Taking a peak at ReactiveCocoa 3.0 Cocoaheads Montreal 14/07/2015 

My twitter avatar shows me casually playing guitar. I got nice comments when I also used it on Facebook. 

I was actually warming up with a super-simple exercice. (Don't tell my mom, she was super-proud) 

I started taking lessons a few months ago, I have a great teacher but to be honest, I'm still not very good at it. ! 

This is pretty much the same with ReactiveCocoa. 

Me, Myself and ReactiveCocoa • I have been using it for a couple of years, on and off • I'm no expert, but I love the tech, the idea and the community • Ash Furrow said it was okay 

ReactiveCocoa, a history • OpenSourced by the fancy people at Github in 2012 • Used in Github for Mac, for example • A new version written in swift released (as a beta) a few month ago • (The history is not that important) 

What is ReactiveCocoa ? 

ReactiveCocoa is a framework used for composing and transforming sequences of values 

No seriously, what is it? 

I like to see ReactiveCocoa as a tool to send stuff through pipes 

Value → Different Value 

Sequence of Values → Different Values 

In ReactiveCocoa, you play with Signals - (RACSignal *)callWebservice { return [RACSignal createSignal:^RACDisposable *(id subscriber) { NSURLSessionDataTask *task = [self.session dataTaskWithURL: url completionHandler:^(...) { // ... }]; [task resume]; return [RACDisposable disposableWithBlock:^{ [task cancel]; }]; }]; } 

In ReactiveCocoa, you play with Signals NSArray *payload = [NSJSONSerialization JSONObjectWithData: data options: 0 error: nil]; // Some error handling would be nice ! [payload enumerateObjectsUsingBlock:^(NSDictionary *obj, NSUInteger idx, BOOL *stop) { [subscriber sendNext: obj]; }]; [subscriber sendCompleted]; 

In ReactiveCocoa, you play with Signals [[client callWebservice] map:^(NSDictionary *payload) { return [[FancyObject alloc] initWithDictionary: payload]; }]; 

ReactiveCocoa 2.0 fitted really well with Objective-C 

But things can rapidly get out of hands [[[[client logInUser] flattenMap:^(User *user) { return [client loadCachedMessagesForUser:user]; }] flattenMap:^(NSArray *messages) { return [client fetchMessagesAfterMessage:messages.lastObject]; }] subscribeNext:^(NSArray *newMessages) { NSLog(@"New messages: %@", newMessages); } completed:^{ NSLog(@"Fetched all messages."); }]; 

[[[[[[[[[[[ !!!!!!!! 

ReactiveCocoa and Swift • Rewrote from scratch to benefit from Swift awesomeness • Strong typing everywhere • Still in beta, use with caution 

Getting started with ReactiveCocoa 3.0 • Drop the framework available on Github directly in your project • Use Cocoapods • Use Carthage, which uses ReactiveCocoa internally :mindblown.gif: 

Simple example func tick() -> Signal { var count = 0 return Signal { sink in NSTimer.schedule(repeatInterval: 1.0) { timer in sendNext(sink, "tick #\(count++)") } return nil } } 

Simple example: observing the signal let signal = tick() signal.observe(next: { println($0) }) 

Simple example func fetchCharacterNames() -> SignalProducer { return SignalProducer { observable, disposable in let names = ["Buffy", "Angel", "Spike", "Xander"] for (_, name) in enumerate(names) { sendNext(observable, name) } sendCompleted(observable) } } 

Simple example: observing the signal let signal = fetchCharacterNames() signal.observe(next: { println($0) }) 

Transforming values: what you'd expect createSignalProducer().map({ name in return Character(name: name) }) 

WRONG! ReactiveCocoa 3.0 is a lot more "functional" and map is actually a function that returns a new signal public func map(transform: T -> U) -> Signal -> Signal { // ... } 

If this code makes you feel stupid, join the club and we'll all get matching tatoos 

Transforming values: using map let charactersSignal = createSignalProducer() let mappedSignal = map(charactersSignal, { Character(name: $0) }) mappedSignal.start(...) 

Invoking the power of the |> operator createSignalProducer() |> map({ Character(name: $0) }) • Coming from the F# language • Makes your code pretty • Confuses Xcode like nothing before 

More complex (and relevant) example: the Photos framework • Working on an application that uses the Photos framework • Retrieving the latest photos = callbacksoup 

More complex example: the Photos framework 1. Iterating over a list of albums 2. For each of these albums, request the assets 3. For each asset, request a UIImage (asynchronously) 

Step 1: Fetching albums func fetchCollections() -> SignalProducer { return SignalProducer { observer, disposable in let fetchOptions = PHFetchOptions() let collections = PHAssetCollection.fetchAssetCollectionsWithType(.SmartAlbum, subtype: .Any, options: fetchOptions) for index in 0..

Step 1: Fetching collections fetchCollections().start(next: { collection in println(“Collection = \(collection.localizedTitle)”) }) 

Step 2: Fetching assets in specific collection func fetchAssets(inCollection collection: PHAssetCollection) -> SignalProducer { return SignalProducer { observer, disposable in // We only want the images let assetsOptions = PHFetchOptions() assetsOptions.predicate = NSPredicate(format: “mediaType = %i”, PHAssetMediaType.Image.rawValue) let assets = PHAsset.fetchAssetsInAssetCollection(collection, options: assetsOptions) for assetIndex in 0..

Step 3: Fetching thumbnails func fetchImage(forAsset asset: PHAsset) -> SignalProducer { return SignalProducer { observer, disposable in let size = CGSize(width: asset.pixelWidth, height: asset.pixelHeight) PHImageManager.defaultManager().requestImageForAsset(asset, targetSize: size, contentMode: .AspectFit, options: PHImageRequestOptions(), resultHandler: { (image, infos) -> Void in sendNext(observer, image) sendCompleted(observer) }) } } 

Step 4: Merging all the things func fetchLatestScreenshot() -> SignalProducer { return fetchCollections() |> flatMap(.Merge, { collection in return fetchAssets(inCollection: collection) |> flatMap(.Latest, { asset in return fetchImage(forAsset: asset) }) }) } 

flatMap is a common concept in functional programing • Apply a function that returns a sequence for each element in the "pipe" • Here it applies a function to every collection and returns a sequence of assets 

Bonus: Filtering assets // ... fetchAssets(inCollection: collection) |> filter({ asset in let size = CGSize(width: asset.pixelWidth, height: asset.pixelHeight) return find(resolutions, size) != nil }) // ... 

Conclusion • ReactiveCocoa is a great tool, even if it sounds confusing your app can benefit from it • Xcode will be confused a lot, it makes the development suspensefull • There is a lot I haven't covered (observing properties...) • Questions? 

Thanks! 1. Picture by the awesome @Misszonzonnette 2. Simple tick example Shamelessly borrowed from http:// blog.scottlogic.com 3. We're hiring at Mirego!