Yoke

A lightweight data binding library in Swift for iOS. Yoke provides a simple API through a property wrapper called @DataBinding which can be observed from your view controllers and bound to UIKit widgets.

Currently supports two way bindings for:

Widget	Properties	Event
UIButton		.touchUpInside
UITextField	text	.editingChanged
UISwitch	isOn	.valueChanged

Usage

Binding

You can bind to any property on any UI widget (or any object that conforms to NSObject) using bind(to:on:) which takes a key path and an object and applies changes using KVC.

You can also create a two way binding with supported widgets using twoWayBind(with:).

In your view model:

@DataBinding private(set) var title = "title"
@DataBinding private(set) var isEnabled = false

init {
    $isEnabled.observe {
        // Do something when user toggles the bound switch
    }
}

From your view controller:

let titleLabel = UILabel()
let toggle = UISwitch()

func setupViews() {
    viewModel.$title
        .map { Optional($0) }
        .bind(to: \.text, on: titleLabel)

    toggle.bind(with: viewModel.$isEnabled)
}

Observation

@DataBinding can also be used as a regular observable type.

In your view model:

@DataBinding private(set) var contacts: [Contact] = []

func loadData() {
    service.fetchContacts(completion: { contacts in
        self.contacts = contacts
    })
}

From your view controller:

override func viewDidLoad() {
    super.viewDidLoad()

    viewModel.$contacts.observe { contacts in
        /* Do something with contact data */
    }
}

Using in tandem with futures

You can extend your favorite Future library to work seemlessly with Yoke.

Given a future type:

class Future<Value, Error> { /* ... */ }

Add a method that assigns the success value to a DataBinding object's wrappedValue property:

@discardablResult
func assign(to binding: DataBinding<Value>) -> Future<Value, Error> {
    onSuccess { binding.wrappedValue = $0 }

    return self
}

Once implemented, make requests from your view model:

@DataBinding var contacts: [Contact] = []

func fetchContacts() {
    service.fetchContacts()
        .receive(on: .main)
        .assign(to: $contacts)
}