RxJava Training

These are the slides from a two-day RxJava workshop we did for a group of Java-developers. RxJava is introduced with simple pictures and concepts for people who never worked with it before. In the second part of the workshop, we dive into more advanced concepts.

Transcript

1. RxJava: Functional Reactive Programming mit Java Malte Bucksch 1
2. Training Agenda • Part 1: RxJava Background and Overview • Part 2: RxJava Basics • Part 3: RxJava Operators • Part 4: Example of a modern UI architecture with RxJava • Part 5: Testing with RxJava • Part 6: RxJava Advanced Malte Bucksch 2
3. Goal of the training: You are ready to write software with RxJava Malte Bucksch 3
4. Stefan Kofler & Malte Bucksch 4
5. Vorstellungsrunde Stefan Kofler & Malte Bucksch 5
6. Terminology Malte Bucksch 6 Hacking Live-Coding
7. Questions are always more than welcome ! Malte Bucksch 7
8. Training Agenda • Part 1: RxJava Background and Overview • Part 2: RxJava Basics • Part 3: RxJava Operators • Part 4: Example of a modern UI architecture with RxJava • Part 5: Testing with RxJava • Part 6: RxJava Advanced Malte Bucksch 8
9. Part 1: Rx(Java) Background and Overview 1. Problem 2. What is Functional Reactive Programming (FRP)? 3. Why RxJava? 4. RxJava Basics 5. Exercise Malte Bucksch 9
10. Problem: Handling asynchronous data Malte Bucksch 10
11. Fetching search results button.setOnClickListener(view -> ); Malte Bucksch 11
12. Fetching search results button.setOnClickListener(view -> networkClient.fetchSearchResults(query, (results, error) -> { }) ); Malte Bucksch 12
13. Fetching search results button.setOnClickListener(view -> networkClient.fetchSearchResults(query, (results, error) -> { if (error != null) showError(error); else showResults(results); }) ); Malte Bucksch 13
14. Fetching search results button.setOnClickListener(view -> { new Thread(() -> networkClient.fetchSearchResults(query, (results, error) -> { if (error != null) showError(error); else showResults(results); }) ).start(); }); Malte Bucksch 14
15. Fetching search results button.setOnClickListener(view -> { new Thread(() -> networkClient.fetchSearchResults(query, (results, error) -> { runOnUiThread(() -> { if (error != null) showError(error); else showResults(results); }); }) ).start(); }); Malte Bucksch 15
16. One solution: Reactive data streams Malte Bucksch 16
17. Fetching search results RxView.clicks(button) Malte Bucksch 17
18. Fetching search results RxView.clicks(button) .flatMap(view -> networkClient.fetchSearchResults(query)) Malte Bucksch 18
19. Fetching search results RxView.clicks(button) .flatMap(view -> networkClient.fetchSearchResults(query)) .subscribe(this::showResults, this::showError); Malte Bucksch 19
20. Fetching search results RxView.clicks(button) .flatMap(view -> networkClient.fetchSearchResults(query)) .subscribeOn(Schedulers.newThread()) .subscribe(this::showResults, this::showError); Malte Bucksch 20
21. Fetching search results RxView.clicks(button) .flatMap(view -> networkClient.fetchSearchResults(query)) .subscribeOn(Schedulers.newThread()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(this::showResults, this::showError); Malte Bucksch 21
22. Stream for data in Motion – Example: Email input Malte Bucksch 22
23. Stream for data in Motion – Example: Email input Malte Bucksch 23 Filter (isEmailValid) Map (firstEmailPart) Subscriber Keyboard Input malte@quickbirdstudios.com malte “name@google.com”  “name” test 1234
24. History Lesson • ReactiveX developed by Microsoft (2010) • First Rx Extensions library: Rx.NET • Jafar Husain (Microsoft) switched to Netflix • Evangalized Rx • Wanted to simplify threading • Netflix published RxJava (2013) • RxJava found its way from servers to clients Malte Bucksch 24 Erik Meijer, 2010
25. Was ist Functional Reactive Programming? Functional programming + Reactive programming Malte Bucksch 25
26. Was ist Functional Reactive Programming? Functional programming + Reactive programming Malte Bucksch 26
27. Functional programming f(input) = output • Everything is a mathematic function • Result of function depends ONLY on the input Malte Bucksch 27 Code becomes more predictable
28. Stream for data in Motion – Example: Email input Malte Bucksch 28 Filter (isEmailValid) Map (firstEmailPart) Subscriber Keyboard Input tom@gmail.com tom test 1234
29. Functional programming: Streams f(input) = output Malte Bucksch 29
30. Functional programming: Streams f([“test”,”1234”,”tom@gmail.com”]) = output Malte Bucksch 30
31. Functional programming: Streams f([“test”,”1234”,”tom@gmail.com”]) = tom Malte Bucksch 31
32. Functional programming: Streams stripEmail([“test”,”1234”,”tom@gmail.com”]) = tom Malte Bucksch 32
33. Was ist Functional Reactive Programming? Functional programming + Reactive programming Malte Bucksch 33
34. Example: Imperative programming b = 1 c = 1 a := b + c // a = 2 c = 2 // a = 2 Malte Bucksch 34 Does NOT change when b or c change
35. Example: Reactive programming b = 1 c = 1 a := b + c // a = 2 c = 2 // a = 3 Malte Bucksch 35 DOES change when b or c change
36. Everything is a Stream Malte Bucksch 36 UI events Network requests Database Operations Processing operations
37. It’s like an excel document Malte Bucksch 37 Functional Reactive
38. Was ist Functional Reactive Programming? Functional programming + Reactive programming Malte Bucksch 38
39. What is RxJava? API for asynchronous programming with observable streams Malte Bucksch 39
40. What is ReactiveX? Malte Bucksch 40 RxJava, RxJS, Rx.NET, RxScala, RxClojure, RxSwift …
41. ReactiveX Malte Bucksch 41 Streams Operators Subscriptions
42. Rx is cross-platform • Target area • Front end • Back end • Programming languages • RxJava • RxSwift • RxKotlin • RxJS • … Malte Bucksch 42
43. Why Rx? • Conciseness • Fluent interface • Lazy evaluation • Easy concurrency • Async Error Handling Malte Bucksch 43
44. Malte Bucksch 44
45. RxJava Basics Malte Bucksch 45
46. Double Clicks Malte Bucksch 46
47. Double clicks with RxJava Malte Bucksch 47 Observable<Object> clicks = RxView.clicks(button);
48. Double clicks with RxJava Malte Bucksch 48 Observable<Object> clicks = RxView.clicks(button); clicks.buffer(clicks.debounce(1, TimeUnit.SECONDS)) …
49. Double clicks with RxJava Malte Bucksch 49 Observable<Object> clicks = RxView.clicks(button); clicks.buffer(clicks.debounce(1, TimeUnit.SECONDS)) .filter(list -> list.size() == 2) …
50. Double clicks with RxJava Malte Bucksch 50 Observable<Object> clicks = RxView.clicks(button); clicks.buffer(clicks.debounce(1, TimeUnit.SECONDS)) .filter(list -> list.size() == 2) .subscribe(size -> System.out.println("Double click!"));
51. Double clicks: Imperative style Malte Bucksch 51 button.setOnClickListener(v -> { … });
52. Double clicks: Imperative style Malte Bucksch 52 private long lastClickTime = 0; … button.setOnClickListener(v -> { long clickTime = System.currentTimeMillis(); if (clickTime - lastClickTime < 1000) { System.out.println("Double click!"); lastClickTime = 0; } else { lastClickTime = clickTime; } });
53. Pull Malte Bucksch 53 Push
54. Pull vs. Push Pull-based (Imperative Programming) • You pull the data once you decided that you need it • You often block the current thread when pulling • You wait until a whole operation is finished before you act on the result Malte Bucksch 54 Push-based (Reactive Programming) • You react when new data is “pushed” • You never actively wait for a result • Data is continuously pushed without waiting for the whole to complete
55. Setup Malte Bucksch 55 WLAN: Eppleton 7692 8695 7707 6230 8360
56. Setup https://gitlab.com/quickbirdstudios/rxjava-training 1 2 3 56 WLAN: Eppleton 7692 8695 7707 6230 8360 Malte Bucksch
57. Setup 57 WLAN: Eppleton 7692 8695 7707 6230 8360 1. Run the example-login-app on a phone 2. Run the unit test folder by right-clicking on the test folder Malte Bucksch
58. Everybody ready? Malte Bucksch 58 https://gitlab.com/quickbirdstudios/rxjava-training
59. Just say NO Malte Bucksch 59
60. app\src\test\java\com\quickbirdstudios\ kotlintrainingexercises\basics_exercises Malte Bucksch 60
61. Führe alle Tests aus und stell sicher, dass alle Tests fehlschlagen Run Tests in ‘basics_exercises’ Rechtsklick… Malte Bucksch 61 app\src\test\java\com\quickbirdstudios\ kotlintrainingexercises\basics_exercises
62. RxJava Core Components Malte Bucksch 62
63. The three Os • Observable • Observer • Operator Malte Bucksch 63
64. Rx creates Data-Streams Malte Bucksch 64 Filter (isEmailValid) Map (firstEmailPart) Keyboard Input Observable Operator Observer
65. Observable Malte Bucksch 65 Click events
66. Subscribe to Observable with an Observer Malte Bucksch 66 Observable<Point> mouseClicks = receiveMouseClicks();
67. Subscribe to Observable with an Observer Malte Bucksch 67 Observable<Point> mouseClicks = receiveMouseClicks(); mouseClicks.subscribe(new Observer<Point>() { });
68. Subscribe to Observable with an Observer Malte Bucksch 68 Observable<Point> mouseClicks = receiveMouseClicks(); mouseClicks.subscribe(new Observer<Point>() { @Override public void onNext(Point location) { System.out.println("Click at location: "+location); } });
69. Subscribe to Observable with an Observer Malte Bucksch 69 Observable<Point> mouseClicks = receiveMouseClicks(); mouseClicks.subscribe(new Observer<Point>() { @Override public void onNext(Point location) { System.out.println("Click at location: "+location); } @Override public void onError(Throwable e) { System.out.println("Connection problems!"); } });
70. Subscribe to Observable with an Observer Malte Bucksch 70 Observable<Point> mouseClicks = receiveMouseClicks(); mouseClicks.subscribe(new Observer<Point>() { @Override public void onNext(Point location) { System.out.println("Click at location: "+location); } @Override public void onError(Throwable e) { System.out.println("Connection problems!"); } @Override public void onComplete() { System.out.println("Did you disconnect the mouse?"); } });
71. Subscribe to Observable with an Observer Malte Bucksch 71 Observable<Point> mouseClicks = receiveMouseClicks(); mouseClicks.subscribe(new Observer<Point>() { @Override public void onSubscribe(Disposable d) { System.out.println("New subscriber!"); } @Override public void onNext(Point location) { System.out.println("Click at location: "+location); } @Override public void onError(Throwable e) { System.out.println("Connection problems!"); } @Override public void onComplete() { System.out.println("Did you disconnect the mouse?"); } });
72. onSubscribe, onNext, onError, onComplete Malte Bucksch 72 Click events onSubsribe(Disposable) onNext(Object) onError(Throwable) onComplete()
73. Subscribe to Observable with a single consumer Malte Bucksch 73 Observable<Point> mouseClicks = receiveMouseClicks(); mouseClicks.subscribe(location -> { System.out.println("Click at location: "+location); }); onNext(Location)-Consumer
74. Operators Malte Bucksch 74
75. Categories of Operators • Creating operators (e.g. create, just, range) • Filtering operators (e.g. filter, take) • Reducing operators (e.g. reduce, contains, count) • Transforming operators (e.g. map, flatMap) • Combining operators (e.g. merge, combineLatest) • Time based operators (e.g. buffer, delay) • Threading operators (e.g. subscribeOn, observeOn) • Error handling operators (e.g. onErrorReturn, retry) … Malte Bucksch 75
76. Filter Malte Bucksch 76
77. Filter Example Malte Bucksch 77 Observable<Integer> intObservable = Observable.just(1,2,3,4,5); intObservable.filter(val -> val % 2 == 0) .subscribe(i -> { // Will receive the following values in order: 6, 12 });
78. Map Malte Bucksch 78
79. Map Malte Bucksch 79
80. Map in RxJava Malte Bucksch 80 Observable<Integer> intObservable = Observable.just(1, 2, 3, 4); intObservable.map(val -> val * 10).subscribe(i -> { // Will receive the following values in order: 10, 20, 30, 40 });
81. Imperative vs Declarative Programming How vs What Malte Bucksch 81 In order to do that, let’s first do THIS But don’t forget about THAT True! And in the end let’s finish with THIS I DON’T CARE HOW, JUST DO IT!
