Update data using MVVM architecture in swift - swift

Question

I am using MVVM Architecture for learning to develop a small weather application for learning purposes.
View
class ViewController: UIViewController {
private var cityDataViewModel = CityDataViewModel()
private var data = [ConsolidatedWeather]()
#IBOutlet weak var label1: UILabel!
#IBOutlet weak var label2: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
loadCityData()
}
func loadCityData(){
print("loadCityData")
cityDataViewModel.getCityData {
}
}
}
ViewModel
class CityDataViewModel{
private var networkManager = CityNetworkManager()
private var weatherNetworkManager = WeatherNetworkManager()
var weatherModel = [ConsolidatedWeather]()
var myStruct :[WeatherModel] = []
var weatherState: String?
var minTemp: Double?
var maxTemp: Double?
var currentTemperature: Double?
var summary: String?
var dateString: String = ""
//MARK: - Get cityInformation
func getCityData(completion: #escaping () -> ()) {
networkManager.getCityDataNetworkCall { [weak self](result) in
switch result{
case .success(let information):
information.forEach { (data) in
print("\(data.title) || \(data.locationType) || \(data.woeid) || \(data.lattLong)")
print("loadCityData 3")
self?.getCityWeatherInformation(with: data.woeid)
print("loadCityData 4")
}
completion()
case .failure(let error):
print(error)
}
}
}
//MARK: - Get Weather data
func getCityWeatherInformation(with woeid: Int){
//[weak self]
weatherNetworkManager.getWeatherDataNetworkCall(cityId: woeid) {[weak self] (result) in
print("loadCityData 5")
switch result{
case .success(let listOfData):
self?.weatherModel = listOfData.consolidatedWeather
}
case .failure(let error):
print(error)
}
}
}
var ttile: String{
return weatherState ?? ""
}
}
From the view, I am sending a call to ViewModel to get cityId by using func getCityDat()
After get the cityId I called func getCityWeatherInformation(with woeid: Int) for get details weather data. I am successfully getting those data from server.
How can I send that information to view for updating my viewController?

Answer 1

Setting up a protocol/closure system as mentioned in the comments is certainly a popular option.
As of iOS 13, you also have the option of using Combine to publish the changes on your ViewModel, which can trigger the ViewController to update.
A simplified example:
import Combine
import UIKit
class MyVC : UIViewController {
private var label = UILabel()
private var label2 = UILabel()
private var viewModel = ViewModel()
private var cancellables = Set<AnyCancellable>()
override func viewDidLoad() {
addLabels()
linkPublishers()
viewModel.getData()
}
func linkPublishers() {
//OPTION 1
viewModel.objectWillChange.sink { (_) in
DispatchQueue.main.async {
self.label.text = self.viewModel.text1
self.label2.text = self.viewModel.text2
}
}
.store(in: &cancellables)
// **** OR ****
//OPTION 2
viewModel
.$text1
.receive(on: RunLoop.main)
.sink { (newLabelText) in
self.label.text = newLabelText
}.store(in: &cancellables)
viewModel
.$text2
.receive(on: RunLoop.main)
.sink { (newLabelText) in
self.label2.text = newLabelText
}.store(in: &cancellables)
}
func addLabels() {
label.frame = CGRect(x: 0, y: 0, width: 200, height: 40)
self.view.addSubview(label)
label2.frame = CGRect(x: 0, y: 40, width: 200, height: 40)
self.view.addSubview(label2)
}
}
class ViewModel : ObservableObject {
#Published var text1 = ""
#Published var text2 = ""
func getData() {
DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
self.text1 = "Hello, world"
}
DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
self.text2 = "Hello, world 2"
}
}
}
The ViewModel here does a fake task mocking an async network call. Then, it sets one of its #Published properties to the result of that data.
Back in the ViewController, linkPublishers has two different ways of hooking up those published properties:
Observing objectWillChange, which gets triggered before any of the published properties update
Observing each #Published property independently.