ReactiveCocoa. Marc Prud'hommeaux Ottawa CocoaHeads February 13th, 2014

Transcription

1 ReactiveCocoa Marc Prud'hommeaux Ottawa CocoaHeads February 13th, 2014

2 Introduction

3 ReactiveCocoa Functional Reactive Programming Open-source library by Josh Abernathy & Justin Spahr-Summers of GitHub Modeled on Microsoft's Reactive Extensions for.net

4 Features The ability to compose operations on future data. An approach to minimize state and mutability. A declarative way to define behaviors and the relationships between properties. A unified, high-level interface for asynchronous operations. An API on top of KVO

5 State Changes are Signals Anyone can "subscribe" to a "signal" A signal can be: Tapping a UIButton Receiving data on a NSURLConnection A global event in NSNotificationCenter... and any other future state change

6 Features (summary) Less Spaghetti

7 Functional Reactive Programming First suggested in ICFP 97 paper Functional Reactive Animation by Conal Elliott and Paul Hudak.

8 Haskell 101

9 Coding, Observing, & Binding

10 Background: Key-Value Coding Key-Value Coding (KVC) "itemprice" productmodel.itemprice

11 Background: Key-Value Product : (strong) NSString Product *product = [[Product alloc] init]; [product setitemprice:10.0]; NSAssert([product itemprice] == via setter"); product.itemprice += 5.0; NSAssert(product.itemPrice == via property"); [product setvalue:@25.0 forkey:@"itemprice"]; NSAssert([[product valueforkey:@"itemprice"]

12 Background: Key-Value Observing Key-Value Observing (KVO) - (void)itempricedidchange Key-Value Coding (KVC) "itemprice" productmodel.itemprice

13 @interface TraditionalObserver : (weak) Product TraditionalObserver - (id)initwithproduct:(product *)product { if (self = [super init]) { self.observee = product; [product addobserver:self forkeypath:@"itemtitle" options:0 context:null]; [product addobserver:self forkeypath:@"itemprice" options:0 context:null]; } return self; } - (void)dealloc { [self.observee removeobserver:self forkeypath:@"itemtitle"]; [self.observee removeobserver:self forkeypath:@"itemprice"]; } - (void)observevalueforkeypath:(nsstring *)keypath ofobject:(id)object change: (NSDictionary *)change context:(void *)context { NSAssert(object == observee"); self.changecount++; // remember how many changes take place if ([keypath isequaltostring:@"itemtitle"]) [self titledidchange]; if ([keypath isequaltostring:@"itemprice"]) [self pricedidchange];

14 Traditional Key-Value Product : (strong) NSString TraditionalObserver : (weak) Product int Product *p = [[Product alloc] init]; TraditionalObserver *observer = [[TraditionalObserver alloc] initwithproduct:p]; NSAssert(observer.changeCount == change tracking"); p.itemtitle p.itemprice = 0.99; NSAssert(observer.changeCount == change tracking");

15 Reactive Subscription #import Product : (strong) NSString TraditionalObserver : (weak) Product int Product *product = [[Product alloc] init]; NSUInteger block pricechangecount = 0; [RACObserve(product, itemprice) subscribenext:^(nsnumber *newprice) { pricechangecount++; }]; NSAssert(priceChangeCount == change tracking (initial)"); product.itemprice = 9.99; NSAssert(priceChangeCount == change tracking (next value)");

16 RACObserve Macro Expanded Product *product = [[Product alloc] init]; NSUInteger block pricechangecount = 0; [RACObserve(product, itemprice) subscribenext:^(nsnumber *newprice) { pricechangecount++; }]; RACSignal *pricesignal = [product rac_valuesforkeypath:@"itemprice" observer:self]; [pricesignal subscribenext:^(nsnumber *newprice) { pricechangecount++; }]; NSAssert(priceChangeCount == change tracking"); product.itemprice = 9.99; NSAssert(priceChangeCount == change tracking");

17 Background: Cocoa Bindings Cocoa Bindings pricefield.text productmodel.price Key-Value Observing (KVO) - (void)itempricedidchange Key-Value Coding (KVC) "itemprice" productmodel.itemprice