82. RxJava Example: Getting users with a blog Malte Bucksch 82 public List<User> getUsersWithABlog(List<User> users) { }
83. RxJava Example: Getting users with a blog Malte Bucksch 83 public List<User> getUsersWithABlog(List<User> users) { List<User> filteredUsers = new ArrayList<>(); for (User user : users) { if (user.hasBlog()) { filteredUsers.add(user); } } return filteredUsers; }
84. RxJava Example: Getting users with a blog Malte Bucksch 84 public Observable<User> getUsersWithABlog(List<User> users) { }
85. RxJava Example: Getting users with a blog Malte Bucksch 85 public Observable<User> getUsersWithABlog(List<User> users) { return Observable.fromIterable(users) .filter(user -> user.hasBlog()) }
86. Rx-Libraries • RxBinding • RxPermissions • RxLifecycle • RxAnimations • RxLocation • RxPaparazzo • … Malte Bucksch 86
87. Example of Rx-Library: RxBinding Malte Bucksch 87 saveButton.setOnClickListener(v -> { ... }); emailEditText.addTextChangedListener(new TextWatcher() { @Override public void beforeTextChanged(CharSequence s, int start, int count, int after) { } @Override public void onTextChanged(CharSequence s, int start, int before, int count) { } @Override public void afterTextChanged(Editable s) { } }); Standard way
88. Example of Rx-Library: RxBinding Malte Bucksch 88 RxTextView.textChanges(emailEditText) .subscribe(newText -> ...); RxView.clicks(saveButton) .subscribe(view -> ...); RxBinding
89. Example of Rx-Library: RxBinding Malte Bucksch 89 RxTextView.textChanges(emailEditText) .filter(this::isValid) .subscribe(newText -> ...); RxView.clicks(saveButton) .subscribe(view -> ...); Ignore invalid Email-Inputs
90. Example of Rx-Library: RxBinding Malte Bucksch 90 RxTextView.textChanges(emailEditText) .map(newText -> newText.toString().trim()) .distinctUntilChanged() .subscribe(newText -> ...); RxView.clicks(saveButton) .subscribe(view -> ...); Ignore irrelevant changes (like adding a space)
91. Example of Rx-Library: RxBinding Malte Bucksch 91 RxTextView.textChanges(emailEditText) // “Haus” -> .map(newText -> newText.toString().trim()) // .distinctUntilChanged() // .subscribe(newText -> ...); // RxView.clicks(saveButton) .subscribe(view -> ...); Ignore irrelevant changes (like adding a space)
92. Example of Rx-Library: RxBinding Malte Bucksch 92 RxTextView.textChanges(emailEditText) // “Haus” -> .map(newText -> newText.toString().trim()) // “Haus” -> .distinctUntilChanged() // .subscribe(newText -> ...); // RxView.clicks(saveButton) .subscribe(view -> ...); Ignore irrelevant changes (like adding a space)
93. Example of Rx-Library: RxBinding Malte Bucksch 93 RxTextView.textChanges(emailEditText) // “Haus” -> .map(newText -> newText.toString().trim()) // “Haus” -> .distinctUntilChanged() // “Haus” -> .subscribe(newText -> ...); // RxView.clicks(saveButton) .subscribe(view -> ...); Ignore irrelevant changes (like adding a space)
94. Example of Rx-Library: RxBinding Malte Bucksch 94 RxTextView.textChanges(emailEditText) // “Haus” -> .map(newText -> newText.toString().trim()) // “Haus” -> .distinctUntilChanged() // “Haus” -> .subscribe(newText -> ...); // “Haus” -> RxView.clicks(saveButton) .subscribe(view -> ...); Ignore irrelevant changes (like adding a space)
95. Example of Rx-Library: RxBinding Malte Bucksch 95 RxTextView.textChanges(emailEditText) // “Haus_” -> .map(newText -> newText.toString().trim()) // .distinctUntilChanged() // .subscribe(newText -> ...); // RxView.clicks(saveButton) .subscribe(view -> ...); Ignore irrelevant changes (like adding a space)
96. Example of Rx-Library: RxBinding Malte Bucksch 96 RxTextView.textChanges(emailEditText) // “Haus_” -> .map(newText -> newText.toString().trim()) // “Haus” -> .distinctUntilChanged() // .subscribe(newText -> ...); // RxView.clicks(saveButton) .subscribe(view -> ...); Ignore irrelevant changes (like adding a space)
97. Example of Rx-Library: RxBinding Malte Bucksch 97 RxTextView.textChanges(emailEditText) // “Haus_” -> .map(newText -> newText.toString().trim()) // “Haus” -> .distinctUntilChanged() // X (filtered) .subscribe(newText -> ...); // RxView.clicks(saveButton) .subscribe(view -> ...); Ignore irrelevant changes (like adding a space)
98. Testing with Rx Malte Bucksch 98
99. Testing async code without RxJava Malte Bucksch 99 void multiplyLargeSet(List<Integer> numbers, int times, Callback callback) // multiplyLargeSet(numbers = [1,2,3], times = 3) -> [3,6,9]
100. Testing async code without RxJava Malte Bucksch 100 @Test public void testMultiplyLargeList() { // given List<Integer> numbers = Arrays.asList(1, 2, 3); // when // then }
101. Testing async code without RxJava Malte Bucksch 101 @Test public void testMultiplyLargeList() { // given List<Integer> numbers = Arrays.asList(1, 2, 3); // when multiplyLargeList(numbers, 2, multipliedNumbers -> { … }); // then }
102. Testing async code without RxJava Malte Bucksch 102 @Test public void testMultiplyLargeList() { // given List<Integer> numbers = Arrays.asList(1, 2, 3); // when multiplyLargeList(numbers, 2, multipliedNumbers -> { … }); // then assertEquals(2, (int) multipliedNumbers.get(0)); assertEquals(4, (int) multipliedNumbers.get(1)); assertEquals(6, (int) multipliedNumbers.get(2)); }
103. Testing async code without RxJava Malte Bucksch 103 @Test public void testMultiplyLargeList() { // given List<Integer> numbers = Arrays.asList(1, 2, 3); // when multiplyLargeList(numbers, 2, multipliedNumbers -> { … }); // then assertEquals(2, (int) multipliedNumbers.get(0)); assertEquals(4, (int) multipliedNumbers.get(1)); assertEquals(6, (int) multipliedNumbers.get(2)); } How to access this async callback’s parameter?
