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#DroidConBos @ragdroid `Rxify` Presented By : Garima Jain @ragdroid A simple spell for complex RxJava operators

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Who?

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#DroidConBos @ragdroid `Rxify` is for? • Already working on RxJava - More to learn.

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#DroidConBos @ragdroid `Rxify` is for? • Already working on RxJava - More to learn. • Beginner - Time to start Rxifying your apps

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#DroidConBos @ragdroid `Rxify` is for? • Already working on RxJava - More to learn. • Beginner - Time to start Rxifying your apps • Pros - Talk will be fun!

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#DroidConBos @ragdroid `Rxify` is for? • Already working on RxJava - More to learn. • Beginner - Time to start Rxifying your apps • Pros - Talk will be fun! • Not Interested?

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#DroidConBos @ragdroid `Rxify` is for?

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What?

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#DroidConBos @ragdroid • `Rxify` - term signifies use of RxJava • RxJava makes our lives simpler. • Cast a spell (use an operator) and we are good to go. `Rxify`

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#DroidConBos @ragdroid • Reactive Extensions for JVM (Java Virtual Machine). • Observer pattern for sequences of data / events. RxJava

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#DroidConBos @ragdroid RxJava makes lives simpler • Never having to worry about : • Low-level Threading • Synchronisation • Background Processing

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Why?

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#DroidConBos @ragdroid RxJava operators at first glance

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#DroidConBos @ragdroid RxJava operators at first glance

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#DroidConBos @ragdroid RxJava operators at first glance • Complex • Hard to understand • Marble Diagrams? What!!

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“The Plan”

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The Plan • Basics • Spells • Complex Spells • Thread Travel

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The Plan • Basics • Spells ✦ map() ✦ flatmap() ✦ filter() • Complex Spells • Thread Travel

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The Plan • Basics • Spells • Complex Spells ✦ zip() ✦ concat() vs merge() ✦ buffer() ✦ debounce() ✦ flatmap() vs concatMap() vs switchMap() • Thread Travel

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The Plan • Basics • Spells • Complex Spells • Thread Travel ✦ subscribeOn() ✦ observeOn()

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Basics

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#DroidConBos @ragdroid • Observable produces items, • Subscriber consumes those items. • Observable calls : (Actions) • onNext() multiple times • followed by onComplete() • OR onError() Basics

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#DroidConBos @ragdroid • Operators : • manipulate items between producer and consumer. • Schedulers • Main Thread • Computation, IO (Background Thread) • Test Scheduler Basics

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#DroidConBos @ragdroid Observable Pattern Producer Consumer A B C items Observable emits Subscriber consumes

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#DroidConBos @ragdroid Just-ify Simple Observable String Hello World! Observable.just("Hello World!”); Observable time Hello World

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#DroidConBos @ragdroid A B C A B C Rx-ify String Array Simple Observable List source = Arrays.asList("A", "B", "C");
 Observable.fromIterable(source); Observable

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“Spells” operators

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“Map-io” map() operator

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#DroidConBos @ragdroid Map Transforms every element of a collection of items.

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#DroidConBos @ragdroid Map-io Observable Map Observable 1 2 3 10 20 30

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#DroidConBos @ragdroid Observable Map Observable.fromIterable(Arrays.asList(1, 2, 3))
 .map(integer -> integer * 10); Observable 1 2 3 10 20 30

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“FlatMap-um” flatMap() operator

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#DroidConBos @ragdroid FlatMap • Every element of a collection • To another collection of items • Combines them into a single collection.

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#DroidConBos @ragdroid FlatMap-um Observable FlatMap Observable Hello World How Are You? Hello World How Are You?

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#DroidConBos @ragdroid Observable FlatMap List source = Arrays.asList("Hello World", "How Are You");
 Observable.fromIterable(source)
 .flatMap(s -> Observable.fromIterable(
 Arrays.asList(s.split(" ")))); Observable Hello World How Are You? Hello World How Are You?