18 Cocoa Product : (strong) NSString ProductViewController : (strong) IBOutlet NSTextField Product *product = [[Product alloc] init]; ProductViewController *controller = [[ProductViewController alloc] init]; NSTextField *field = controller.titlefield; [field bind:nsvaluebinding toobject:product withkeypath:@"itemtitle" options:nil]; product.itemtitle NSAssert([field.stringValue name"); product.itemtitle NSAssert([field.stringValue name");

19 ReactiveCocoa Product : (strong) NSString ProductViewController : (strong) IBOutlet NSTextField Product *product = [[Product alloc] init]; UITextField *textfield = [[UITextField alloc] init]; RACChannelTo(textField, text) = RACChannelTo(product, itemtitle); product.itemtitle NSAssert([[textField text] view"); textfield.text Paper"; NSAssert([product.itemTitle isequaltostring:@"flappy model");

20 RACChannelTo Macro Expanded Product *product = [[Product alloc] init]; UITextField *textfield = [[UITextField alloc] init]; RACChannelTo(textField, text) = RACChannelTo(product, itemtitle); RACKVOChannel *viewchannel = [[RACKVOChannel alloc] initwithtarget:textfield keypath:@"text" nilvalue:nil]; RACKVOChannel *modelchannel = [[RACKVOChannel alloc] initwithtarget:product keypath:@"itemtitle" nilvalue:nil]; viewchannel[@"followingterminal"] = modelchannel[@"followingterminal"]; product.itemtitle NSAssert([[textField text] view"); textfield.text Paper Tweet Saga++ by Fifty-Four Ltd."; NSAssert([product.itemTitle isequaltostring:@"flappy Paper Tweet Saga++ by Fifty- Four model");

21 Cocoa Bindings vs. ReactiveCocoa No ios support No block support Cumbersome value transformation No signal coalescing Difficult to debug Interface Builder

22 User Interface & Commands

23 ReactiveCocoa UI mechanisms Categories & Blocks

24 Commands UIButton *button = [UIButton buttonwithtype:uibuttontyperoundedrect]; [button addtarget:self action:@selector(buttonpressed:) forcontrolevents:uicontroleventtouchupinside]; - (IBAction)buttonPressed:(id)sender { // do something }

25 Commands UIButton *button = [UIButton buttonwithtype:uibuttontyperoundedrect]; button.rac_command = [[RACCommand alloc] initwithsignalblock:^(id _) { // do something return [RACSignal empty]; }];

26 UI Complexity Reduction Delegate Pattern: - (BOOL)isFormValid { return [self.usernamefield.text length] > 0 && [self. field.text length] > 0 && [self.passwordfield.text length] > 0 && [self.passwordfield.text isequal:self.passwordverificationfield.text]; } #pragma mark - UITextFieldDelegate - (BOOL)textField:(UITextField *)textfield shouldchangecharactersinrange:(nsrange)range replacementstring:(nsstring *)string { self.createbutton.enabled = [self isformvalid]; return YES; } Sample from

27 UI Complexity Reduction Reactive Pattern: RACSignal *formvalid = [RACSignal combinelatest:@[ self.username.rac_textsignal, self. field.rac_textsignal, self.passwordfield.rac_textsignal, self.passwordverificationfield.rac_textsignal ] reduce:^(nsstring *name, NSString * , NSString *pw1, NSString *pw2) { && .length && pw1.length > 8 && [pw1 isequal:pw2]); }]; RAC(self.createButton.enabled) = formvalid; Sample from

28 Model-View-ViewModel

29 Collections & Sequences

30 NSArray Filter & Map NSArray ]; NSArray *shortuppercasecolors = [[values filteredarrayusingpredicate: [NSPredicate predicatewithblock:^bool(nsstring *color, NSDictionary *bindings) { return [color length] <= 4; }]] valueforkeypath:@"uppercasestring"];

31 RACSequence Filter & Map NSArray ]; RACSequence *seq = [[values.rac_sequence filter:^bool(nsstring *color) { return [color length] <= 5; }] map:^id(nsstring *color) { return [color uppercasestring]; }]; NSAssert(([[seq Sequences are evaluated lazily

32 ReactiveCocoa Class Hierarchy RACStream RACSignal RACSequence RACChannelTerminal RACSubject RACChannel

33 Resources reactive-cocoa