Bindings for Combine
Unidirectional binding operators and reactive extensions for Cocoa classes.
The operators
Bindings provides two operators: <~
, the input binding operator, and
~>
, the output binding operator.
Input bindings update the state of your UI
import Bindings
import UIKitBindings
nameLabel.reactive.text <~ viewModel.fullName
Output bindings respond to changes
nameField.reactive.edited ~> viewModel.setName
UIApplication.reactive.didBecomeActiveNotification ~> viewModel.refresh
Common bindings for system classes
In addition to the core operator definitions, Bindings also provides conveniences for using bindings with many system classes. Take a look at the following modules to see what's provided (and consider contributing!):
UIKitBindings
for apps using UIKit (iOS, iPadOS, Catalyst and more)- More to come...
Reactive extensions
It's convenient to group reactive extensions into their own namespace, especially when extending types you don't own with reactive APIs.
Use the ReactiveExtensionProvider
protocol to define the .reactive
property
on your types:
extension MyViewModel: ReactiveExtensionProvider {}
Then add reactive extensions via the Reactive
type:
extension UserDefaults {
var username: String? {
get { string(forKey: "username") }
set { set(newValue, forKey: "username") }
}
}
extension Reactive where Base: UserDefaults {
var username: NSObject.KeyValueObservingPublisher<Base, String?> {
base.publisher(for: \.username)
}
}
UserDefaults.standard.reactive.username.sink { username in
print("New username: \(username)")
}
Bindings last for the lifetime of their owner
In Combine, the AnyCancellable
class controls the lifetime of a subscription.
Subscriptions can be automatically cancelled by using the store(in:)
method:
import UIKit
class MyViewController: UIViewController {
@IBOutlet private var usernameLabel: UILabel!
private var subscriptions: [AnyCancellable] = []
override func viewDidLoad() {
super.viewDidLoad()
UserDefaults.standard.reactive.username
.sink { [usernameLabel] in usernameLabel?.text = $0 }
.store(in: &subscriptions)
}
}
Bindings encapsulates this pattern with the BindingOwner
protocol, which
automatically defines a subscriptions
collection on all conforming classes.
The BindingSink
subscriber then automatically disposes of the binding
subscription when its owner
goes out of scope:
extension Reactive where Base: UILabel {
var text: BindingSink<Base, String?> {
BindingSink(owner: base) { label, newValue in
label.text = newValue
}
}
}
// automatically cancelled when `usernameLabel` goes out of scope
usernameLabel.reactive.text <~ UserDefaults.standard.reactive.username
Contributing
Have a useful reactive extension in your project? Please consider contributing it back to the community!
For more details, see the CONTRIBUTING document. Thank you, contributors!
License
Bindings is Copyright (c) 2019 thoughtbot, inc. It is free software, and may be redistributed under the terms specified in the LICENSE file.
About
Bindings is maintained and funded by thoughtbot, inc. The names and logos for thoughtbot are trademarks of thoughtbot, inc.
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