Delegate_vs_<Void,NoError>.swift

// MARK: Delegate approach

import UIKit

protocol ExampleViewModelDelegate: class {
    func someEventDidOccur()
}

class ExampleViewModel {
    weak var delegate: ExampleViewModelDelegate?
    
    func someHandler() {
        delegate?.someEventDidOccur()
    }
}

class ExampleViewController : UIViewController {
    var viewModel = ExampleViewModel()
    
    public override func viewDidLoad() {
        super.viewDidLoad()
        
        viewModel.delegate = self
    }
}

extension ExampleViewController: ExampleViewModelDelegate {
    func someEventDidOccur() {
        // handle the event
    }
}

// MARK: Reactive approach

import UIKit
import ReactiveCocoa

class ExampleViewModel {
    var someEvent: SignalProducer<Void, NoError> = SignalProducer { sink, _ in
        sink.send(value: ())
        sink.sendCompleted()
    }
}

class ExampleViewController : UIViewController {
    var viewModel = ExampleViewModel()
    
    public override func viewDidLoad() {
        super.viewDidLoad()
        
        viewModel.someEvent.startWithValues {
            // handle the event
        }
    }
}