104. Testing async code without RxJava Malte Bucksch 104 @Test public void testMultiplyLargeList() { // given List<Integer> numbers = Arrays.asList(1, 2, 3); // when List<Integer> doubledNumbers = new ArrayList<>(); multiplyLargeList(numbers, 2, multipliedNumbers -> { doubledNumbers.addAll(multipliedNumbers); }); // then assertEquals(2, (int) doubledNumbers.get(0)); assertEquals(4, (int) doubledNumbers.get(1)); assertEquals(6, (int) doubledNumbers.get(2)); }
105. Testing async code without RxJava Malte Bucksch 105 @Test public void testMultiplyLargeList() { // given List<Integer> numbers = Arrays.asList(1, 2, 3); // when CountDownLatch mutex = new CountDownLatch(1); List<Integer> doubledNumbers = new ArrayList<>(); multiplyLargeList(numbers, 2, multipliedNumbers -> { doubledNumbers.addAll(multipliedNumbers); mutex.countDown(); }); mutex.await(); // then assertEquals(2, (int) doubledNumbers.get(0)); assertEquals(4, (int) doubledNumbers.get(1)); assertEquals(6, (int) doubledNumbers.get(2)); }
106. Testing async code without RxJava Malte Bucksch 106 Observable<Integer> multiplyLargeSet(List<Integer> numbers, int times)
107. Testing async code with RxJava Malte Bucksch 107 @Test public void multiplyLargeList() { // given List<Integer> numbers = Arrays.asList(1, 2, 3); // when // then }
108. Testing async code with RxJava Malte Bucksch 108 @Test public void multiplyLargeList() { // given List<Integer> numbers = Arrays.asList(1, 2, 3); // when Observable<Integer> doubledNumbers = multiplyLargeList(numbers, 2); // then }
109. Testing async code with RxJava Malte Bucksch 109 @Test public void multiplyLargeList() { // given List<Integer> numbers = Arrays.asList(1, 2, 3); // when Observable<Integer> doubledNumbers = multiplyLargeList(numbers, 2); // then doubledNumbers.test().assertValues(2, 4, 6); }
110. Loosing the fear of asynchronous code Malte Bucksch 110 “We always thought asynchronous code must be clunky and error-prone. Since we got to know RxJava we live our life in peace.”
111. User experience benefits: Changes propagate automatically Malte Bucksch 111
112. Questions so far? Malte Bucksch 112
113. Hacking Malte Bucksch 113
114. Hacking: RxConsole • TASK: Open “exercises/exercise0_rxconsole/UserInputExercise” and resolve all TODOs HINT: How to execute plain Java-code in Android-Studio (right-click on the file): Malte Bucksch 114
115. Solution Malte Bucksch 115
116. In a perfect Rx-world: No callbacks, No listeners Malte Bucksch 116
117. In a perfect Rx-world: No callbacks, No listeners Malte Bucksch 117 button.setOnClickListener(v -> { //... }); networkClient.searchCafePlaces("Starbucks", cafe -> { //... });
118. In a perfect Rx-world: No callbacks, No listeners Malte Bucksch 118 RxView.clicks(button) .subscribe(view -> { // ... }); rxNetworkClient.searchNearbyCafePlaces("Starbucks") .subscribe(cafes -> { // ... });
119. In a perfect Rx-world: No callbacks, No listeners Malte Bucksch 119 RxView.clicks(button) .filter(…) .subscribe(view -> { // ... }); rxNetworkClient.searchNearbyCafePlaces("Starbucks") .map(…) .subscribe(cafes -> { // ... });
120. The hardest part: Thinking Reactive Malte Bucksch 120
121. Summary • RxJava is library for implementing Functional Reactive Programming (FRP) • ReactiveX is a cross-platform specification • RxJava makes it easier to deal with asynchronous data flows • RxJava make asynchronous code safer by applying principles from functional and declarative programming • In RxJava everything is a stream of values that can be observed • RxJava’s Power is based on its wide range of operators Malte Bucksch 121
122. Questions so far? Malte Bucksch 122
123. Hacking: exercise1_observable_intro Resolve all of the TODOs Malte Bucksch 123
124. Training Agenda • Part 1: RxJava Background and Overview • Part 2: RxJava Basics • Part 3: RxJava Operators • Part 4: Example of a modern UI architecture with RxJava • Part 5: Testing with RxJava • Part 6: RxJava Advanced Malte Bucksch 1
125. Part 2: RxJava Basics Malte Bucksch 2
126. The three Os Malte Bucksch 3 Filter (isEmailValid) Map (firstEmailPart) Keyboard Input Observable Operator Observer
127. The three Os Malte Bucksch 4 Filter (isEmailValid) Map (firstEmailPart) Keyboard Input Observable Operator Observer
128. Creating Observables Malte Bucksch 5
129. Most common ways to create Observables • Observable.just(…) • Observable.from… (e.g. fromIterable, fromArray, fromFuture) • Observable.create(…) • Observable.range(int start, int count) • Observable.empty() / Observable.never() / Observable.error(…) • Observable.generate(…) • Observable.interval(…) • Observable.timer(…) Malte Bucksch 6
130. Most common ways to create Observables • Observable.just(…) • Observable.from… (e.g. fromIterable, fromArray, fromFuture) • Observable.create(…) • Observable.range(int start, int count) • Observable.empty() / Observable.never() / Observable.error(…) • Observable.interval(…) • Observable.timer(…) • Observable.generate(…) Malte Bucksch 7
131. Creating Observables from values: Just Malte Bucksch 8 Observable.just(1, 2, 3).subscribe(val -> { // val will be 1, 2, 3 }); 3 - 2 - 1
132. Creating Observables: from… Malte Bucksch 9 Observable.fromIterable(...) Observable.fromFuture(...) Observable.fromArray(...) Observable.fromCallable(...) Observable.fromPublisher(...)
133. Creating Observables from Arrays Malte Bucksch 10 int[] intArray = {1, 2, 3}; Observable.fromArray(intArray).subscribe(val -> { // val will be 1, 2, 3 });
134. Creating Observables from Iterables Malte Bucksch 11 List<Integer>integerList = new ArrayList<>(); integerList.add(1); integerList.add(2); integerList.add(3); Observable.fromIterable(integerList).subscribe(val -> { // val will be 1, 2, 3 });
135. Creating Observables via an Emitter Malte Bucksch 12 Observable.<Integer>create(emitter -> { }).subscribe(val -> { });
136. Creating Observables via an Emitter Malte Bucksch 13 Observable.<Integer>create(emitter -> { emitter.onNext(1); emitter.onNext(2); emitter.onNext(3); }).subscribe(val -> { // val will be 1, 2, 3 });
137. Creating observables via an Emitter Malte Bucksch 14 Observable.<Integer>create(emitter -> { emitter.onNext(1); emitter.onNext(2); emitter.onNext(3); emitter.onError(new IllegalStateException( "Strange things did happen here...")); }).subscribe(val -> { // val will be 1, 2, 3 }, error -> { // error object after all values were emitted });
138. Creating observables via an Emitter Malte Bucksch 15 Observable.<Integer>create(emitter -> { emitter.onNext(1); emitter.onNext(2); emitter.onNext(3); emitter.onComplete(); }).subscribe(val -> { // val will be 1,2,3 }, throwable -> { // NO errors }, () -> { // onComplete called at the end });
139. You can throw elements, an error or a completion-event into the pipe Malte Bucksch 16 3 - 2 - 1 Observable.<Integer>create(emitter -> { emitter.onNext(1); emitter.onNext(2); emitter.onNext(3); emitter.onError(new IllegalStateException( "Strange things did happen here...")); })
140. Completion of Observables and Errors Malte Bucksch 17 Filter Map Error Completion
141. Operators create new Observables Malte Bucksch 18 Take(2) Map Error Completion Observable Observable
142. Operators create new Observables Malte Bucksch 19 Take(2) Map Completion after 2 elements Observable Observable 3 - 2 - 1 3 - 2 - 1 2 - 1 2x - 1y
143. More ways to create Observables • Observable.just(…) • Observable.from… (e.g. fromIterable, fromArray, fromFuture) • Observable.create(…) • Observable.range(int start, int count) • Observable.empty() / Observable.never() / Observable.error(Throwable exception) • Observable.interval(…) • Observable.generate(…) • Observable.timer(…) Malte Bucksch 20
144. More ways to create Observables Malte Bucksch 21
145. Questions? • Observable.just(…) • Observable.from… (e.g. fromIterable, fromArray, fromFuture) • Observable.create(…) • Observable.range(int start, int count) • Observable.empty() / Observable.never() / Observable.error(…) • Observable.interval(…) • Observable.timer(…) • Observable.generate(…) Malte Bucksch 22
146. The three Os Malte Bucksch 23 Filter (isEmailValid) Map (firstEmailPart) Keyboard Input Observable Operator Observer
147. The three Os Malte Bucksch 24 Filter (isEmailValid) Map (firstEmailPart) Keyboard Input Observable Operator Observer
148. Observers Malte Bucksch 25
149. Subscribe to Observable with an Observer Malte Bucksch 26 Observable<Point> mouseClicks = receiveMouseClicks(); mouseClicks.subscribe(new Observer<Point>() { @Override public void onSubscribe(Disposable d) { System.out.println("New subscriber!"); } @Override public void onNext(Point location) { System.out.println("Click at location: "+location); } @Override public void onError(Throwable e) { System.out.println("Connection problems!"); } @Override public void onComplete() { System.out.println("Did you disconnect the mouse?"); } });
150. Subscribe to Observable with a single consumer Malte Bucksch 27 Observable<Point> mouseClicks = receiveMouseClicks(); mouseClicks.subscribe(location -> { System.out.println("Click at location: “ + location); });
151. Subscribe to Observable with a multiple consumers Malte Bucksch 28 Observable<Point> mouseClicks = receiveMouseClicks(); mouseClicks.subscribe(location -> { System.out.println("Click at location: " + location); }, throwable -> { // onError );
152. Subscribe to Observable with a multiple consumers Malte Bucksch 29 Observable<Point> mouseClicks = receiveMouseClicks(); mouseClicks.subscribe(location -> { System.out.println("Click at location: " + location); }, throwable -> { // onError }, () -> { // onComplete });
153. Subscribe to Observable with a multiple consumers Malte Bucksch 30 Observable<Point> mouseClicks = receiveMouseClicks(); mouseClicks.subscribe(location -> { System.out.println("Click at location: " + location); }, throwable -> { // onError }, () -> { // onComplete }, disposable -> { // onSubscribe });
154. Quiz Malte Bucksch 31
155. Which methods are called in which order? Case 1: Two coffee places where found Malte Bucksch 32 NetworkClient networkClient = new NetworkClient(); networkClient.findNearbyCoffeePlaces("Starbucks") .subscribe(new Observer<Cafe>() { @Override public void onSubscribe(Disposable d) { ... } @Override public void onNext(Cafe cafe) { ... } @Override public void onError(Throwable e) { ... } @Override public void onComplete() { ... } }); #1 #2 (2x) #3
156. Which methods are called in which order? Case 2: No coffee place is found Malte Bucksch 33 NetworkClient networkClient = new NetworkClient(); networkClient.findNearbyCoffeePlaces("Starbucks") .subscribe(new Observer<Cafe>() { @Override public void onSubscribe(Disposable d) { ... } @Override public void onNext(Cafe cafe) { ... } @Override public void onError(Throwable e) { ... } @Override public void onComplete() { ... } }); #1 #2
157. Which methods are called in which order? Case 3: There is no internet connection Malte Bucksch 34 NetworkClient networkClient = new NetworkClient(); networkClient.findNearbyCoffeePlaces("Starbucks") .subscribe(new Observer<Cafe>() { @Override public void onSubscribe(Disposable d) { ... } @Override public void onNext(Cafe cafe) { ... } @Override public void onError(Throwable e) { ... } @Override public void onComplete() { ... } }); #1 #2
158. Subscription callbacks onSubscribe: for every new subscriber onNext: for every new value onError: once after an error XOR onComplete: once after completion Malte Bucksch 35
159. Which notifications do you get? Case 1: Two coffee places where found Malte Bucksch 36 networkClient.findNearbyCoffeePlaces("Starbucks") .subscribe(cafe -> { ... }); onNext, onComplete, onError, onSubscribe ?
