Medium article: SLC part 1 - ViewController base

SceneController.swift

import RxSwift

class SceneController<View>: UIViewController where View: UIView & ViewModelled {
    typealias ViewModel = View.ViewModel

    private let bag = DisposeBag()
    private let viewModel: ViewModel

    // We omit some additional "AbstractTarget" wrappers taking these `PublishSubjects` as arguments
    // used to create `Selector` for `UIBarButtonItem` creation.
    private let rightBarButtonSubject = PublishSubject<Void>()
    private let leftBarButtonSubject = PublishSubject<Void>()

    // MARK: - Initialization
    required init(viewModel: ViewModel) {
        self.viewModel = viewModel
        super.init(nibName: nil, bundle: nil)
        setup()
    }

    required init?(coder: NSCoder) { fatalError("InterfaceBuilder support omitted.") }

    // MARK: View Lifecycle
    override func loadView() {
        view = View()
        view.backgroundColor = .white
        // We should not use autolayout here, but this works.
        view.bounds = UIScreen.main.bounds
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Here we can actually also setup titles and navigation bar using some protocol magic.
    }
}

// MARK: Private
private extension SceneController {

    func setup() {
        bindViewToViewModel()
        edgesForExtendedLayout = .bottom
    }

    func bindViewToViewModel() {
        guard let contentView = view as? View else { fatalError("Incorrect implementation, set `view` to an instance of `View` inside `loadView()`.") }

        // We omit some PublishSubjects for `title` and `navigationBar` items content.
        let controllerInput = ControllerInput(
            viewDidLoad: rx.viewDidLoad,
            viewWillAppear: rx.viewWillAppear,
            viewDidAppear: rx.viewDidAppear,
            leftBarButtonTrigger: leftBarButtonSubject.asDriverOnErrorReturnEmpty(),
            rightBarButtonTrigger: rightBarButtonSubject.asDriverOnErrorReturnEmpty()
        )

        // The `View` passed as a generic conforms to `ViewModelled`
        // a protocol declaring the `inputFromView` getter.
        let inputFromView = contentView.inputFromView

        let input = ViewModel.Input(fromView: inputFromView, fromController: controllerInput)

        // Transform input from view and controller into output used to update UI
        // Navigatoin logic is handled by the Coordinator listening to navigation
        // steps in passed to the ViewModels `navigator` (`Stepper`).
        let output = viewModel.transform(input: input)

        // Update UI, dispose the array of `Disposable`s
        contentView.populate(with: output).forEach { $0.disposed(by: bag) }
    }
}