state-with-enums.swift

import UIKit

protocol ViewModelType {
}

protocol Service {
    func request(_ path: String, completion: @escaping ([String]) -> Void)
}

struct MainViewModel: ViewModelType {
    private(set) var service: Service
    
    init(_ service: Service) {
        self.service = service
    }
    
    func getMainArticles(completion: @escaping ([String]) -> Void) {
        service.request("/path/articles", completion: completion)
    }
    
    func articlesLoaded(_ articles: [String]) {
        
    }
}

class MainViewController: UIViewController {
    
    enum State {
        case loading
        case loaded([String])
        case error
        case no
    }
    
    private(set) var viewModel: MainViewModel
    private let indicator = UIActivityIndicatorView(frame: .zero)
    private let tableView = UITableView(frame: .zero)
    
    private var state: State = .no {
        didSet {
            switch state {
            case .loading:
                indicator.startAnimating()
            case .loaded(let articles):
                viewModel.articlesLoaded(articles)
                tableView.reloadData()
                indicator.stopAnimating()
            case .error:
                print("Show error state!")
            case .no:
                print("This is the default state")
            }
        }
    }
    
    init(_ viewModel: MainViewModel) {
        self.viewModel = viewModel
        super.init(nibName: nil, bundle: nil)
    }
    
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.addSubview(indicator)
        view.addSubview(tableView)
    }
    
    // triggered somewhere
    private func callArticles() {
        
        state = .loading
        
        viewModel.getMainArticles { [weak self] articles in
            self?.state = .loaded(articles)
        }
    }
}