160. Solution Case 1: Two coffee places where found Malte Bucksch 37 networkClient.findNearbyCoffeePlaces("Starbucks") .subscribe(cafe -> { ... }); onNext (2x), onComplete, onError, onSubscribe c
161. Which notifications do you get? Case 2: No coffee places where found Malte Bucksch 38 networkClient.findNearbyCoffeePlaces("Starbucks") .subscribe(cafe -> { ... }); onNext, onComplete, onError, onSubscribe ?
162. Solution Case 2: No coffee places where found Malte Bucksch 39 networkClient.findNearbyCoffeePlaces("Starbucks") .subscribe(cafe -> { ... }); onNext, onComplete, onError, onSubscribe NOTHING
163. Which notifications do you get? Case 2: No coffee places where found Malte Bucksch 40 networkClient.findNearbyCoffeePlaces("Starbucks") .subscribe(cafe -> { ... }, throwable -> { ... }, () -> { ... }); onNext, onComplete, onError, onSubscribe ?
164. Solution Case 2: No coffee places where found Malte Bucksch 41 networkClient.findNearbyCoffeePlaces("Starbucks") .subscribe(cafe -> { ... }, throwable -> { ... }, () -> { ... }); onNext, onComplete (1x), onError, onSubscribe
165. Which notifications do you get? Case 3: No internet connection Malte Bucksch 42 networkClient.findNearbyCoffeePlaces("Starbucks") .subscribe(cafe -> { ... }); onNext, onComplete, onError, onSubscribe ?
166. Solution Case 3: No internet connection Malte Bucksch 43 networkClient.findNearbyCoffeePlaces("Starbucks") .subscribe(cafe -> { ... }); CRASH!
167. Solution Case 3: No internet connection Malte Bucksch 44 networkClient.findNearbyCoffeePlaces("Starbucks") .subscribe(cafe -> { ... }, throwable -> { ... });
168. Disposing subscriptions Malte Bucksch 45
169. Disposing subscriptions Malte Bucksch 46 Observable<Point> mouseClicks = receiveMouseClicks(); mouseClicks.subscribe(location -> { System.out.println("Click at location: " + location); });
170. Disposing subscriptions Malte Bucksch 47 private Disposable disposable; … Observable<Point> mouseClicks = receiveMouseClicks(); disposable = mouseClicks.subscribe(location -> { System.out.println("Click at location: " + location); });
171. Disposing subscriptions Malte Bucksch 48 private Disposable disposable; … Observable<Point> mouseClicks = receiveMouseClicks(); disposable = mouseClicks.subscribe(location -> { System.out.println("Click at location: " + location); }); … @Override protected void onDestroy() { disposable.dispose(); super.onDestroy(); }
172. Questions so far? Malte Bucksch 49
173. Hacking: exercise2_creation_subscription Malte Bucksch 50
174. Hot vs. Cold Observables Malte Bucksch 51
175. Cold Observables Malte Bucksch 52 Observable<String> observable = Observable.just("A", "B", "C", "D", "E"); // observer 1 observable.subscribe(val -> { }); // observer 2 observable.subscribe(val -> { });
176. Cold Observables Malte Bucksch 53 Observable<String> observable = Observable.just("A", "B", "C", "D", "E"); // observer 1 observable.subscribe(val -> { // "A", "B", "C", "D", "E" will be received in order }); // observer 2 observable.subscribe(val -> { });
177. Cold Observables Malte Bucksch 54 Observable<String> observable = Observable.just("A", "B", "C", "D", "E"); // observer 1 observable.subscribe(val -> { // "A", "B", "C", "D", "E" will be received in order }); // observer 2 observable.subscribe(val -> { // What do I receive? });
178. Cold Observables Malte Bucksch 55 Observable<String> observable = Observable.just("A", "B", "C", "D", "E"); // observer 1 observable.subscribe(val -> { // "A", "B", "C", "D", "E" will be received in order }); // observer 2 observable.subscribe(val -> { // Again, "A", "B", "C", "D", "E" will be received in order });
179. Cold Observable Malte Bucksch 56
180. Cold Observables Malte Bucksch 57 Observable<String> observable = Observable.just("A", "B", "C", "D", "E"); *Grillen Zirpen*
181. Cold Observables Malte Bucksch 58 Observable<String> observable = Observable.just("A", "B", "C", "D", "E"); // observer 1 observable.subscribe(val -> { // "A", "B", "C", "D", "E" will be received in order });
182. Cold Observables Malte Bucksch 59 Observable<String> observable = Observable.just("A", "B", "C", "D", "E"); // observer 1 observable.subscribe(val -> { // "A", "B", "C", "D", "E" will be received in order }); // observer 2 observable.subscribe(val -> { // Again, "A", "B", "C", "D", "E" will be received in order });
183. Malte Bucksch 60 Cold Observable: Example
184. Hot Observables Malte Bucksch 61
185. Hot Observable: Example Malte Bucksch 62
186. Basic difference: Cold vs Hot Malte Bucksch 63
187. Cold creates & listens to Producer, Hot only listens to Producer Malte Bucksch 64 // COLD Observable<Object> cold = Observable.create(emitter -> { });
188. Cold creates & listens to Producer, Hot only listens to Producer Malte Bucksch 65 // COLD Observable<Object> cold = Observable.create(emitter -> { Producer producer = new Producer(); producer.addListener(newProducerValue -> { emitter.onNext(newProducerValue); }); });
189. Cold creates & listens to Producer, Hot only listens to Producer Malte Bucksch 66 // COLD Observable<Object> cold = Observable.create(emitter -> { Producer producer = new Producer(); producer.addListener(newProducerValue -> { emitter.onNext(newProducerValue); }); }); // HOT Observable<Object> hot = Observable.create(emitter -> { });
190. Cold creates & listens to Producer, Hot only listens to Producer Malte Bucksch 67 // COLD Observable<Object> cold = Observable.create(emitter -> { Producer producer = new Producer(); producer.addListener(newProducerValue -> { emitter.onNext(newProducerValue); }); }); // HOT Producer producer = new Producer(); Observable<Object> hot = Observable.create(emitter -> { producer.addListener(newProducerValue -> { emitter.onNext(newProducerValue); }); });
191. Is it a Hot or Cold Observable? Malte Bucksch 68
192. Price alerts from Stock Exchange Malte Bucksch 69
193. Database Query Malte Bucksch 70
194. Keyboard Events Malte Bucksch 71
195. Broadcasts/Messages inside your system Malte Bucksch 72
196. Observable einer Liste von Zahlen Malte Bucksch 73
197. Keyboard Input Malte Bucksch 74 Producer producer = new Producer(); Observable<Object> observable = Observable.create(emitter -> { producer.addListener(newProducerValue -> { emitter.onNext(newProducerValue); }); });
198. Malte Bucksch 75 Observable<Object> observable = Observable.create(emitter -> { Producer producer = new Producer(); producer.addListener(newProducerValue -> { emitter.onNext(newProducerValue); }); });
199. Summary: Hot vs Cold Observables Cold • Nothing happens if there is no Observer • Producer created for each Observer • Values are produced twice if two Observers subscribe Malte Bucksch 76 Hot • Data flows already, even if there is no Observer • Producer created once only but independent of Observers • Values are produced only once, even if two Observers subscribe
200. Summary: Observables • You can create Observables via many different operators like: • Observable.create, Observable.just, Observable.from… • You can subscribe to an Observable • Via an Observer • Via one or more Consumers (short-form) Malte Bucksch 77
201. Questions so far? Malte Bucksch 78
202. Other observable types • Single • Maybe • Completable • Subjects • Flowable Malte Bucksch 79
203. Other observable types • Single • Maybe • Completable • Subjects • Flowable Malte Bucksch 80
204. Single Malte Bucksch 81 Observable Single Emits EXACTLY one element
205. Single Malte Bucksch 82 Observable Single Similar to a Future or Promise
206. Maybe Malte Bucksch 83 Single Maybe ? Emits EXACTLY one OR NO element
207. Completable Malte Bucksch 84 Single Completable Emits NO items, just an onComplete
208. Live coding Malte Bucksch 85
209. Lifecycle Observable: onSubscribe -> onNext(value) -> onNext(value) -> … -> [onError XOR onComplete] Single: onSubscribe -> [onError XOR onSuccess(value)] Maybe: onSubscribe -> [onError XOR onSuccess(value) XOR onComplete] Completable: onSubscribe -> [onError XOR onComplete] Malte Bucksch 86
210. Flowable Malte Bucksch 87 Observable Observable with too much output to process
211. Flowable Malte Bucksch 88 Observable Flowable Requests more elements
212. Subjects Malte Bucksch 89 Observable Observer
213. Subjects Malte Bucksch 90 Observer + Observable Subject
214. RxJava 2: No NULL values allowed Observable.just(null); Malte Bucksch 91
215. RxJava 2: No NULL values allowed Observable.just(Optional.empty()); Malte Bucksch 92
216. Questions so far? Malte Bucksch 93
217. Training Agenda • Part 1: RxJava Background and Overview • Part 2: RxJava Basics • Part 3: RxJava Operators • Part 4: Example of a modern UI architecture with RxJava • Part 5: Testing with RxJava • Part 6: RxJava Advanced Malte Bucksch 1
218. Part 3: RxJava Operators Malte Bucksch 2
219. The three Os Malte Bucksch 3 Filter (isEmailValid) Map (firstEmailPart) Keyboard Input Observable Operator Observer
220. The three Os Malte Bucksch 4 Filter (isEmailValid) Map (firstEmailPart) Keyboard Input Observable Operator Observer
221. Categories of Operators • Filtering operators (e.g. filter, take) • Transforming operators (e.g. map, flatMap) • Aggregation operators (e.g. reduce, contains, count) • Combining operators (e.g. merge, combineLatest) • Time based operators (e.g. buffer, delay) • Error handling operators (e.g. onErrorReturn, retry) • Threading operators (e.g. subscribeOn, observeOn) … Malte Bucksch 5
