EmitterKit wants to replace your NSNotification, key-value observation, and general event handling habits!

• Simpler syntax!
• Type safety with generic Event class!
• Built-in one-time listeners!
• Key-value observation for NSObjects!
• Has a Notification class for backwards-compatibility with NSNotificationCenter!
• Removes the need to call removeObserver() for NSNotifications!

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Installation

Not yet available on CocoaPods.

For now, add EmitterKit.xcodeproj as a submodule in your Xcode project and add EmitterKit.framework as a target dependency in your Build Phases. Then, add a Copy Files phase in your Build Phases to the Frameworks directory, and add EmitterKit.framework.

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Event

An Event emits data. Its generic parameter specifies what type of data it emits! This is awesome.

All listeners are removed when an Event is deallocated.

let didLogin = Event<User>()

didLogin.once { user in
  println("Successfully logged in as \(user.name)!")
}

didLogin.emit(user)

Event is a subclass of Emitter.

I tend to use Events as properties of my Swift classes, when it makes sense.

class MyScrollView : UIScrollView, UIScrollViewDelegate {
  let didScroll = Event<CGPoint>()
  
  override init () {
    super.init()
    delegate = self
  }
  
  func scrollViewDidScroll (scrollView: UIScrollView) {
    didScroll.emit(scrollView.contentOffset)
  }
}

Otherwise, I can use a target to associate an Event with a specific AnyObject. This is useful for classes I cannot add properties to, like UIView for example.

let myView = UIView()
let didTouch = Event<UITouch>()

didTouch.once(myView) {
  println("We have a winner! \($0)")
}

didTouch.emit(myView, touch)

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Signal

A Signal is essentially an Event that can't pass data. Convenient, huh?

This is a subclass of Emitter, too.

let didLogout = Signal()

didLogout.once {
  println("Logged out successfully... :(")
}

didLogout.emit()

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Notification

Notification wraps around NSNotification to provide backwards-compatibility with Apple's frameworks (e.g. UIKeyboardWillShowNotification) and third party frameworks.

Use it to create NotificationListeners that will remove themselves when deallocated. Now, you no longer have to call removeObserver() in your deinit phase!

You do not need to retain a Notification for your listener to work correctly. This is one reason why Notification does not subclass Emitter.

Notification(UIKeyboardWillShowNotification).once { data in
  println("keyboard showing. data: \(data)")
}

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Listener

A Listener represents a closure that will be executed when an Emitter emits.

When a Listener is constructed, it starts listening immediately.

Toggle on and off by setting the isListening: Bool property.

If a Listener's once: Bool property == true, it will stop listening after it executes once.

Important: Remember to retain a Listener if once == false! Make a [Listener] property and put it there.

var listeners = [Listener]()

// Retain that sucka
listeners += mySignal.on {
  println("beep")
}

// Single-use Listeners retain themselves ;)
mySignal.once {
  println("boop")
}

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Key-Value Observation

EmitterKit adds on(), once(), and removeListeners() instance methods to every NSObject.

let myView = UIView()
let myProperty = "layer.bounds" // supports dot-notation!

listeners += myView.on(myProperty) { 
  (values: Change<NSValue>) in
  println(values)
}

Check out the Change class to see what wonders it contains. It implements the Printable protocol for easy debugging!

The NSKeyValueObservingOptions you know and love are also supported! Valid values are .Old, .New, .Initial, .Prior, and nil. If you don't pass a value at all, it defaults to .Old | .New.

myView.once("backgroundColor", .Prior | .Old | .New) { 
  (change: Change<UIColor>) in
  println(change)
}

It runs on top of traditional KVO techniques, so everything works as expected!

WARNING: If you use these methods, you must call removeListeners(myListenerArray) before your NSObject deinits. Otherwise, your program will crash. I suggest making a subclass of UIView, overriding willMoveToWindow(), and putting removeListeners() in there. That's not always ideal if you're not working with a UIView, but that's all I use it for right now, so I can't help you in other cases.

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Crafted by Alec Larson @aleclarsoniv