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“Filter-rum” filter() operator

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#DroidConBos @ragdroid Filter Filter the original collection to emit items that satisfy a condition.

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#DroidConBos @ragdroid Filter-rum Observable Filter Observable 1 2 3 1 4 5 6 3 5 7 7

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#DroidConBos @ragdroid Observable Filter Observable 1 2 3 1 4 5 6 3 5 getSourceObservable() .filter(integer -> integer % 2 == 1) 7 7

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“Comples spells” complex operators

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“Zip-pyosa” zip() operator

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#DroidConBos @ragdroid Zip • Combine multiple collections together • According to some function • Emit the result of each combination.

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#DroidConBos @ragdroid Zip Marble Diagram

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#DroidConBos @ragdroid Zip Marble Diagram Looks a little Overwhelming

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#DroidConBos @ragdroid Zip Marble Diagram Looks a little Overwhelming

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#DroidConBos @ragdroid Fictional Problem (Polyjuice Potion) • Hermione wants to prepare Polyjuice potion (P = R + H). * • She is waiting for task Ron (R) to bring FluxWeed. • She is waiting for task Harry (H) to bring hair. • Both tasks R and H are executing asynchronously. • Only after both R and H are completed then P can start. * ‘+’ is some complex function (brewing the Polyjuice in this case)

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#DroidConBos @ragdroid Zip-Yosa Observable Zip Observable FluxWeed CrabHair Polyjuice Potion Observable

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#DroidConBos @ragdroid Observable Zip Observable FluxWeed CrabHair Polyjuice Potion Observable 
 return Observable.zip( fluxWeedObservable, hairObservable,
 (fluxWeed, student) -> new PolyJuice(fluxWeed, student.getHair()) .prepare()) );

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#DroidConBos @ragdroid Observable Zip Observable FluxWeed CrabHair Polyjuice Potion Observable 
 return Observable.zip( fluxWeedObservable, hairObservable,
 (fluxWeed, student) -> new PolyJuice(fluxWeed, student.getHair()) .prepare()) );

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#DroidConBos @ragdroid Observable Zip Observable FluxWeed CrabHair Polyjuice Potion Observable 
 return Observable.zip( fluxWeedObservable, hairObservable,
 (fluxWeed, student) -> new PolyJuice(fluxWeed, student.getHair()) .prepare()) );

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#DroidConBos @ragdroid Observable Zip Observable FluxWeed CrabHair Polyjuice Potion Observable 
 return Observable.zip( fluxWeedObservable, hairObservable,
 (fluxWeed, student) -> new PolyJuice(fluxWeed, student.getHair()) .prepare()) );

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#DroidConBos @ragdroid Can you relate the Polyjuice Potion Problem to any coding problem?

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#DroidConBos @ragdroid Can you relate the Polyjuice Potion Problem to any coding problem? YES! When multiple API calls are executing simultaneously.

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“Concat-ify” concat() operator “Merge-os” merge() operator VS

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#DroidConBos @ragdroid Concat “Emit the emissions from two or more Observables without interleaving them” source “Combine multiple Observables into one by merging their emissions” source Merge

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#DroidConBos @ragdroid Concat Merge 1 2 3 4 8 9 1 2 3 4 8 9 1 2 3 4 8 9 1 2 3 4 8 9 Concat-ify Merge-os

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#DroidConBos @ragdroid Fictional Problem (Snape’s Assignment) • Professor Snape has requested all students to write an essay on werewolves. • The students who will turn in the essay first will get more points than the ones submitting later. • Students are divided into four house observables : • GryffindorObservable (G), • SlytherinObservable (S), • HufflepuffObservable (H) and • RavenclawObservable(R)).

