ReactiveCocoa is an Objective-C framework that uses Functional Reactive Programming principles. It provides APIs for composing and transforming streams of values over time. ReactiveCocoa defines streams as RACSignals (push-based) or RACSequences (pull-based) that produce events. It includes operators to manipulate streams, like map, filter, and combineLatest. This allows declarative programming by linking UI behavior to continuously updating data streams.

1. ReactiveCocoa
Werner Ramaekers
Jan Sabbe
Cocoaheads BE
12/03/2014

4. ReactiveCocoa (RAC)
is an Objective-C framework for
Functional Reactive
Programming.
It provides APIs for composing
and transforming streams of
values.

5. Whut ?

6. Programming
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Take inputs Produce outputs

7. Imperative programming
•int x; int y = 1; int z = 2;
•x = y + z; //x == 3; y == 1; z == 2;
!
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8. Imperative programming
•int x; int y = 1; int z = 2;
•x = y + z; //x == 3; y == 1; z == 2;
!
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•y = 2;
•NSLog(@“%i”, x); //-> ‘3’
!
# Input changed but output did NOT because it was
declared earlier….

9. Imperative programming
•int x; int y = 1; int z = 2;
•x = y + z; //x == 3; y == 1; z == 2;
!
PIN OUT
STATE•y = 2;
•NSLog(@“%i”, x); //-> ‘3’
!
# Input changed but output did NOT because it was
declared earlier….

10. Declaractive programming
•The developer describes the problem
domain in a declarative way,
!
•The focus is NOT on state
!
•Focus is on :
•data flow
•propagation of change

11. Functional Programming
•is one way of declarative programming.
!
•Functional programming..
•deemphasizes state & mutable data
•emphasizes functions that produce
outputs based on inputs : z = f(x, y)
PIN OUT

12. Reactive Programming
•also is a way of declarative
programming
!
•Reactive Programming ..
•dynamically links the program’s behaviour
to its continuously updating data stream
PIN OUT

13. Reactive Programming
•also is a way of declarative
programming
!
•Reactive Programming ..
•dynamically links the program’s behaviour
to its continuously updating data stream
PIN OUT
•E.g. : a spreadsheet application where
•cell A1 (= B1 + C1)

14. Functional Reactive Programming
•.. combines the FUNCTIONAL and
REACTIVE programming styles.
!
•.. links functions that observe
continuous and dynamic streams of
data (inputs) to the program’s
behaviour (outputs) in real time.

15. ReactiveCocoa (RAC)
is an Objective-C framework for
Functional Reactive
Programming.
It provides APIs for composing
and transforming streams of
values.

16. RAC : ReActiveCocoa
Stream Subscriber
RACStream produces a Stream existing of …

17. RAC : ReActiveCocoa
Stream
Next Event
Subscriber
RACStream produces a Stream existing of …

18. RAC : ReActiveCocoa
Stream
Next Event
Complete Event
Subscriber
RACStream produces a Stream existing of …

19. RAC : ReActiveCocoa
Stream
Next Event
Complete Event
Subscriber
Error Event
RACStream produces a Stream existing of …

20. RAC : ReActiveCocoa
Stream Subscriber
[ 1, 2, 3]
RACSequence

21. RAC : ReActiveCocoa
Stream Subscriber
[ 1, 2, 3]
123
RACSequence

22. RAC : ReActiveCocoa
Stream Subscriber
RACSignal
Client Server

23. RAC : ReActiveCocoa
Stream Subscriber…
JSON
RACSignal
Client Server

24. RAC : ReActiveCocoa
Stream Subscriber…
∞
RACSignal
Client
listen

25. RAC : ReActiveCocoa
RACStream
RACSignal RACSequence

26. ReactiveCocoa
•RACStream
•abstract class
•represents some sequential flow of data
•RACSignal (cold)
•push-driven data stream of future values
•cfr Network call
•must be subscribed to in order to access data
•RACSequence
•pull-driven data stream
•similar to Cocoa collection classes (NSArray, ..)
•but values are evaluated lazily - only when needed

27. Details please

28. RACSignal
!
[self.textField.rac_textSignal subscribeNext:^(id x) {
NSLog(@“New value : %@“, x);
} error:^(NSError *error){
NSLog(@“Error : %@“, error);
} completed:^{
NSLog(@“That’s all folks !”);
}];

29. RACSignal
!
[self.textField.rac_textSignal subscribeNext:^(id x) {
NSLog(@“New value : %@“, x);
!
!
!
!
}];

30. RACSignal : combineLatest
123
C.L.
( )=,

31. RACStream operators
•Simplifies transformations of streams into
new streams
•map, filter, fold/reduce
!

32. RACStream : map
MAP =
( ) =
RACSequence *stream = [@[@(1), @(2), @(3)] rac_sequence];
[stream map:^id(id value) {
return @(pow([value integerValue], 2));
}];
NSLog(@“%@“, [stream array]);

33. RACStream : flatten map
FMAP =
( ) =
Function result = stream

34. RACStream : filter
RACSequence *stream = [@[@(1), @(2), @(3)]; rac_sequence];
NSLog(@“%@“,
[[[array rac_sequence] filter:^BOOL(id value){
return [value integerValue] % 2 == 0;
}] array]
);
Filter =
( ) = True
?