222. Operators Malte Bucksch 6 Observable<Integer> intObservable = Observable.create(emitter -> { emitter.onNext(1); emitter.onNext(2); emitter.onNext(3); emitter.onNext(4); emitter.onNext(5); emitter.onComplete(); }); intObservable .subscribe(i -> { // Will receive the following values in order: 1, 2, 3, 4, 5 });
223. Operators Malte Bucksch 7 Observable<Integer> intObservable = Observable.create(emitter -> { emitter.onNext(1); emitter.onNext(2); emitter.onNext(3); emitter.onNext(4); emitter.onNext(5); emitter.onComplete(); }); intObservable.map(val -> val * 3) .subscribe(i -> { // Will receive the following values in order: 3, 6, 9, 12, 15 });
224. Operators Malte Bucksch 8 Observable<Integer> intObservable = Observable.create(emitter -> { emitter.onNext(1); emitter.onNext(2); emitter.onNext(3); emitter.onNext(4); emitter.onNext(5); emitter.onComplete(); }); intObservable.map(val -> val * 3) .filter(val -> val % 2 == 0) .subscribe(i -> { // Will receive the following values in order: 6, 12 });
225. Best practice: Use the operators Malte Bucksch 9 Observable<Integer> intObservable = Observable.create(emitter -> { emitter.onNext(1); emitter.onNext(2); emitter.onNext(3); emitter.onNext(4); emitter.onNext(5); emitter.onComplete(); }); intObservable.subscribe(i -> { int multipliedVal = i * 3; if (multipliedVal % 2 == 0) { // Will receive the following values in order: 6, 12 } });
226. Best practice: Use the operators Malte Bucksch 10 Observable<Integer> intObservable = Observable.create(emitter -> { emitter.onNext(1); emitter.onNext(2); emitter.onNext(3); emitter.onNext(4); emitter.onNext(5); emitter.onComplete(); }); intObservable.subscribe(i -> { int multipliedVal = i * 3; if (multipliedVal % 2 == 0) { // Will receive the following values in order: 6, 12 } });
227. Operators Malte Bucksch 11 Observable<Integer> intObservable = Observable.create(emitter -> { emitter.onNext(1); emitter.onNext(2); emitter.onNext(3); emitter.onNext(4); emitter.onNext(5); emitter.onComplete(); }); intObservable.map(val -> val * 3) .filter(val -> val % 2 == 0) .subscribe(i -> { // Will receive the following values in order: 6, 12 });
228. Marble Diagrams Malte Bucksch 12
229. Marble Diagrams: Successful completion Malte Bucksch 13
230. Marble Diagrams: Error Malte Bucksch 14
231. Marbe Diagrams: Filter Malte Bucksch 15 Color Shape
232. Marble Example Diagram: Filter Malte Bucksch 16
233. Marble Riddle: What do I produce? 17
234. Marbe Riddle: What do I produce? Malte Bucksch 18 ?
235. Marble Riddle: Who am I? 19
236. Marble Riddle: Who am I? Malte Bucksch 20 Name?
237. Operators in Action Malte Bucksch 21
238. Categories of Operators • Filtering operators (e.g. filter, take) • Transforming operators (e.g. map, flatMap) • Aggregation operators (e.g. reduce, contains, count) • Combining operators (e.g. merge, combineLatest) • Time based operators (e.g. buffer, delay) • Error handling operators (e.g. onErrorReturn, retry) • Threading operators (e.g. subscribeOn, observeOn) … Malte Bucksch 22
239. Filtering Operators • filter • take/takeLast • skip/skipLast • distinct • sample … Malte Bucksch 23
240. Take Malte Bucksch 24
241. Take Malte Bucksch 25
242. Take Malte Bucksch 26
243. Skip Malte Bucksch 27
244. Skip Malte Bucksch 28
245. Skip Malte Bucksch 29
246. Distinct Malte Bucksch 30
247. Distinct Malte Bucksch 31
248. Sample Malte Bucksch 32
249. Sample Malte Bucksch 33
250. Live coding: Filtering operators Malte Bucksch 34
251. Lazy evaluation of RxJava Malte Bucksch 35
252. Lazy evaluation of RxJava Malte Bucksch 36 public static void main(String[]args){ System.out.println("Starting the system..."); }
253. Lazy evaluation of RxJava Malte Bucksch 37 public static void main(String[]args){ System.out.println("Starting the system..."); Observable.<Integer>create(emitter -> { System.out.println("Starting the computation right now"); }); }
254. Lazy evaluation of RxJava Malte Bucksch 38 public static void main(String[]args){ System.out.println("Starting the system..."); Observable.<Integer>create(emitter -> { System.out.println("Starting the computation right now"); int result = *crazy, expensive, complicated computation*; emitter.onNext(result); emitter.onComplete(); }); }
255. Lazy evaluation of RxJava Malte Bucksch 39 public static void main(String[]args){ System.out.println("Starting the system..."); Observable.<Integer>create(emitter -> { System.out.println("Starting the computation right now"); int result = *crazy, expensive, complicated computation*; emitter.onNext(result); emitter.onComplete(); }); } What will be printed? Output: "Starting the system..."
256. Lazy evaluation of RxJava Malte Bucksch 40 public static void main(String[]args) { System.out.println("Starting the system..."); Observable.<Integer>create(emitter -> { System.out.println("Starting computation…"); int result = *crazy, expensive, complicated computation *; emitter.onNext(result); emitter.onComplete(); }).subscribe(integer -> { System.out.println("Received: " + integer); }); } What will be printed? Output: "Starting the system...“ "Starting computation…“ "Received: 2332”
257. Lazy evaluation of RxJava Malte Bucksch 41 Observable.just(1,2,3,4,5)
258. Lazy evaluation of RxJava Malte Bucksch 42 Observable.just(1,2,3,4,5) .map(value -> { System.out.println("computing..."); int result = *expensive computation*; return result; })
259. Lazy evaluation of RxJava Malte Bucksch 43 Observable.just(1,2,3,4,5) .map(value -> { System.out.println("computing..."); int result = *expensive computation*; return result; }) .take(2)
260. Lazy evaluation of RxJava Malte Bucksch 44 Observable.just(1,2,3,4,5) .map(value -> { System.out.println("computing..."); int result = *expensive computation*; return result; }) .take(2) .subscribe(result -> { System.out.println("Received result: "+result); });
261. Lazy evaluation of RxJava Malte Bucksch 45 Observable.just(1,2,3,4,5) .map(value -> { System.out.println("computing..."); int result = *expensive computation*; return result; }) .take(2) .subscribe(result -> { System.out.println("Received result: "+result); }); What will be printed? Output: computing... Received result: 1 computing... Received result: 2
262. Questions? • filter: Filter out elements that do not meet a certain criteria • skip/skipLast: Skip elements from start of stream or end • take/takeLast: Take only elements from start of stream or end • distinct: Filter out elements that have been emitted before • sample: Filter out all elements except for a small subset Malte Bucksch 46
263. Categories of Operators • Filtering operators (e.g. filter, take) • Transforming operators (e.g. map, flatMap) • Aggregation operators (e.g. reduce, contains, count) • Combining operators (e.g. merge, combineLatest) • Time based operators (e.g. buffer, delay) • Error handling operators (e.g. onErrorReturn, retry) • Threading operators (e.g. subscribeOn, observeOn) … Malte Bucksch 47
264. Transforming Operators • Map • FlatMap • Scan • … Malte Bucksch 48
265. Map Malte Bucksch 49
266. Map Malte Bucksch 50
267. flatMap(value -> Observable) Malte Bucksch 51 .flatMap
268. flatMap(value -> Observable) Malte Bucksch 52 flatMap Observable Observable
269. Using flatMap to communicate with Search API Malte Bucksch 53 Please enter your search query… Café Search
270. Using flatMap to communicate with Search API Malte Bucksch 54 NetworkSearchClient searchClient = new NetworkSearchClient(); final Observable<String> textChanges = RxTextView.textChanges(searchField);
271. Using flatMap to communicate with Search API Malte Bucksch 55 NetworkSearchClient searchClient = new NetworkSearchClient(); final Observable<String> textChanges = RxTextView.textChanges(searchField); final Observable<Cafe> cozyCafes = textChanges .map(newText -> newText.trim()) …
272. Using flatMap to communicate with Search API Malte Bucksch 56 NetworkSearchClient searchClient = new NetworkSearchClient(); final Observable<String> textChanges = RxTextView.textChanges(searchField); final Observable<Cafe> cozyCafes = textChanges .map(newText -> newText.trim()) .flatMap(newText -> searchClient.searchCafes(newText)) Signature: Observable<Cafe> searchCafes(String searchQuery) { ... }
273. Using flatMap to communicate with Search API Malte Bucksch 57 NetworkSearchClient searchClient = new NetworkSearchClient(); final Observable<String> textChanges = RxTextView.textChanges(searchField); final Observable<Cafe> cozyCafes = textChanges .map(newText -> newText.trim()) .flatMap(newText -> searchClient.searchCafes(newText)) .filter(cafe -> cafe.isCozyAndWarm());
274. Using flatMap to communicate with Search API Malte Bucksch 58 NetworkSearchClient searchClient = new NetworkSearchClient(); final Observable<String> textChanges = RxTextView.textChanges(searchField); final Observable<Cafe> cozyCafes = textChanges .map(newText -> newText.trim()) .flatMap(newText -> searchClient.findCoffeePlaces(newText)) .filter(cafe -> cafe.isCozyAndWarm()); cozyCafes.subscribe(cafe -> System.out.print(cafe.name));
275. flatMap(value -> Observable) Malte Bucksch 59
276. Live coding: Transforming operators Malte Bucksch 60 Useful shortcuts: Ctrl+Q = Docs Alt+Enter = Resolve issue
277. Questions? • map: transform elements • flatMap: receive elements from a second Observable in the current Observable Malte Bucksch 61
278. Categories of Operators • Filtering operators (e.g. filter, take) • Transforming operators (e.g. map, flatMap) • Aggregation operators (e.g. reduce, contains, count) • Combining operators (e.g. merge, combineLatest) • Time based operators (e.g. buffer, delay) • Error handling operators (e.g. onErrorReturn, retry) • Threading operators (e.g. subscribeOn, observeOn) … Malte Bucksch 62
