendar.current
func fetchClient(completion: #escaping ([Calls]) -> ()) {
guard let url = URL(string: BASE_URL) else { return }
URLSession.shared.dataTask(with: url) { (data, response, error) in
// handle error
if let error = error {
print("Failed to fetch data with error: ", error)
return
}
guard let data = data else {return}
do {
let myDecoder = JSONDecoder()
myDecoder.dateDecodingStrategy = .secondsSince1970
let calls = try myDecoder.decode([Calls?].self, from: data).filter({
self.calendar.isDateInToday($0?.dateTime ?? Date(timeIntervalSinceReferenceDate: -123456789.0))
})
completion(calls.filter{$0?.callmade != true}.compactMap{ $0 })
} catch let error {
print("Failed to create JSON with error: ", error)
}
}.resume()
}
}
Currently in my Main Controller I am using:
func fetchClient() {
Service.shared.fetchClient { (client) in
DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
self.client = client
self.collectionView.reloadData()
self.fetchClient()
}
}
}

Answer 1

You can use Realtime Database to observer changes in data.
https://firebase.google.com/docs/database/ios/read-and-write#listen_for_value_events