1. ReactiveCocoa
joehsieh
2014/02/13

2. Outline
•
What is reactiveCocoa?
•
RAC basic components
•
MVVM

3. What is ReactiveCocoa?
•
ReactiveCocoa = Functional Reactive(Binding)
Programming

4. MVC
ViewController exists many glue code.

5. Cocoa Binding(Mac Only)
•
The Cocoa bindings technology provides a
means of keeping model and view values
synchronized without you having to write a lot of
“glue code.”(less glue code) It allows you to
establish a mediated connection between a view
and a piece of data, “binding” them such that a
change in one is reflected in the other(reactive).

6. Demo for Cocoa Binding

7. Binding for iOS?
•
Binding (Reactive) version(Mac Only) is based
on KVO, so we can also achieve binding by KVO
in iOS.

8. KVO Demo

9. RAC basic components

10. RACStream
•
It applies higher-oder functions to handle
incoming data (map, reduce, filter, ect…)
•
for binding values : RACSignal(Push-driven)
•
for collection : RACSequence(Pull-driven)

11. RACSignal
filter
subject
v
map
v
observer
!
•
value: nextValue, error or complete message.

12. KVO
[RACObserve(self, username) subscribeNext:^(NSString
*newName) {!
NSLog(@"%@", newName);!
}];

13. Chained Signal
[[RACObserve(self, username)!
filter:^(NSString *newName) {!
return [newName hasPrefix:@"j"];!
}]!
subscribeNext:^(NSString *newName) {!
NSLog(@"%@", newName);!
}];

14. Derive state
RAC(self, createEnabled) = [RACSignal !
combineLatest:@[ RACObserve(self, password),
RACObserve(self, passwordConfirmation) ] !
reduce:^(NSString *password, NSString *passwordConfirm) {
return @([passwordConfirm isEqualToString:password]);
}];

15. Trigged after a group of
operations completes
[[RACSignal !
merge:@[ [client fetchUserRepos], [client fetchOrgRepos] ]] !
subscribeCompleted:^{!
NSLog(@"They're both done!");!
}];

16. Solves callback hell
[[[[client !
logInUser] !
flattenMap:^(User *user) {!
// Return a signal that loads cached messages for the user.!
return [client loadCachedMessagesForUser:user];!
}]!
flattenMap:^(NSArray *messages) {!
// Return a signal that fetches any remaining messages.!
return [client fetchMessagesAfterMessage:messages.lastObject];!
}]!
subscribeNext:^(NSArray *newMessages) {!
NSLog(@"New messages: %@", newMessages);!
} completed:^{!
NSLog(@"Fetched all messages.");!
}];

17. Advantages
•
RAC is that it provides a single, unified
approach to dealing with asynchronous
behaviors, including delegate methods, callback
blocks, target-action mechanisms, notifications,
and KVO.

18. RACSequence
•
Adds higher-order functions to collection.
•
It is pull-driven(works on demand)

19. Imperative Programming
testData is an array from 1 to 100
NSMutableArray *result = [NSMutableArray
array];
for (NSNumber *i in testData) {
NSUInteger tempValue = @(pow([i intValue]
, 2));
if (tempValue % 2 == 0) {
[result addObject:@(tempValue)];
}
}

20. Functional Programming
RACSequence *sequence = [[[testData rac_sequence]
map:^id(id value) {
return @(pow([value intValue] , 2));
}] filter:^BOOL(id value) {
return ([value intValue] % 2 == 0);
}];
// evaluate sequence (pull data from sequence)
NSLog(@"%@", [sequence array]);

21. Demo

22. BMI Imperative

23. BMI RAC
height text
field
180cm
weight
text field
height
weight
75kg
combine
Input
BMIValue
label
23.15
BMIValue
Output
map
BMIStatus
label
Normal weight
green
BMIStaus
background
color

24. Refines BMI by MVVM
Separates presentation and validation logic from controller
to viewModel.

25. Benefits of MVVM
•
We can easily Unit Test the View Model
•
It’s easier to change the UI

26. Reference
•
http://elm-lang.org/learn/What-is-FRP.elm
•
http://blog.maybeapps.com/post/42894317939/input-and-output
•
https://github.com/ReactiveCocoa/ReactiveCocoa
•
http://www.teehanlax.com/blog/model-view-viewmodel-for-ios/
•
https://leanpub.com/iosfrp
•
http://blog.devtang.com/blog/2014/02/11/reactivecocoaintroduction/
•
http://github.com/joehsieh/RACBMIiOS <— here is my demo