Usage of MVVM in iOS

Question

I\'m an iOS developer and I\'m guilty of having Massive View Controllers in my projects so I\'ve been searching for a better way to structure my projects and came across the MVV

Answer 1

MVVM architecture in iOS can be easily implemented without using third party dependencies. For data binding, we can use a simple combination of Closure and didSet to avoid third-party dependencies.

public final class Observable {

    private var closure: ((Value) -> ())?

    public var value: Value {
        didSet { closure?(value) }
    }

    public init(_ value: Value) {
        self.value = value
    }

    public func observe(_ closure: @escaping (Value) -> Void) {
        self.closure = closure
        closure(value)
    }
}

An example of data binding from ViewController:

final class ExampleViewController: UIViewController {

    private func bind(to viewModel: ViewModel) {
        viewModel.items.observe(on: self) { [weak self] items in
            self?.tableViewController?.items = items
            // self?.tableViewController?.items = viewModel.items.value // This would be Momory leak. You can access viewModel only with self?.viewModel
        }
        // Or in one line:
        viewModel.items.observe(on: self) { [weak self] in self?.tableViewController?.items = $0 }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        bind(to: viewModel)
        viewModel.viewDidLoad()
    }
}

protocol ViewModelInput {
    func viewDidLoad()
}

protocol ViewModelOutput {
    var items: Observable<[ItemViewModel]> { get }
}

protocol ViewModel: ViewModelInput, ViewModelOutput {}
final class DefaultViewModel: ViewModel {  
  let items: Observable<[ItemViewModel]> = Observable([])

  // Implmentation details...
}

Later it can be replaced with SwiftUI and Combine (when a minimum iOS version in of your app is 13)

In this article, there is a more detailed description of MVVM https://tech.olx.com/clean-architecture-and-mvvm-on-ios-c9d167d9f5b3