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#DroidConBos @ragdroid Observable Snape’s Assignment - Submission R1 R2 H1 H2 Observable Observable G1 G2 S1 S2 Observable

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#DroidConBos @ragdroid Observable concatify() {
 Observable slytherinObservable = getObservable(House.SLYTHERIN);
 Observable huffleObervable = getObservable(House.HUFFLEPUFF);
 Observable ravenObservable = getObservable(House.RAVENCLAW);
 Observable gryffindorObservable = getObservable(House.GRYFFINDOR);
 return Observable.concat(
 slytherinObservable,
 huffleObervable,
 ravenObservable,
 gryffindorObservable);
 } Snape’s Assignment - Draco’s trick

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#DroidConBos @ragdroid Snape’s Assignment - Draco’s trick S1 S2 H1 H2 R1 R2 G1 G2 Concat-ify Observable R1 R2 H1 H2 Observable Observable G1 G2 S1 S2 Observable

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#DroidConBos @ragdroid Guess who is not so pleased?

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#DroidConBos @ragdroid Guess who is not so pleased? YES!

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#DroidConBos @ragdroid Guess who is not so pleased? YES! Poor Hermione

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#DroidConBos @ragdroid Observable mergeos() {
 Observable slytherinObservable = getObservable(House.SLYTHERIN);
 Observable huffleObervable = getObservable(House.HUFFLEPUFF);
 Observable ravenObservable = getObservable(House.RAVENCLAW);
 Observable gryffindorObservable = getObservable(House.GRYFFINDOR);
 return Observable.merge(
 slytherinObservable,
 huffleObervable,
 ravenObservable,
 gryffindorObservable);
 } Snape’s Assignment - Hermione’s fix

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#DroidConBos @ragdroid Snape’s Assignment - Hermione’s fix G1 S1 G2 R1 H1 S2 R2 H2 Merge-os Observable R1 R2 H1 H2 Observable Observable G1 G2 S1 S2 Observable

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#DroidConBos @ragdroid Snape’s Assignment - Hermione’s fix

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#DroidConBos @ragdroid • Hit the cache first • If data found return data • Else Network call Problem : Cache First Then Network

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#DroidConBos @ragdroid • Hit the cache first • If data found return data • Else Network call Problem : Cache First Then Network Concat-ify

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#DroidConBos @ragdroid • Hit the cache first • If data found return data • Else Network call Observable> cacheObservable = getLecturesFromCache();
 Observable> lecturesFromServer = getLecturesFromServer();
 return cacheObservable .concatWith(lecturesFromServer)
 .take(1); Problem : Cache First Then Network

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#DroidConBos @ragdroid Fictional Problem (The Battle) • Dumbledore’s army (Harry, Hermione, Ron and others) • Death Eaters (Lucius Malfoy, Bellatrix Lestrange and others) • Each team is casting lethal spells against the other team. • Dumbledore’s army is not as experienced as the Death Eaters. • Spells produced by Death Eaters is overwhelming the Dumbledore’s army (consumer).

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“Buffer-undum” buffer() operator

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#DroidConBos @ragdroid Buffer • Buffer small chunks of items • Instead of emitting one item at a time. • Emit chunks

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#DroidConBos @ragdroid Buffer-undum Buffer Observable 1 2 3 4 Observable 1 2 3 4

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#DroidConBos @ragdroid Observable Buffer Observable 1 2 3 4 1 2 getSpellsObservable()
 .buffer(2); //count 3 4

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#DroidConBos @ragdroid Buffer-undum Buffer LOSS-LESS Observable 1 2 3 4 Observable 1 2 3 4

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#DroidConBos @ragdroid Buffer Observable 1 2 3 4 Observable 1 2 3 4

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“Debounce-y” debounce() operator

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#DroidConBos @ragdroid Debounce Emit an item only when, some time has passed since it last emitted anything.

