ReactKit

Swift Reactive Programming.

How to install

See Wiki page.

Example

For UI Demo, please see ReactKit/ReactKitCatalog.

Key-Value Observing

// create signal via KVO
self.obj1Signal = KVO.signal(obj1, "value")

// bind signal via KVC (<~ as binding operator)
(obj2, "value") <~ self.obj1Signal

XCTAssertEqual(obj1.value, "initial")
XCTAssertEqual(obj2.value, "initial")

obj1.value = "REACT"

XCTAssertEqual(obj1.value, "REACT")
XCTAssertEqual(obj2.value, "REACT")

To remove signal-bindings, just release signal itself.

self.obj1Signal = nil   // release signal & its bindings

obj1.value = "Done"

XCTAssertEqual(obj1.value, "Done")
XCTAssertEqual(obj2.value, "REACT")

NSNotification

self.signal = Notification.signal("MyNotification", obj1).map { notification -> NSString? in
    return "hello" // convert NSNotification? to NSString?
}

(obj2, "value") <~ self.signal

Normally, NSNotification itself is useless value for binding with other objects, so use signal-operations e.g. map(f: T -> U) to convert it.

Target-Action

// UIButton
self.buttonSignal = self.button.buttonSignal("OK")

// UITextField
self.textFieldSignal = self.textField.textChangedSignal()

^{ println($0) } <~ self.buttonSignal     // prints "OK" on tap

// NOTE: ^{ ... } = closure-first operator, same as `signal ~> { ... }`
^{ println($0) } <~ self.textFieldSignal  // prints textField.text on change

Complex example

The example below is taken from

• iOS - ReactiveCocoaをかじってみた - Qiita (well-illustrated)

where it describes 4 UITextFields which enables/disables UIButton at certain condition:

let usernameTextSignal = self.usernameTextField.textChangedSignal()
let emailTextSignal = self.emailTextField.textChangedSignal()
let passwordTextSignal = self.passwordTextField.textChangedSignal()
let password2TextSignal = self.password2TextField.textChangedSignal()

let anyTextSignal = Signal.any([usernameTextSignal, emailTextSignal, passwordTextSignal, password2TextSignal])

// create button-enabling signal via any textField change
self.buttonEnablingSignal = anyTextSignal.map { (values, changedValue) -> NSNumber? in

    let username: NSString? = values[0]?
    let email: NSString? = values[1]?
    let password: NSString? = values[2]?
    let password2: NSString? = values[3]?

    // validation
    let buttonEnabled = username?.length > 0 && email?.length > 0 && password?.length >= MIN_PASSWORD_LENGTH && password? == password2?

    // NOTE: use NSNumber because KVO does not understand Bool
    return NSNumber(bool: buttonEnabled)
}

// REACT: enable/disable okButton
(self.okButton, "enabled") <~ self.buttonEnablingSignal!

For more examples, please see XCTestCases.

How it works

ReactKit is based on powerful SwiftTask (JavaScript Promise-like) library, allowing to deliver multiple events (KVO, NSNotification, Target-Action, etc) continuously over time using its progress feature (<~ operator in ReactKit).

Unlike many Reactive Extensions (Rx) libraries including ReactiveCocoa which has a basic concept of "hot" and "cold" signals, ReactKit gracefully integrated them into one hot + paused (lazy) signal Signal<T> class as well as not adopting the concept of Disposable but using signal.cancel() feature instead.

Also in ReactKit, Rx's signal.subscribe(onNext, onError, onComplete) method is interpreted as signal.progress() (<~) and signal.then()/success()/failure() separately. When they are called on needs, they will start lazy evaluation.

Methods

Signal Operations

• Instance Methods
  • filter(f: T -> Bool)
  • filter2(f: (old: T?, new: T) -> Bool)
  • map(f: T -> U)
  • flatMap(f: T -> Signal<U>)
  • map2(f: (old: T?, new: T) -> U)
  • mapAccumulate(initialValue, accumulator) (alias: scan)
  • take(count)
  • takeUntil(signal)
  • skip(count)
  • skipUntil(signal)
  • merge(signal)
  • concat(signal)
  • startWith(initialValue)
  • zip(signal)
  • buffer(count)
  • bufferBy(signal)
  • delay(timeInterval)
  • throttle(timeInterval)
  • debounce(timeInterval)
• Class Methods
  • merge(signals)
  • merge2(signals) (generalized method for merge & combineLatest)
  • combineLatest(signals)
  • concat(signals)
  • zip(signals)

Helpers

• asSignal(ValueType) (WARNING: currently works for non-Optional only)
• Signal.once(value) (alias: just)
• Signal.never()
• Signal.fulfilled() (alias: empty)
• Signal.rejected() (alias: error)
• Signal(values:) (a.k.a Rx.fromArray)

Dependencies

• SwiftTask

References

• Introducing ReactKit // Speaker Deck (ver 0.3.0)

Licence

MIT