Combine alternative to NotificationCenter

PassthroughSubject.swift

import Combine
import UIKit

class ViewModel {
    var enableSubject = PassthroughSubject<Bool, Never>() /// Similar to NotificationCenter
    var cancellables = Set<AnyCancellable>() /// Lets you store combine subscribers
}

class ViewController: UIViewController {
    let viewModel = ViewModel()

    override func viewDidLoad() {
        super.viewDidLoad()

        for index in 0 ..< 5 {
            let customView = CustomView(viewModel: viewModel)
            customView.frame = .init(x: index * 60, y: 200, width: 50, height: 50)
            customView.backgroundColor = .systemBlue
            view.addSubview(customView)
        }

        let enableButton = UIButton(type: .system)
        enableButton.setTitle("Enable", for: .normal)
        enableButton.frame = .init(x: 0, y: 300, width: 100, height: 50)
        enableButton.addTarget(self, action: #selector(enableAllViews), for: .touchUpInside)
        view.addSubview(enableButton)

        let disableButton = UIButton(type: .system)
        disableButton.setTitle("Disable", for: .normal)
        disableButton.frame = .init(x: 120, y: 300, width: 100, height: 50)
        disableButton.addTarget(self, action: #selector(disableAllViews), for: .touchUpInside)
        view.addSubview(disableButton)
    }

    @objc func enableAllViews() {
        viewModel.enableSubject.send(true) /// This will call the `.sink`s in the subviews
    }

    @objc func disableAllViews() {
        viewModel.enableSubject.send(false)
    }
}

class CustomView: UIView {
    let viewModel: ViewModel
    init(viewModel: ViewModel) {
        self.viewModel = viewModel
        super.init(frame: .zero)

        viewModel.enableSubject.sink { enable in
            self.isUserInteractionEnabled = enable
            self.backgroundColor = enable ? .systemGreen : .systemRed
        }
        .store(in: &viewModel.cancellables) /// Must store this subscriber/cancellable so that it's kept alive!
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

Published.swift

/// Here's an alternative via a `@Published` property.
/// There's one thing to keep in mind — `.sink`s on `@Published` properties get called immediately,
/// so if you don't want this, add a `dropFirst`.
/// See https://stackoverflow.com/q/60568858/14351818 for more info.

import Combine
import UIKit

class ViewModel {
    @Published var isEnabled = false
    var cancellables = Set<AnyCancellable>() /// Lets you store combine subscribers
}

class ViewController: UIViewController {
    let viewModel = ViewModel()

    override func viewDidLoad() {
        super.viewDidLoad()

        for index in 0 ..< 5 {
            let customView = CustomView(viewModel: viewModel)
            customView.frame = .init(x: index * 60, y: 200, width: 50, height: 50)
            /// `CustomView`'s `viewModel.$isEnabled.sink` sets the background color **initially**, so no need to set anything here.
            view.addSubview(customView)
        }

        let enableButton = UIButton(type: .system)
        enableButton.setTitle("Enable", for: .normal)
        enableButton.frame = .init(x: 0, y: 300, width: 100, height: 50)
        enableButton.addTarget(self, action: #selector(enableAllViews), for: .touchUpInside)
        view.addSubview(enableButton)

        let disableButton = UIButton(type: .system)
        disableButton.setTitle("Disable", for: .normal)
        disableButton.frame = .init(x: 120, y: 300, width: 100, height: 50)
        disableButton.addTarget(self, action: #selector(disableAllViews), for: .touchUpInside)
        view.addSubview(disableButton)
    }

    @objc func enableAllViews() {
        viewModel.isEnabled = true
    }

    @objc func disableAllViews() {
        viewModel.isEnabled = false
    }
}

class CustomView: UIView {
    let viewModel: ViewModel
    init(viewModel: ViewModel) {
        self.viewModel = viewModel
        super.init(frame: .zero)

        viewModel.$isEnabled
            /// Note, if you observe a single `@Published` property, the `.sink` is fired initially too.
            /// You can avoid this by inserting `.dropFirst()` just before `.sink`.
            .sink { enable in
                self.isUserInteractionEnabled = enable
                self.backgroundColor = enable ? .systemGreen : .systemRed
            }
            .store(in: &viewModel.cancellables)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

Result:

RPReplay_Final1659200899.mp4