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#DroidConBos @ragdroid Debounce-y Debounce Observable 1 2 3 4 Observable 1 2 4

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#DroidConBos @ragdroid Observable 1 2 3 4 Observable 1 2 4 Debounce

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#DroidConBos @ragdroid Observable 1 2 3 4 Observable 1 2 4 LOSSY Debounce

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#DroidConBos @ragdroid Observable 1 2 3 4 Observable 1 2 4 PROBLEM SOLVED Debounce

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#DroidConBos @ragdroid Observable 1 2 3 4 Observable 1 2 4 getSpellsObservable()
 .debounce(300, TimeUnit.MILLISECONDS); Debounce

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#DroidConBos @ragdroid Problem : Optimize Network Traffic Track User Events using any analytics library.

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#DroidConBos @ragdroid Problem : Optimize Network Traffic Track User Events using any analytics library. Simple Approach Server request whenever an event occurs. Over chatty producer (User Events) Slow Consumer (Network Request)

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#DroidConBos @ragdroid Problem : Optimize Network Traffic Track User Events using any analytics library. Buffer-undum Buffer some events before making a network request. Buffer-undum

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#DroidConBos @ragdroid Problem : Optimize Network Traffic Track User Events using any analytics library. Buffer-undum Observable.just(new ArrayList())
 .buffer(3) // buffer count
 .flatMap(events -> Observable.just(new TrackRequest(events)));

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#DroidConBos @ragdroid Problem : Auto-Search AutoComplete Search Suggestions

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#DroidConBos @ragdroid Problem : Auto-Search AutoComplete Search Suggestions Simple Approach Server request whenever a character is typed Over chatty producer (User Input) Slow Consumer (Network Request)

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#DroidConBos @ragdroid AutoComplete Search Suggestions Debounce-y Make a network request only if user has stopped typing. Debounce-y Solution : Auto-Search

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#DroidConBos @ragdroid Solution : Subject

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#DroidConBos @ragdroid Solution : Subject Producer Consumer A B C items Observable emits Subscriber consumes

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#DroidConBos @ragdroid Solution : Subject Producer Consumer A B C items Subject emits Subscriber consumes subject.onNext()

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#DroidConBos @ragdroid Solution : Subject Producer Consumer A B C items Subject emits Subject consumes subject.onNext() subject.subscribe()

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#DroidConBos @ragdroid Solution : Subject Subject extends Observable implements Observer { }

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#DroidConBos @ragdroid Solution : Subject Subject extends Observable implements Observer { } AsyncSubject BehaviorSubject PublishSuject ReplaySubject

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#DroidConBos @ragdroid Solution : Subject Subject extends Observable implements Observer { } via-Hedwig We are going to use a PublishSubject for this purpose.

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#DroidConBos @ragdroid Solution : Subject Subject extends Observable implements Observer { } via-Hedwig PublishSubject : once you subscribe, you get all the subsequent items.

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#DroidConBos @ragdroid AutoComplete Search Suggestions Debounce-y publishSubject
 .debounce(300, TimeUnit.MILLISECONDS)
 .flatMap(new Function>>() {
 @Override
 public ObservableSource> apply(String searchTerm) {
 return dataSource.getBook(searchTerm);
 }
 }) Solution : Auto-Search

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#DroidConBos @ragdroid Observable B Book Solution : Auto-Search Debounce-y String B Book Boo Bo x x

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#DroidConBos @ragdroid AutoComplete Search Suggestions Debounce-y Solution : Auto-Search publishSubject
 .debounce(300, TimeUnit.MILLISECONDS)
 .flatMap(new Function>>() {
 @Override
 public ObservableSource> apply(String searchTerm) {
 return dataSource.getBook(searchTerm);
 }
 })

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#DroidConBos @ragdroid Observable > flatMap-um Observable B Solution : Auto-Search (FlatMap) List1 List2 Book

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#DroidConBos @ragdroid Observable > Observable B Solution : Auto-Search (FlatMap) List1 Nice & Good! List2 Book

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#DroidConBos @ragdroid Observable > Observable B Solution : Auto-Search (FlatMap) What if Response (“Book) arrived before Response(“B”)? Book

