ReactiveCocoa is a framework for building reactive applications using signals that emit events. It allows defining data flows where events are propagated through operations like map, filter, and flatten. Signals can represent UI controls, network requests, or other asynchronous events. This allows building reactive user interfaces where UI is updated automatically in response to data changes. Operations are chained fluently on signals to transform and combine events.

1. ReactiveCocoa made
Simple with Swift!
@ColinEberhardt
ShinobiControls

2. Tutorials

3. What is ReactiveCocoa?
• ReactiveCocoa is an open-source framework
created by the GitHub team
• Inspired by Functional Reactive Programming
(FRP)
• Changes the way in which we structure our
applications
• Inspired by Microsoft’s ReactiveExtensions (Rx)

4. Functional Reactive Programming
• Functional Programming
• First-class functions, passed as arguments
to other functions
• Reactive Programming
• Focusses on data flow
• Functional Programming + Reactive
Programming = FRP

5. FRP - WTF?
http://stackoverflow.com/questions/1028250/what-is-functional-reactive-programming

6. In my own words …
• Every line of code we write is executed in reaction
to an event
• But … these events all have different interfaces
• delegates, target-action, KVO, closures
• ReactiveCocoa provides a standard interface for all
events
• Allows us to define a higher level language
• Easier to test too!

7. Learn through play

8. Code
Build
Run
Explain!
Repeat

9. Get Reactive
let textSignal: RACSignal =
usernameTextField.rac_textSignal()
!
textSignal.subscribeNext {
(text: AnyObject!) -> Void in
let textString = text as String
println(textString)
}

10. Simplified with Swift
func subscribeNextAs<T>(nextClosure:(T) -> ()) -> () {
self.subscribeNext {
(next: AnyObject!) -> () in
let nextAsT = next! as T
nextClosure(nextAsT)
}
}
textSignal.subscribeNextAs {
(text: String) -> () in
println(text)
}

11. Signals!
• A signal emits events
• next
• error
• completed
• A signal can have none,
one or more subscribers
textSignal.subscribeNextAs({
(text: String) in
println(text)
}, error: { (error) in
// ...
}, completed: {
// ...
})

12. Events
Signals can emit none, one or more next
events, optionally followed by either an error or
completed
COMPLETED
NEXT NEXT ERROR
NEXT NEXT NEXT NEXT …
intervals do not
have to be
regular!

13. Signal all things
• Network request
• A single next, followed by a completed
• Large download
• Multiple next events, representing partial data,
followed by completed
• UI control
• An infinite stream of next events

14. Operations
• ReactiveCocoa allows you to perform
operations on signals
• map, filter, skip, take, throttle …
• These operations are entirely agnostic to the
source of the signal

15. filter
let textSignal: RACSignal = usernameTextField.rac_textSignal()
!
let filteredText = textSignal.filterAs {
(text: NSString) -> Bool in
return text.length > 3
}
!
filteredText.subscribeNextAs {
(text: String) in
println(text)
}
A filter is a ‘gate’, filtering-out events which do not
match the given condition

16. What exactly are events?
• What does a next event actually look like?
• Anything!
• Signals are an interface for handling
asynchronous events
• The event contents is context dependant

17. map
let textSignal: RACSignal = usernameTextField.rac_textSignal()
!
let textLength = textSignal.mapAs {
(text: NSString) -> NSNumber in
return text.length
}
!
textLength.subscribeNextAs {
(length: NSNumber) in
println(length)
}
Transforms each next event

18. Creating a pipeline
let textSignal: RACSignal =
usernameTextField.rac_textSignal()
!
let textLength = textSignal.mapAs {
(text: NSString) -> NSNumber in
return text.length
}
!
let filteredText = textLength.filterAs {
(number: NSNumber) -> Bool in
return number > 3
}
!
filteredText.subscribeNextAs {
(length: NSNumber) in
println(length)
}

19. Fluent syntax
usernameTextField.rac_textSignal()
.mapAs {
(text: NSString) -> NSNumber in
return text.length
}.filterAs {
(number: NSNumber) -> Bool in
return number > 3
}.subscribeNextAs {
(length: NSNumber) in
println(length)
}
Operations return RACSignal, allowing method
chaining

20. rac_textSignal()
.mapAs {
(text: NSString) -> NSNumber in
return text.length
}.filterAs {
(number: NSNumber) -> Bool in
return number > 3
}.subscribeNextAs {
(length: NSNumber) in
println(length)
}
Value->-3-
rac_textSIgnal- map-
filter- subscribeNext-
NSString- NSNumber-usernameTextField.

