Swift Networking using Combine - ios

Question

I am trying to make network requests to download data and put it into a UITableView. I am not sure what I am doing wrong but when I call viewModel.request() in the ViewController it is not populating the UITableView.
I left some of the code out to make it simple but the UITableView works fine when using URLSession, I just can't get it to work with Combine.
If I print viewModel.sections in viewDidLoad(), it prints an empty array:
ViewController
class ViewController: UIViewController {
var viewModel = TestViewModel()
override func viewDidLoad() {
super.viewDidLoad()
//TableView Setup
setUpTableView()
viewModel.request()
self.tableView.reloadData()
}
func numberOfSections(in tableView: UITableView) -> Int {
return viewModel.sections.count
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return viewModel.sections[section].sports.count
}
}
TestViewModel
class TestViewModel {
#Published var sections: [Sections] = []
var date: Date = Date()
var cancellables: AnyCancellable?
func request(){
let nfl = NetworkManager.download(endpoint: .nfl, date: date.query())
.decode(type: EventModel.self, decoder: JSONDecoder())
let nba = NetworkManager.download(endpoint: .nba, date: date.query())
.decode(type: EventModel.self, decoder: JSONDecoder())
let mlb = NetworkManager.download(endpoint: .mlb, date: date.query())
.decode(type: EventModel.self, decoder: JSONDecoder())
let nhl = NetworkManager.download(endpoint: .nhl, date: date.query())
.decode(type: EventModel.self, decoder: JSONDecoder())
self.cancellables = Publishers.Zip4(nfl, nba, mlb, nhl)
.eraseToAnyPublisher()
.sink(receiveCompletion: { (completion) in
switch completion {
case .finished:
break
case .failure(let error):
print("Error:",error.localizedDescription)
}
}, receiveValue: { [weak self] (nfl, nba, mlb, nhl) in
var section: [Sections] = []
if !nfl.events.isEmpty {
section.append(.init(icon: "football.fill", title: "NFL", sports: nfl.events, leagues: nfl.leagues))
}
if !nba.events.isEmpty {
section.append(.init(icon: "basketball.fill", title: "NBA", sports: nba.events, leagues: nba.leagues))
}
if !mlb.events.isEmpty {
section.append(.init(icon: "baseball.fill", title: "MLB", sports: mlb.events, leagues: mlb.leagues))
}
if !nhl.events.isEmpty {
section.append(.init(icon: "hockey.puck.fill", title: "NHL", sports: nhl.events, leagues: nhl.leagues))
}
self?.sections = section
})
// This is Empty
print(self.sections)
}
}
NetworkManager
class NetworkManager {
static func download(endpoint: Endpoint, date: String) -> AnyPublisher<Data, Error> {
let url = URL(string: "***API URL***")!
let final = url.appendingPathComponent(endpoint.build())
var components = URLComponents(url: final, resolvingAgainstBaseURL: true)!
components.queryItems = [
URLQueryItem(name: "dates", value: date),
]
let request = URLRequest(url: components.url!)
return
URLSession.shared.dataTaskPublisher(for: request)
.subscribe(on: DispatchQueue.global(qos: .background))
.tryMap{(data, response) -> Data in
guard let response = response as? HTTPURLResponse,
response.statusCode >= 200 && response.statusCode < 300 else {
throw URLError(.badServerResponse)
}
return data
}
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher()
}
}

Answer 1

You’re using SwiftUI #Published method in UIKit. What works best is CurrentValueSubject for UIKit.
Change you sections to be var sections CurrentValueSubject<[Sections], Never>([]) in your VM. Then in your VM request function, build up the sections data (_values) and send by sections.send(_values)
In your controller you need to bind to the VM.sections by viewModel.sections.sink { in $0 } where $0 is your data.