ReactiveCocoa at MobiDevDay 2013

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ReactiveCocoa or: How I Learned to Stop Worrying and Learn FRP

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Abstraction

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Objective-C OOP #import @interface Person : NSObject @property (nonatomic, copy) NSString *name; - (void)say:(NSString *)message withExclaim:(BOOL)exclaim; @end @implementation Person - (void)say:(NSString *)message withExclaim:(BOOL)exclaim { if (exclaim) { message = [message uppercaseString]; } NSLog(@"%@", message); } @end

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Declarative Programming

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NSArray *array = @[@"foo", @"bar", @"baz"]; NSMutableArray *uppercaseArray = [NSMutableArray array]; for (int i = 0; i < array.count; i++ ) { uppercaseArray[i] = [array[i] uppercaseString]; } // uppercaseArray: @[ @"FOO", @"BAR", @"BAZ" ] id u = [@[@"foo", @"bar", @"baz"] map:^id(NSString *s) { return [s uppercaseString]; }]; // u: @[ @"FOO", @"BAR", @"BAZ" ] Describes how to compute Describes what to compute

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Declarative Programming = Good thing

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The State of Our Apps

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Lots of state Poor code locality Boilerplate

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Complexity

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Taps Keyboard events GPS events Web service responses … UI updates File on disk New DB record Web service request … INPUT w!r" I#p$% &#' O$%p$% by Josh Abernathy http://j.mp/joshaberio OUTPUT

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Is there a better abstraction?

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Reactive Programming “Programming around data flows and the propagation of change”

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a = 2 b = 2 c = a + b # c is 4 b = 3 # now what’s the value of c?

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Data types that represent a value over time

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Streams sequences of values over time Signals observable streams affords reaction to past, present, and future values

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a := 2 # signal b := 2 # signal c := a + b # signal binding # other signals b 2 3 c a + b 4 5 2 a 4 7 5 6 1

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ReactiveCocoa “A [Cocoa] framework for composing and transforming streams of values”

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KVO property UI events Network request Async work … Values over time https://speakerdeck.com/joshaber/reactivecocoa-for-a-better-world

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@interface RACSignal : RACStream [RACAble(self.username) subscribeNext:^(NSString *newName) { NSLog(@"%@", newName); }]; https://github.com/ReactiveCocoa/ReactiveCocoa/blob/master/README.md next completed error sending a single value done sending all values & successful sending values but terminated in error

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[self.textField.rac_textSignal subscribeNext:^(NSString *text) { NSLog(@"Incoming text signal: %@", text); }];

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[[self.textField.rac_textSignal map:^id(id text) { return [text stringByAppendingString:@" – map'd it"]; }] subscribeNext:^(NSString *text) { NSLog(@"Incoming text signal: %@", text); }];

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RACSignal *url = [[[[button rac_signalForControlEvents:UIControlEventTouchUpInside] map:^id(id _) { return NSString *s = [@[ [NSURL URLWithString:@"http://nutshell.com"], [NSURL URLWithString:@"http://google.com"], [NSURL URLWithString:@"http://wikipedia.org"], [NSURL URLWithString:@"http://apple.com"], [NSURL URLWithString:@"http://github.com/ReactiveCocoa/ReactiveCocoa"], ] aps_randomObject]; }] publish] autoconnect]; RACSignal *html = [[url flattenMap:^RACStream *(NSURL *url) { NSStringEncoding encoding = NSUTF8StringEncoding; return [NSString rac_readContentsOfURL:url usedEncoding:&encoding scheduler:[RACScheduler scheduler]; }] deliverOn:RACScheduler.mainThreadScheduler]; RAC(label, text) = [url map:^id(NSURL *u) { return u.absoluteString; }]; [webView rac_liftSelector:@selector(loadHTMLString:baseURL:) withObjects:html, url];

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field.enabled = NO; [worker doWorkWithCompletionBlock:^(id result, NSError *error) { field.enabled = YES; if (error) { /* handle error */ } else /* handle result */ }]; RACCommand *doWork = [worker doWorkAsCommand]; RAC(field, enabled) = [RACAble(doWork, executing) not]; // later, when we want to do the work // our UI pipes are plugged together so we don’t need to // worry about that [doWork execute:sender]; // handle result of doWork somewhere else where it matters … less imperative … more declarative

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Demo

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Reduce unnecessary state Better code locality Fluent interface Simple data structures Composing functions

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Thanks!

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Andrew Sardone twitter: @andrewa2 app.net: @andrewsardone github.com/andrewsardone github.com/ReactiveCocoa pinboard.in/u:andrewsardone/t:ReactiveCocoa github.com/andrewsardone/RACMobiDevDay nsbrief.com/81-justin-spahr-summers/ Input and Output – j.mp/joshaberio Reactive Extensions (Rx) – j.mp/reactiveextensions