279. Aggregation Operators Operators that operate on the entire sequence of emitted items • contains() • all() • reduce() Malte Bucksch 63
280. contains() Malte Bucksch 64
281. contains() Malte Bucksch 65
282. contains() Malte Bucksch 66
283. all(predicate) Malte Bucksch 67
284. all(predicate) Malte Bucksch 68
285. all(predicate) Malte Bucksch 69 all
286. reduce(reduceFunction) Malte Bucksch 70
287. reduce(reduceFunction) Malte Bucksch 71
288. reduce(reduceFunction) Malte Bucksch 72
289. reduce(reduceFunction) Malte Bucksch 73 Current time 3
290. reduce(reduceFunction) Malte Bucksch 74 Current time 36
291. reduce(reduceFunction) Malte Bucksch 75 Current time 610
292. reduce(reduceFunction) Malte Bucksch 76 Current time 1015
293. reduce(reduceFunction) Malte Bucksch 77 Current time 15
294. Live coding: Aggregation operators Malte Bucksch 78
295. Questions? • contains: check if the Observable emitted a certain element • all: check if ALL elements match a criteria • reduce: combine all elements one after another to single result value Malte Bucksch 79
296. Hacking: exercise3_operators_part1 Malte Bucksch 80
297. Categories of Operators • Filtering operators (e.g. filter, take) • Transforming operators (e.g. map, flatMap) • Aggregation operators (e.g. reduce, contains, count) • Combining operators (e.g. merge, combineLatest) • Time based operators (e.g. buffer, delay) • Error handling operators (e.g. onErrorReturn, retry) • Threading operators (e.g. subscribeOn, observeOn) • … Malte Bucksch 81
298. Combining Operators • merge • combineLatest • Zip … Malte Bucksch 82
299. Merge Malte Bucksch 83
300. Merge Malte Bucksch 84
301. Merge Malte Bucksch 85
302. combineLatest Malte Bucksch 86
303. combineLatest Malte Bucksch 87
304. combineLatest Malte Bucksch 88 Current time
305. combineLatest Malte Bucksch 89 Current time
306. combineLatest Malte Bucksch 90 Current time
307. combineLatest Malte Bucksch 91 Current time
308. combineLatest Malte Bucksch 92 Current time
309. combineLatest Malte Bucksch 93 Current time
310. combineLatest Malte Bucksch 94
311. Zip Malte Bucksch 95
312. Zip Malte Bucksch 96 Observable2 Observable1 Result-Observable
313. Zip Malte Bucksch 97
314. Live coding: Combining operators Malte Bucksch 98
315. Questions? • merge: merge the emissions of multiple Observables into one • combineLatest: combine the latest emissions of multiple Observables into a combined value • zip: combine elements of multiple Observables respecting their order Malte Bucksch 99
316. Categories of Operators • Filtering operators (e.g. filter, take) • Transforming operators (e.g. map, flatMap) • Aggregation operators (e.g. reduce, contains, count) • Combining operators (e.g. merge, combineLatest) • Time based operators (e.g. buffer, delay) • Error handling operators (e.g. onErrorReturn, retry) • Threading operators (e.g. subscribeOn, observeOn) • … Malte Bucksch 100
317. Time-based operators • delay • timeout • buffer … Malte Bucksch 101
318. delay(time) Malte Bucksch 102
319. delay(time) Malte Bucksch 103
320. delay(time) Malte Bucksch 104
321. Buffer(count/time) Malte Bucksch 105
322. Buffer(count) Malte Bucksch 106
323. Buffer(time) Malte Bucksch 107
324. Live coding: Time-based Operators Malte Bucksch 108
325. Questions? • delay: delay the emissions of an Observable by a certain time • timeout: throw error if the Observable didn’t complete in a specific time range • buffer: buffer the elements in a certain time span into a list of elements Malte Bucksch 109
326. Categories of Operators • Filtering operators (e.g. filter, take) • Transforming operators (e.g. map, flatMap) • Aggregation operators (e.g. reduce, contains, count) • Combining operators (e.g. merge, combineLatest) • Time based operators (e.g. buffer, delay) • Error handling operators (e.g. onErrorReturn, retry) • Threading operators (e.g. subscribeOn, observeOn) … Malte Bucksch 110
327. Error-handling Operators • onError… • onErrorReturnItem • onErrorResumeNext • … • Retry Malte Bucksch 111
328. onErrorReturnItem(item) Malte Bucksch 112
329. onErrorResumeNext(observable) Malte Bucksch 113
330. onErrorResumeNext(observable) Malte Bucksch 114
331. retry() Malte Bucksch 115
332. retry() Malte Bucksch 116
333. Live coding: NewsService Malte Bucksch 117
334. Questions so far? Malte Bucksch 118
335. Questions? • onError… • onErrorReturnItem: return a single item instead of emitting an error • onErrorResumeNext: subscribe to another Observable instead of emitting an error • Retry: subscribe to the same Observable again if an error was emitted Malte Bucksch 119
336. Hacking: exercise4_operators_part2 Malte Bucksch 120
337. Categories of Operators • Filtering operators (e.g. filter, take) • Transforming operators (e.g. map, flatMap) • Aggregation operators (e.g. reduce, contains, count) • Combining operators (e.g. merge, combineLatest) • Time based operators (e.g. buffer, delay) • Error handling operators (e.g. onErrorReturn, retry) • Threading operators (e.g. subscribeOn, observeOn) … Malte Bucksch 121
338. Threading Operators • SubscribeOn • ObserveOn Malte Bucksch 122
339. Fetching search results: WITHOUT Rx button.setOnClickListener(view -> { new Thread(() -> networkClient.fetchSearchResults(query, (results, error) -> { runOnUiThread(() -> { if (error != null) showError(error); else showResults(results); }); }) ).start(); }); Malte Bucksch 123
340. Fetching search results: WITH Rx RxView.clicks(button) .flatMap(view -> networkClient.fetchSearchResults(query)) .subscribeOn(Schedulers.newThread()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(this::showResults, this::showError); Malte Bucksch 124
341. subscribeOn(scheduler) Malte Bucksch 125
342. subscribeOn(scheduler) Malte Bucksch 126
343. observeOn(scheduler) vs subscribeOn(scheduler) 127 Can reasonably be called multiple times Gets called only once Malte Bucksch
344. Quiz Malte Bucksch 128
345. What will be printed? Malte Bucksch 129 print("Before"); Observable.<String>create(emitter -> { print("Creating Observable"); emitter.onNext("test"); emitter.onComplete(); }).subscribe(new Observer<String>() { public void onSubscribe(Disposable d) { print("onSubscribe()"); } public void onNext(String value) { print("onNext(): " + value); } public void onComplete() { print("onComplete()"); } public void onError(Throwable e) { } }); print("After"); Before onSubscribe() After Creating Observable onNext(): test onComplete() A Before onSubscribe() Creating Observable onNext(): test onComplete() After B Before onSubscribe() Creating Observable After onNext(): test onComplete() C
346. What will be printed? Malte Bucksch 130 print("Before"); Observable.<String>create(emitter -> { print("Creating Observable"); emitter.onNext("test"); emitter.onComplete(); }).subscribe(new Observer<String>() { public void onSubscribe(Disposable d) { print("onSubscribe()"); } public void onNext(String value) { print("onNext(): " + value); } public void onComplete() { print("onComplete()"); } public void onError(Throwable e) { } }); print("After"); Before onSubscribe() After Creating Observable onNext(): test onComplete() A Before onSubscribe() Creating Observable onNext(): test onComplete() After B Before onSubscribe() Creating Observable After onNext(): test onComplete() C
347. Quiz Malte Bucksch 131
348. What will be printed? Malte Bucksch 132 print("Before"); Observable.<String>create(emitter -> { print("Creating Observable"); emitter.onNext("test"); emitter.onComplete(); }) .subscribeOn(Schedulers.newThread()) .subscribe(new Observer<String>() { public void onSubscribe(Disposable d) { print("onSubscribe()"); } public void onNext(String value) { print("onNext(): " + value); } public void onComplete() { print("onComplete()"); } public void onError(Throwable e) { } }); print("After"); Before onSubscribe() After Creating Observable onNext(): test onComplete() A Before onSubscribe() Creating Observable onNext(): test onComplete() After B Before onSubscribe() Creating Observable After onNext(): test onComplete() C
349. What will be printed? Malte Bucksch 133 print("Before"); Observable.<String>create(emitter -> { print("Creating Observable"); emitter.onNext("test"); emitter.onComplete(); }) .subscribeOn(Schedulers.newThread()) .subscribe(new Observer<String>() { public void onSubscribe(Disposable d) { print("onSubscribe()"); } public void onNext(String value) { print("onNext(): " + value); } public void onComplete() { print("onComplete()"); } public void onError(Throwable e) { } }); print("After"); Before onSubscribe() After Creating Observable onNext(): test onComplete() A Before onSubscribe() Creating Observable onNext(): test onComplete() After B Before onSubscribe() Creating Observable After onNext(): test onComplete() C
350. Quiz Malte Bucksch 134
351. What will be printed? Malte Bucksch 135 print("Before"); Observable.<String>create(emitter -> { print("Creating Observable"); emitter.onNext("test"); emitter.onComplete(); }) .observeOn(Schedulers.newThread()) .subscribe(new Observer<String>() { public void onSubscribe(Disposable d) { print("onSubscribe()"); } public void onNext(String value) { print("onNext(): " + value); } public void onComplete() { print("onComplete()"); } public void onError(Throwable e) { } }); print("After"); Before onSubscribe() After Creating Observable onNext(): test onComplete() A Before onSubscribe() Creating Observable onNext(): test onComplete() After B Before onSubscribe() Creating Observable After onNext(): test onComplete() C
