An intro to Reactive Cocoa from SmartLogic's Ara Hacopian.

1. An Introduction to
Reactive Cocoa
Ara Hacopian
BohConf
July 2013

2. Ara Hacopian
www.smartlogic.io
twitter.com/ahacop
github.com/ahacop
SmartLogic

3. What is Reactive Cocoa?
RAC is an Objective-C framework for
Functional Reactive Programming

4. Reactive Programming?
A programming paradigm oriented around
data flows and propagation of change.

5. Imperative
int x, y = 1, z = 1;
x = y + z; // x = 2; y = 1; z = 1;
y = 3; // x = 2; y = 3; z = 1;
NSLog(@"%d", x); // "2"

6. Reactive
int x, y = 1, z = 1;
x = y + z; // x = 2; y = 1; z = 1;
y = 3; // x = 4; y = 3; z = 1;
NSLog(@"%d", x); // "4"

7. We have this: KVO
// In your viewDidLoad/awakeFromNib/init
[self addObserver:self
forKeyPath: @"someString"
options:NSKeyValueObservingOptionNew
context:&someStringChangeContext];
// In dealloc
[self removeObserver: self
forKeyPath: @"someString"
context:&someStringChangeContext];
// Elsewhere in your class
- (void)observeValueForKeyPath:( NSString *)keyPath
ofObject:( id)object
change:( NSDictionary *)change
context:( void *)context
{
if (context == &someStringChangeContext) {
if ([keyPath isEqualToString: @"someString"]) {
// Do a bunch of stuff here
}
}
}

8. Do it in RAC
[RACAble(self.someString) distinctUntilChanged]
subscribeNext:^(NSString *string) {
// Do a bunch of things here, just like you would with KVO
}];
Source: http://tonyarnold.me/post/reactivelessons

9. Streams
A series of object values.
● Accessed sequentially.
● Available immediately or in the future.
● Allow for declarative transforms
Two types:
1. Signals
2. Sequences

10. Sequence
A pull-driven stream.
● Lazily evaluated collections

11. Sequence Example
// words = @[ NSArray containing words ]
RACSequence *normalizedLongWords =
[[words.rac_sequence
filter:^ BOOL (NSString *word) {
return [word length] >= 10;
}]
map:^(NSString *word) {
return [word lowercaseString];
}];

12. Signal
A push-driven stream.
● Generally represents data that will be
delivered in the future.
● Values are sent on the signal
● Users subscribe to access values
3 types of events sent to subscribers:
1. Next - provides next value
2. Error
3. Completed

13. Signal Example
[self.textField.rac_textSignal
subscribeNext:^(NSString *value) {
NSLog(@"Text field updated: %@",
value);
}];

14. Signal Example 2
[[self.textField.rac_textSignal
filter:^BOOL(NSString *value) {
return [value length] >= 3;
}]
subscribeNext:^(NSString *value) {
NSLog(@"Text field updated: %@",
value);
}];

16. RACSignal *formValid = [RACSignal
combineLatest:@[
self.userNameField.rac_textSignal,
self.emailField.rac_textSignal,
self.confirmEmailField.rac_textSignal,
]
reduce:^(NSString *userName, NSString *email,
NSString *confirmEmail) {
return @(username.length > 0
&& email.length > 0
&& confirmEmail.length > 0
&& [email isEqualToString:confirmEmail]);
}];
RAC(self.createAccountBtn.enabled) = formValid;

17. RACCommand
self.loginCommand = [RACCommand command];
self.loginSignals = [self.loginCommand
addSignalBlock:^(id sender) {
return [client logIn];
}];
[self.loginSignals subscribeNext:^(RACSignal
*loginSignal) {
[loginSignal subscribeCompleted:^(id _) {
NSLog(@"Logged in successfully!");
}];
}];
self.loginBtn.rac_command = self.loginCommand;

18. Resources
https://github.com/ReactiveCocoa/ReactiveCocoa
https://pinboard.in/u:andrewsardone/t:ReactiveCocoa

19. Questions?
http://www.smartlogic.io
http://www.twitter.com/smartlogic
http://www.github.com/smartlogic
http://www.facebook.com/smartlogic