36. Validating input the “old” way
#pragma mark - UITextFieldDelegate
!
- (BOOL) textField:(UITextField *)textField
shouldChangeCharactersInRange:(NSRange)range
replacementString:(NSString *)string
{
self.createButton.enabled = [self isFormValid];
!
return YES;
}

37. Validating input the “old” way
#pragma mark - UITextFieldDelegate
!
- (BOOL) textField:(UITextField *)textField
shouldChangeCharactersInRange:(NSRange)range
replacementString:(NSString *)string
{
self.createButton.enabled = [self isFormValid];
!
return YES;
}
- (BOOL)isFormValid {
return [self.usernameField.text length] > 0 &&
[self.emailField.text length] > 0 &&
[self.passwordField.text length] > 0 &&
[self.passwordField.text
isEqual:self.passwordVerificationField.text];
}
…
……
…

39. Validating input the “RAC” way
RAC(self.createButton, enabled) =
!
[RACSignal combineLatest:@[
self.usernameTF.rac_textSignal,
self.emailFieldTF.rac_textSignal,
self.passwordFieldTF.rac_textSignal,
self.passwordVerificationFieldTF.rac_textSignal
]
reduce:^(NSString *username,
NSString *email,
NSString *password,
NSString *passwordVerification) {
return @([username length] > 0 &&
[email length] > 0 &&
[password length] > 8 &&
[password isEqual:passwordVerification]);
}];

40. Validating input the “RAC” way
RAC(self.createButton, enabled) =
!
[RACSignal combineLatest:@[
self.usernameTF.rac_textSignal,
self.emailFieldTF.rac_textSignal,
self.passwordFieldTF.rac_textSignal,
self.passwordVerificationFieldTF.rac_textSignal
]
reduce:^(NSString *username,
NSString *email,
NSString *password,
NSString *passwordVerification) {
return @([username length] > 0 &&
[email length] > 0 &&
[password length] > 8 &&
[password isEqual:passwordVerification]);
}];

41. “not so fast cowboy .. “
•RAC(object, key path) is a macro
•creates a one-way binding
•ex. bind “enabled” property of a UIButton to a
signal

42. Now, show me a real app

43. Station locator app

44. Station locator app

45. Station locator app

46. Station locator app
Core Data
Stations
GPS coord
Services
Prices

47. Station locator app
Core Data
Stations
GPS coord
Services
Prices
Driving
distance

48. Station locator app
Prices.xml
Core Data
Stations
GPS coord
Services
Prices
Driving
distance

49. Station locator app
Stations.xml Prices.xml
Core Data
Stations
GPS coord
Services
Prices
Driving
distance

50. Easier asynchronous code
Driving
distance
1
2
3 Core Data lookup in Background
current location

51. RAC( ) = (51.2, 5.46)
station (id=4)
flattenMap
searchClosest(51.2,5.46)
flattenMap
getDrivingDistance(4)
JSON
map
JSON -> km
"4.5 km"

52. Sort stations by driving distance
station (id=1)
station (id=3)
station (id=2)
getDrivingDistance
combineLatest
sort [3,1,2]
fetching driving distances concurrently
when all available, sort

53. MVC

54. MVC

55. Scott,
how do we test
UIViewControllers

56. ViewModel pattern
ViewController
sets up binding
animations
ViewModel
(BOOL) shop
(BOOL) bread
(RACCommand) search
SearchService
(RACSignal)
searchWithCriteria
validates + delegate to service
do actual search

57. ViewModel pattern
ViewController
sets up binding
animations
ViewModel
(BOOL) shop
(BOOL) bread
(RACCommand) search
SearchService
(RACSignal)
searchWithCriteria
mock out the real search service
do search against in memory DB
easily testable
harder to test
hard to test but trivial

58. ViewModel pattern
ViewController
sets up binding
animations
ViewModel
(BOOL) shop
(BOOL) bread
(RACCommand) search
SearchService
(RACSignal)
searchWithCriteria
validates + delegate to service
do actual search
what is this?

59. RACCommand
while getting current location, searching stations, sort by driving distance,... show activity indicator
[[RACCommand alloc] initWithSignalBlock:^RACSignal *(id sender) {
return [self createSearchSignal];
}];
ViewModel

60. RACCommand
while getting current location, searching stations, sort by driving distance,... show activity indicator
[[RACCommand alloc] initWithSignalBlock:^RACSignal *(id sender) {
return [self createSearchSignal];
}];
ViewModel
ViewController
self.searchButton.rac_command = self.viewModel.searchCommand;
RAC(self, spinner.hidden) = [self.viewModel.searchCommand.executing not];

61. ReactiveCocoa …
•keeps the app focused on representing data
& UX
•can reduce complexity bc you don’t need to
worry about ‘state’ so much
•keeps related code close together (via
blocks)
•helps to make your code more testable (via
MVVM)

62. but ReactiveCocoa …
•introduces another way of thinking.
•adds another learning curve on top of
Cocoa
!
•is a framework by GitHub and not Apple
!
•will Apple "sherlock" ReactiveCocoa ?

63. One last thing

64. Thank you