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#DroidConBos @ragdroid Observable > List1 List2 flatMap-um Observable B Book Solution : Auto-Search (FlatMap) 1000ms 200ms

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#DroidConBos @ragdroid Solution : Auto-Search

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#DroidConBos @ragdroid Solution : Auto-Search (FlatMap)

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“ConcatMap-pum” concatMap() operator

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#DroidConBos @ragdroid ConcatMap • Just like flatMap(), but … • Concatenates rather than merges

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#DroidConBos @ragdroid Observable > List1 List2 flatMap-um Observable B Book Solution : Auto-Search (FlatMap) 1000ms 200ms

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#DroidConBos @ragdroid Observable > List1 concatMap-um Observable B Book Solution : Auto-Search (ConcatMap) 1000ms 200ms

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#DroidConBos @ragdroid Observable > List1 concatMap-um Observable B Book Solution : Auto-Search (ConcatMap) 1000ms 200ms S U B S C R I B E

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#DroidConBos @ragdroid Observable > List1 concatMap-um Observable B Solution : Auto-Search (ConcatMap) 1000ms Book 200ms List2

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#DroidConBos @ragdroid Solution : Auto-Search (ConcatMap)

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#DroidConBos @ragdroid Solution : Auto-Search (ConcatMap) TOO SLOW!

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“SwitchMap-pum” switchMap() operator

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#DroidConBos @ragdroid SwitchMap • Just like flatMap(), but … • Unsubscribe to previous observable • When new item emitted

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#DroidConBos @ragdroid SwitchMap Do not think of “SwitchMap” as switch() {case: }

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#DroidConBos @ragdroid SwitchMap Think of it as switchTo(newObservable)

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#DroidConBos @ragdroid SwitchMap It was earlier called flatMapLatest()

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#DroidConBos @ragdroid Observable > List1 List2 flatMap-um Observable B Book Solution : Auto-Search (FlatMap) 1000ms 200ms

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#DroidConBos @ragdroid Observable > List1 List2 switchMap-um Observable B Book Solution : Auto-Search (SwitchMap) 1000ms 200ms

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#DroidConBos @ragdroid Observable > List2 switchMap-um Observable B Book Solution : Auto-Search (SwitchMap) 200ms UNSUBSCRIBE

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#DroidConBos @ragdroid Solution : Auto-Search (SwitchMap)

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#DroidConBos @ragdroid Solution : Auto-Search (SwitchMap) ALL SET!

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“Thread Travel” with RxJava

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#DroidConBos @ragdroid Thread It’s a thread of execution in a program.

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#DroidConBos @ragdroid Schedulers For introducing multi-threading.

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#DroidConBos @ragdroid Schedulers • Schedulers.computation() - for computational work • Schedulers.io() - for IO-bound work • AndroidSchedulers.mainThread() - executes actions on Android main thread • new TestScheduler() - intended for testing purposes

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#DroidConBos @ragdroid • A new Thread is like a parallel universe • We all live in the main thread • Switching a thread - opening a portal to another dimension Fictional Threading

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#DroidConBos @ragdroid • Hermione is always eager to gain knowledge. • Two lectures are going on at the same time. • She is stuck in the dilemma of how to attend both the lectures. Fictional Problem (Hermione’s Time Turner)

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#DroidConBos @ragdroid • Hermione is always eager to gain knowledge. • Two lectures are going on at the same time. • She is stuck in the dilemma of how to attend both the lectures. Fictional Problem (Hermione’s Time Turner) via-Hedwig Time Turner allows hermione travel back in time

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“Expecto-SubscribeOn” subscribeOn() operator

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#DroidConBos @ragdroid SubscribeOn “specify the Scheduler on which an Observable will operate”

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#DroidConBos @ragdroid SubscribeOn • Specify the Starting Scheduler • Switch threads

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#DroidConBos @ragdroid SubscribeOn Start the magic

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“Observe-ate” observeOn() operator

