An Introduction to Reactive Cocoa
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This document introduces Reactive Cocoa, a framework for Functional Reactive Programming in Objective-C. It describes Reactive Programming as a paradigm oriented around data flows and propagation of change. It explains the key concepts in Reactive Cocoa including streams (signals and sequences), how they allow declarative data transformations, and examples of using signals to react to user interface changes.
![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
}
}
}](https://image.slidesharecdn.com/anintroductiontoreactivecocoa-130729113255-phpapp02/85/An-Introduction-to-Reactive-Cocoa-7-320.jpg)
![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](https://image.slidesharecdn.com/anintroductiontoreactivecocoa-130729113255-phpapp02/85/An-Introduction-to-Reactive-Cocoa-8-320.jpg)
![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];
}];](https://image.slidesharecdn.com/anintroductiontoreactivecocoa-130729113255-phpapp02/85/An-Introduction-to-Reactive-Cocoa-11-320.jpg)
![Signal Example
[self.textField.rac_textSignal
subscribeNext:^(NSString *value) {
NSLog(@"Text field updated: %@",
value);
}];](https://image.slidesharecdn.com/anintroductiontoreactivecocoa-130729113255-phpapp02/85/An-Introduction-to-Reactive-Cocoa-13-320.jpg)
![Signal Example 2
[[self.textField.rac_textSignal
filter:^BOOL(NSString *value) {
return [value length] >= 3;
}]
subscribeNext:^(NSString *value) {
NSLog(@"Text field updated: %@",
value);
}];](https://image.slidesharecdn.com/anintroductiontoreactivecocoa-130729113255-phpapp02/85/An-Introduction-to-Reactive-Cocoa-14-320.jpg)
![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;](https://image.slidesharecdn.com/anintroductiontoreactivecocoa-130729113255-phpapp02/85/An-Introduction-to-Reactive-Cocoa-16-320.jpg)
![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;](https://image.slidesharecdn.com/anintroductiontoreactivecocoa-130729113255-phpapp02/85/An-Introduction-to-Reactive-Cocoa-17-320.jpg)
An Introduction to Reactive Cocoa
- 1. An Introduction to Reactive Cocoa Ara Hacopian BohConf July 2013
- 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;