352. What will be printed? Malte Bucksch 136 print("Before"); Observable.<String>create(emitter -> { print("Creating Observable"); emitter.onNext("test"); emitter.onComplete(); }) .observeOn(Schedulers.newThread()) .subscribe(new Observer<String>() { public void onSubscribe(Disposable d) { print("onSubscribe()"); } public void onNext(String value) { print("onNext(): " + value); } public void onComplete() { print("onComplete()"); } public void onError(Throwable e) { } }); print("After"); Before onSubscribe() After Creating Observable onNext(): test onComplete() A Before onSubscribe() Creating Observable onNext(): test onComplete() After B Before onSubscribe() Creating Observable After onNext(): test onComplete() C
353. Summary Malte Bucksch 137 print("Before"); Observable.<String>create(emitter -> { print("Creating Observable"); emitter.onNext("test"); emitter.onComplete(); }) … ? .subscribe(new Observer<String>() { public void onSubscribe(Disposable d) { print("onSubscribe()"); } public void onNext(String value) { print("onNext(): " + value); } public void onComplete() { print("onComplete()"); } public void onError(Throwable e) { } }); print("After"); Before onSubscribe() After Creating Observable onNext(): test onComplete() A Before onSubscribe() Creating Observable onNext(): test onComplete() After B Before onSubscribe() Creating Observable After onNext(): test onComplete() C Standard case (no operator) .subscribeOn(Schedulers.newThread()) .obseveOn(Schedulers.newThread())
354. Schduling tasks: Without RxJava button.setOnClickListener(view -> { new Thread(() -> networkClient.fetchSearchResults(query, (results, error) -> { runOnUiThread(() -> { if (error != null) showError(error); else showResults(results); }); }) ).start(); }); Malte Bucksch 138
355. Scheduling tasks with RxJava: Abstracting the details away RxView.clicks(button) .flatMap(view -> networkClient.fetchSearchResults(query)) .subscribeOn(Schedulers.newThread()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(this::showResults, this::showError); Malte Bucksch 139
356. Different types of Schedulers computeSomething() .subscribeOn(Schedulers.computation()) .subscribe(result -> { }); computeSomething() .subscribeOn(Schedulers.io()) .subscribe(result -> { }); computeSomething() .subscribeOn(Schedulers.newThread()) .subscribe(result -> { }); computeSomething() .subscribeOn(Schedulers.single()) .subscribe(result -> { }); Malte Bucksch 140
357. Questions? • subscribeOn: execute the subscription of an Observable on a different thread • observeOn: execute the Observer code of an Observable on a different thread • Different types of Schedulers: newThread, io, computation, single … Malte Bucksch 141
358. Interacting with a world outside of Rx Malte Bucksch 142
359. Interacting with a world outside of Rx • Using Rx in Non-rx code: Blocking operators • Blocking first, last … • Collection operators • toList() • toSortedList() • toMap() and toMultiMap() • collect() • Using Non-Rx Code with Rx • Adapting interfaces of Non-Rx code to Rx Malte Bucksch 143
360. Live coding: BlockingGet in tests and Rx- Interfaces Malte Bucksch 144
361. Questions? • Using Rx in Non-rx code: Blocking operators • Blocking first: fetch first element of Observable by blocking the thread until Observable emitted an element • Collection operators: convert Observable element emissions to a List by blocking the thread until Observable completed e.g. toList() • Using Non-Rx Code with Rx • Adapting interfaces of Non-Rx code to Rx Malte Bucksch 145
362. Questions so far? Malte Bucksch 146
363. Hacking: exercise5_operators_part3 Malte Bucksch 147
364. Subjects Malte Bucksch 1
365. Subjects Malte Bucksch 2 Observable Observer
366. Subjects Malte Bucksch 3 Observer + Observable Subject
367. Different types of Subjects • PublishSubject • BehaviourSubject • ReplaySubject • AsyncSubject Malte Bucksch 4
368. Different types of Subjects • PublishSubject • BehaviourSubject • ReplaySubject • AsyncSubject Malte Bucksch 5
369. PublishSubject Malte Bucksch 6
370. PublishSubject Malte Bucksch 7 Observer + Observable Subject
371. PublishSubject Malte Bucksch 8
372. Subject are Observers and Observables at the same time Malte Bucksch 9 PublishSubject<Object> subject = PublishSubject.create();
373. Subject are Observers and Observables at the same time Malte Bucksch 10 PublishSubject<Object> subject = PublishSubject.create(); subject.subscribe(new Observer<Object>() { public void onSubscribe(Disposable d) { } public void onNext(Object o) { } public void onError(Throwable e) { } public void onComplete() { } }); Subscribing to a Subject
374. Subject are Observers and Observables at the same time Malte Bucksch 11 PublishSubject<Object> subject = PublishSubject.create(); subject.subscribe(new Observer<Object>() { public void onSubscribe(Disposable d) { } public void onNext(Object o) { } public void onError(Throwable e) { } public void onComplete() { } }); otherObservable.subscribe(subject); Register Subject as an Observer
375. Subject are Observers and Observables at the same time Malte Bucksch 12 PublishSubject<Object> subject = PublishSubject.create(); subject.subscribe(new Observer<Object>() { public void onSubscribe(Disposable d) { } public void onNext(Object o) { } public void onError(Throwable e) { } public void onComplete() { } }); otherObservable.subscribe(subject); subject.onNext("Value"); subject.onError(new IllegalStateException()); subject.onComplete(); Manually inserting values into the subject
376. PublishSubject: Example Malte Bucksch 13 PublishSubject<Object> subject = PublishSubject.create();
377. PublishSubject: Example Malte Bucksch 14 PublishSubject<Object> subject = PublishSubject.create(); subject.subscribe(observer1); subject.onNext("one"); subject.onNext("two");
378. PublishSubject: Example Malte Bucksch 15 PublishSubject<Object> subject = PublishSubject.create(); // observer1 will receive all onNext and onComplete events subject.subscribe(observer1); subject.onNext("one"); subject.onNext("two");
379. PublishSubject: Example Malte Bucksch 16 PublishSubject<Object> subject = PublishSubject.create(); // observer1 will receive all onNext and onComplete events subject.subscribe(observer1); subject.onNext("one"); subject.onNext("two"); subject.subscribe(observer2); subject.onNext("three"); subject.onComplete();
380. PublishSubject: Example Malte Bucksch 17 PublishSubject<Object> subject = PublishSubject.create(); // observer1 will receive all onNext and onComplete events subject.subscribe(observer1); subject.onNext("one"); subject.onNext("two"); // observer2 will only receive "three" and onComplete subject.subscribe(observer2); subject.onNext("three"); subject.onComplete();
381. BehaviorSubject Malte Bucksch 18
382. BehaviorSubject Malte Bucksch 19
383. BehaviorSubject: Example 1 Malte Bucksch 20 BehaviorSubject<Object> subject = BehaviorSubject.createDefault("default");
384. BehaviorSubject: Example 1 Malte Bucksch 21 BehaviorSubject<Object> subject = BehaviorSubject.createDefault("default"); subject.subscribe(observer); subject.onNext("one"); subject.onNext("two"); subject.onNext("three");
385. BehaviorSubject: Example 1 Malte Bucksch 22 // observer will receive all 4 events (including "default"). BehaviorSubject<Object> subject = BehaviorSubject.createDefault("default"); subject.subscribe(observer); subject.onNext("one"); subject.onNext("two"); subject.onNext("three");
386. BehaviorSubject: Example 2 Malte Bucksch 23 BehaviorSubject<Object> subject = BehaviorSubject.create(); subject.onNext("zero"); subject.onNext("one"); subject.subscribe(observer); subject.onNext("two"); subject.onNext("three");
387. BehaviorSubject: Example 2 Malte Bucksch 24 // observer will receive the "one", "two" and "three" events, but not "zero" BehaviorSubject<Object> subject = BehaviorSubject.create(); subject.onNext("zero"); subject.onNext("one"); subject.subscribe(observer); subject.onNext("two"); subject.onNext("three");
388. BehaviorSubject: Example 3 Malte Bucksch 25 BehaviorSubject<Object> subject = BehaviorSubject.create(); subject.onNext("zero"); subject.onNext("one"); subject.onComplete(); subject.subscribe(observer);
389. BehaviorSubject: Example 3 Malte Bucksch 26 // observer will receive only onComplete BehaviorSubject<Object> subject = BehaviorSubject.create(); subject.onNext("zero"); subject.onNext("one"); subject.onComplete(); subject.subscribe(observer);
390. BehaviorSubject: Example 4 Malte Bucksch 27 BehaviorSubject<Object> subject = BehaviorSubject.create(); subject.onNext("zero"); subject.onNext("one"); subject.onError(new RuntimeException("error")); subject.subscribe(observer);
391. BehaviorSubject: Example 4 Malte Bucksch 28 // observer will receive only onError BehaviorSubject<Object> subject = BehaviorSubject.create(); subject.onNext("zero"); subject.onNext("one"); subject.onError(new RuntimeException("error")); subject.subscribe(observer);
392. Summary: Subject • Subjects are Observables and Observers at the same time • PublishSubjects is the “standard-case” emitting exactly what it observes • There are other variants like BehaviourSubjects which can come handy sometimes • Most often a Subject is NOT what you need and should be used only if you have good reasons for it Malte Bucksch 29
393. Questions so far? Malte Bucksch 30
394. ReplaySubject Malte Bucksch 31
395. AsyncSubject Malte Bucksch 32