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#DroidConBos @ragdroid ObserveOn • True magic of thread travel • Switch threads

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#DroidConBos @ragdroid ObserveOn • True magic of thread travel • Switch threads via-Hedwig Potterly speaking, observe-ate can open portals to different dimensions

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#DroidConBos @ragdroid Main Dimension Hermione’s Time Turner : Solution Main Thread

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#DroidConBos @ragdroid Expecto-subscribeOn Background Main Thread Hermione’s Time Turner : Solution

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#DroidConBos @ragdroid Expecto-subscribeOn Task Started Background Thread Hermione’s Time Turner : Solution ⌛ Main Thread

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#DroidConBos @ragdroid Expecto-subscribeOn observe-ate Task Started Task Completed Hermione’s Time Turner : Solution Main Thread Background Thread

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#DroidConBos @ragdroid Expecto-subscribeOn observe-ate Task Started Task Completed Hermione’s Time Turner : Solution Main Thread Background Thread

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#DroidConBos @ragdroid Hermione’s Time Turner : Solution Observable.defer(new Callable>() {
 @Override
 public ObservableSource call() {
 return Observable.just(new Lecture(id)) .delay(id, TimeUnit.SECONDS);
 }
 }); getLectureObservable()

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#DroidConBos @ragdroid Hermione’s Time Turner : Solution lectureOneObservable = getLectureObservable(1)
 .subscribeOn(AndroidSchedulers.mainThread())
 .observeOn(AndroidSchedulers.mainThread())
 .doOnNext(lecture -> {
 if (getView() != null) {
 getView().append("Attended Lecture " + lecture.getId());
 }
 });

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#DroidConBos @ragdroid Hermione’s Time Turner : Solution lectureTwoObservable = getLectureObservable(2)
 .subscribeOn(Schedulers.io())
 .observeOn(AndroidSchedulers.mainThread())
 .doOnNext(lecture -> {
 if (getView() != null) {
 getView().append("Attended Lecture " + lecture.getId());
 }
 });

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#DroidConBos @ragdroid Hermione’s Time Turner : Solution 
 Observable.zip(lectureOneObservable, lectureTwoObservable,
 (lecture, lecture2) -> String.format("Attended Lectures %s and %s", lecture.getId(), lecture2.getId()))
 .subscribe(message -> {
 if (getView() != null) {
 getView().append(message);
 }
 }); Zip the two

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#DroidConBos @ragdroid Hermione’s Time Turner : Action

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#DroidConBos @ragdroid • Learn by practice • Make RxJava your friend and not a foe • Learn by examples - Kaushik Gopal RxJava https://github.com/kaushikgopal/RxJava-Android-Samples • Have a look at the source code of demo app https://github.com/ragdroid/rxify • Slides at speakerdeck https://speakerdeck.com/ragdroid/rxify-a-simple-spell-for-complex-rxjava-operators-1 • My Medium blogs for more details https://medium.com/@ragdroid What’s Next

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#DroidConBos @ragdroid Acknowledgements via-Hedwig - Android community - Vikas @vickyturtle - Julien - Fueled - Ritesh @_Riteshhh - Droidcon Boston team

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#DroidConBos @ragdroid Acknowledgements via-Hedwig The terms lossy and lossless have been inspired from the post here.

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#DroidConBos @ragdroid Acknowledgements via-Hedwig Technical Definitions have been taken from website. http://reactivex.io/documentation/operators.html

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#DroidConBos @ragdroid Acknowledgements via-Hedwig Response on medium article from Paul Woitaschek : https://medium.com/@woitaschek/its-better-to-use-switchmap- as-you-don-t-care-about-old-results-315029110c75

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#DroidConBos @ragdroid Acknowledgements via-Hedwig Gifs have been taken from giphy.com.

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#DroidConBos @ragdroid Thank You

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FUELED http://fueled.com [email protected] +1.800.962.4587 568 Broadway, 11th Flr. New York, NY 10012 Questions?