21. Valid text fields
let validUsernameSignal = usernameTextField.rac_textSignal()
.mapAs { (text: NSString) -> NSNumber in
return self.isValidUsername(text)
}
!
validUsernameSignal.mapAs {
(valid: NSNumber) -> UIColor in
return valid.boolValue ? UIColor.clearColor() : UIColor.yellowColor()
}.setKeyPath("backgroundColor", onObject: usernameTextField)
• Unfortunately we need to ‘box’ bool values.
• I am sure ReactiveSwift will fix this ;-)

22. More Swift Magic!
!!
RAC(usernameTextField, "backgroundColor") <<
validUsernameSignal.mapAs {
(valid: NSNumber) -> UIColor in
return valid.boolValue ? UIColor.clearColor() : UIColor.yellowColor()
}
http://napora.org/a-swift-reaction/

23. More Sweet Sweet Swift!
func validToBackground(valid: NSNumber) -> UIColor {
return valid.boolValue ? UIColor.clearColor() : UIColor.yellowColor()
}
!
func isValidText(validator:(String) -> Bool)(text: NSString) -> NSNumber {
return validator(text)
}
!
let validUsernameSignal = usernameTextField.rac_textSignal()
.mapAs(isValidText(isValidUsername))
.distinctUntilChanged()
!
RAC(usernameTextField, "backgroundColor") <<
validUsernameSignal.mapAs(validToBackground)

26. Login button enabled state
let signUpActiveSignal = RACSignalEx.combineLatestAs(
[validUsernameSignal, validPasswordSignal]) {
(validUsername: NSNumber, validPassword: NSNumber) -> NSNumber in
return validUsername && validPassword
}
!
signUpActiveSignal.subscribeNextAs {
(active: NSNumber) in
self.signInButton.enabled = active
}
Combines two signals into a new one

27. The pipeline
NSString- BOOL- UIColor-password-rac_
rac_textSIgnal- map- map- backgroundColor-
BOOL-
reduce- subscribeNext-
NSString- BOOL- UIColor-username-combineLatest:
textSIgnal- map- map- backgroundColor-

28. Reactive Button Click
signInButton.rac_signalForControlEvents(.TouchUpInside)
.subscribeNext {
(button) in
println("clicked")
}
Replaces target-action with a signal

29. Creating Signals
func signInSignal() -> RACSignal {
return RACSignal.createSignal {
(subscriber) -> RACDisposable! in
println("Sign-in initiated")
self.signInService.signInWithUsername(self.usernameTextField.text,
password: self.passwordTextField.text) {
(success) in
println("Sign-in completed")
subscriber.sendNext(success)
subscriber.sendCompleted()
}
return nil
}
}

30. Using the sign-in signal
signInButton.rac_signalForControlEvents(.TouchUpInside)
.map {
(any) -> RACSignal in
self.signInSignal()
}.subscribeNext {
(any) in
println(any)
}

31. Doing it right!
signInButton.rac_signalForControlEvents(.TouchUpInside)
.flattenMap {
(any) -> RACSignal in
self.signInSignal()
}.subscribeNext {
(any) in
println(any)
}
flattenMap subscribes to a signal, returning
the resultant events

32. Side-effects
signInButton.rac_signalForControlEvents(.TouchUpInside)
.doNext {
(any) in
self.signInButton.enabled = false;
}.flattenMap {
(any) -> RACSignal in
self.signInSignal()
}.subscribeNextAs {
(success: NSNumber) in
self.signInButton.enabled = true;
self.handleSignInResult(success.boolValue)
}
Side-effects receive next events, but cannot mutate them

33. Login pipeline
doNext1
signInSignal1
BOOL1
UIBu3on1 BOOL1
rac_signalForControlEvents11 fla3enMap1 subscribeNext1

34. ReactiveCocoa Made Simple
• A signal emits events
• next
• error
• completed
• A signal can have multiple subscribers
• Signals can emit multiple next events, optionally
followed by either an error or completed

35. Random
cool stuff!

37. [[[[[[[self requestAccessToTwitterSignal]
then:^RACSignal *{
@strongify(self)
return self.searchText.rac_textSignal;
}]
filter:^BOOL(NSString *text) {
@strongify(self)
return [self isValidSearchText:text];
}]
throttle:0.5]
flattenMap:^RACStream *(NSString *text) {
@strongify(self)
return [self signalForSearchWithText:text];
}]
deliverOn:[RACScheduler mainThreadScheduler]]
subscribeNext:^(NSDictionary *jsonSearchResult) {
NSArray *statuses = jsonSearchResult[@"statuses"];
NSArray *tweets = [statuses linq_select:^id(id tweet) {
return [RWTweet tweetWithStatus:tweet];
}];
[self.resultsViewController displayTweets:tweets];
} error:^(NSError *error) {
NSLog(@"An error occurred: %@", error);
}];

39. https://github.com/ColinEberhardt/ReactiveSwiftFlickrSearch

41. // a signal that emits events when visibility changes
let visibleStateChanged = RACObserve(self, "isVisible").skip(1)
!
// filtered into visible and hidden signals
let visibleSignal = visibleStateChanged.filter { $0.boolValue }
let hiddenSignal = visibleStateChanged.filter { !$0.boolValue }
!
// a signal that emits when an item has been visible for 1 second
let fetchMetadata = visibleSignal.delay(1).takeUntil(hiddenSignal)
!
fetchMetadata.subscribeNext {
(next: AnyObject!) -> () in
// fetch data
}

42. Resources
• https://github.com/ReactiveCocoa/ReactiveCocoa
• Read the Change Logs!
• My Stuff …
• http://www.raywenderlich.com/u/ColinEberhardt
• https://github.com/ColinEberhardt
• The code from this presentation
• https://github.com/ColinEberhardt/
SwiftReactivePlayground

43. ReactiveCocoa made
Simple with Swift!
@ColinEberhardt
ShinobiControls