396. Training Agenda • Part 1: RxJava Background and Overview • Part 2: RxJava Basics • Part 3: RxJava Operators • Part 4: Example of a modern UI architecture with RxJava • Part 5: Testing with RxJava • Part 6: RxJava Advanced Malte Bucksch 1
397. Part 5: Example of a modern UI architecture with RxJava Malte Bucksch 2
398. Modern Architecture with RxJava: MVVM I. The problem we’re solving II. Basic concept of MVVM III. How to use RxJava to implement a functional reactive App- Architecture IV. Testing with MVVM and RxJava V. Reusability of ViewModels Malte Bucksch 3
399. Malte Bucksch 4 TEAM Testable Sharing logic between Android and iOS Beautiful native UI Awesome app Robust & Bug-free
400. Malte Bucksch 5 TEAM Mixing business logic and view logic Testable Beautiful native UI Awesome app Sharing logic between Android and iOS Robust & Bug-free
401. The problem Malte Bucksch 6
402. MVC: Model-View-Controller Stefan Kofler & Malte Bucksch 7
403. “Model View Controller (MVC) is one of the most quoted (and most misquoted) patterns around” – Martin Fowler (martinfowler.com) Stefan Kofler & Malte Bucksch 8
404. What is MVC after all? Stefan Kofler & Malte Bucksch 9 Wikipedia Apple Martin Fowler
405. Common practice with MVC Stefan Kofler & Malte Bucksch 10 View View Controller Fragment ViewController
406. Malte Bucksch 11
407. MVVM: Model-View-ViewModel Malte Bucksch 12
408. MVVM: Model-View-ViewModel Malte Bucksch 13 View View Model Model Presentation User Input Business Logic Data User action Update Update Notify
409. Malte Bucksch 14 Data View ViewModel
410. Reactive approach with MVVM Malte Bucksch 15
411. Our approach with MVVM • Platform-independent ViewModels • Functional core using Input-to-Output mapping Malte Bucksch 16
412. MVVM – 1:1 Malte Bucksch 17 View ViewModel View ViewModel
413. MVVM Malte Bucksch 18 View ViewModel View ViewModel
414. I have a dream today! Malte Bucksch 19
415. Goal: Sharing logic between native apps Malte Bucksch 20
416. I have a dream today Malte Bucksch 21 View ViewModel View
417. I have a dream today Malte Bucksch 22 View ViewModel View ViewModel
418. Let’s build a translation app Malte Bucksch 23
419. Let’s build a translation app Malte Bucksch 24 Deactivated
420. View Models Malte Bucksch 25 View View Model Inputs Outputs
421. Malte Bucksch 26 ViewModel Translate Input Output Combine with german text Input Output
422. f(input) = output f(english) = german Malte Bucksch 27
423. ViewModel Implementation Example Malte Bucksch 28
424. ViewModel Implementation Malte Bucksch 29 ReactiveX RxJava / RxSwift
425. ViewModel with Subject as Input Malte Bucksch 30 TranslatorViewModel Subject Observer Observable Observable Input Output
426. ViewModel Interface 31 public interface TranslatorViewModel { } Malte Bucksch
427. ViewModel Interface 32 public interface TranslatorViewModel { // --- inputs Observer<String> inputEnglishText(); Observer<Boolean> inputSaveTrigger(); } Malte Bucksch
428. ViewModel Interface 33 public interface TranslatorViewModel { // --- inputs Observer<String> inputEnglishText(); Observer<Boolean> inputSaveTrigger(); // --- outputs Observable<String> outputGermanText(); Observable<Boolean> outputIsSavingAllowed(); Observable<String> outputSavedGermanTranslation(); } Malte Bucksch
429. ViewModel Implementation Malte Bucksch 34 public class TranslatorViewModelImpl implements TranslatorViewModel { }
430. ViewModel Implementation Malte Bucksch 35 public class TranslatorViewModelImpl implements TranslatorViewModel { private final BehaviorSubject<String> inputEnglishText = BehaviorSubject.createDefault(""); private final PublishSubject<Boolean> inputSaveTrigger = PublishSubject.create(); // --- inputs public BehaviorSubject<String> inputEnglishText() { return inputEnglishText; } public PublishSubject<Boolean> inputSaveTrigger() { return inputSaveTrigger; } }
431. ViewModel Implementation Malte Bucksch 36 public class TranslatorViewModelImpl implements TranslatorViewModel { private final BehaviorSubject<String> inputEnglishText = BehaviorSubject.createDefault(""); private final PublishSubject<Boolean> inputSaveTrigger = PublishSubject.create(); // --- inputs public BehaviorSubject<String> inputEnglishText() { return inputEnglishText; } public PublishSubject<Boolean> inputSaveTrigger() { return inputSaveTrigger; } // --- outputs public Observable<String> outputGermanText() { return inputEnglishText() .map(TranslatorEngine::translateToGerman); } }
432. ViewModel Implementation Malte Bucksch 37 public class TranslatorViewModelImpl implements TranslatorViewModel { private final BehaviorSubject<String> inputEnglishText = BehaviorSubject.createDefault(""); private final PublishSubject<Boolean> inputSaveTrigger = PublishSubject.create(); // --- inputs public BehaviorSubject<String> inputEnglishText() { return inputEnglishText; } public PublishSubject<Boolean> inputSaveTrigger() { return inputSaveTrigger; } // --- outputs public Observable<String> outputGermanText() { return inputEnglishText() .map(TranslatorEngine::translateToGerman); } public Observable<Boolean> outputIsSavingAllowed() { return inputEnglishText() .map(english -> !english.isEmpty()); } }
433. ViewModel Implementation Malte Bucksch 38 public class TranslatorViewModelImpl implements TranslatorViewModel { private final BehaviorSubject<String> inputEnglishText = BehaviorSubject.createDefault(""); private final PublishSubject<Boolean> inputSaveTrigger = PublishSubject.create(); // --- inputs public BehaviorSubject<String> inputEnglishText() { return inputEnglishText; } public PublishSubject<Boolean> inputSaveTrigger() { return inputSaveTrigger; } // --- outputs public Observable<String> outputGermanText() { return inputEnglishText() .map(TranslatorEngine::translateToGerman); } public Observable<Boolean> outputIsSavingAllowed() { return inputEnglishText() .map(english -> !english.isEmpty()); } public Observable<String> outputSavedGermanTranslation() { return inputSaveTrigger() .withLatestFrom(outputGermanText(), (trigger, germanText) -> germanText); } }
434. Binding to ViewModels via Java Fragment Malte Bucksch 39 // *** subscribe to inputs *** // *** subscribe to outputs ***
435. Binding to ViewModels via Java Fragment Malte Bucksch 40 // *** subscribe to inputs *** RxTextView.textChanges(englishTextView) .subscribe(text -> translatorViewModel.inputEnglishText() .onNext(text)); // *** subscribe to outputs ***
436. Binding to ViewModels via Java Fragment Malte Bucksch 41 // *** subscribe to inputs *** RxTextView.textChanges(englishTextView) .subscribe(text -> translatorViewModel.inputEnglishText() .onNext(text)); RxView.clicks(saveButton) .subscribe(v -> translatorViewModel.inputSaveTrigger() .onNext(true)); // *** subscribe to outputs ***
437. Binding to ViewModels via Java Fragment Malte Bucksch 42 // *** subscribe to inputs *** RxTextView.textChanges(englishTextView) .subscribe(text -> translatorViewModel.inputEnglishText() .onNext(text)); RxView.clicks(saveButton) .subscribe(v -> translatorViewModel.inputSaveTrigger() .onNext(true)); // *** subscribe to outputs *** translatorViewModel.outputGermanText() .subscribe(germanEditText::setText);
438. Binding to ViewModels via Java Fragment Malte Bucksch 43 // *** subscribe to inputs *** RxTextView.textChanges(englishTextView) .subscribe(text -> translatorViewModel.inputEnglishText() .onNext(text)); RxView.clicks(saveButton) .subscribe(v -> translatorViewModel.inputSaveTrigger() .onNext(true)); // *** subscribe to outputs *** translatorViewModel.outputGermanText() .subscribe(germanEditText::setText); translatorViewModel.outputIsSavingAllowed() .subscribe(saveButton::setEnabled); translatorViewModel.outputSavedGermanTranslation() .subscribe(this::saveToClipboard);
439. Binding to ViewModels via Java Fragment Malte Bucksch 44 // *** subscribe to inputs *** RxTextView.textChanges(englishTextView) .subscribe(text -> translatorViewModel.inputEnglishText() .onNext(text)); RxView.clicks(saveButton) .subscribe(v -> translatorViewModel.inputSaveTrigger() .onNext(true)); // *** subscribe to outputs *** translatorViewModel.outputGermanText() .subscribe(germanEditText::setText); translatorViewModel.outputIsSavingAllowed() .subscribe(saveButton::setEnabled); translatorViewModel.outputSavedGermanTranslation() .subscribe(this::saveToClipboard);
440. View Models Malte Bucksch 45 View View Model Input Output
441. View Model Tests Malte Bucksch 46 Unit Test View Model Input Output
442. ViewModel Tests Malte Bucksch 47 @Test public void testTranslation() { // given TranslatorViewModel translatorViewModel = new TranslatorViewModelImpl(); // when // then }
443. ViewModel Tests Malte Bucksch 48 @Test public void testTranslation() { // given TranslatorViewModel translatorViewModel = new TranslatorViewModelImpl(); TestObserver<String> testObserver = translatorViewModel.outputGermanText().test(); // when // then }
444. ViewModel Tests Malte Bucksch 49 @Test public void testTranslation() { // given TranslatorViewModel translatorViewModel = new TranslatorViewModelImpl(); TestObserver<String> testObserver = translatorViewModel.outputGermanText().test(); // when translatorViewModel.inputEnglishText().onNext("Dog"); // then }
445. ViewModel Tests Malte Bucksch 50 @Test public void testTranslation() { // given TranslatorViewModel translatorViewModel = new TranslatorViewModelImpl(); TestObserver<String> testObserver = translatorViewModel.outputGermanText().test(); // when translatorViewModel.inputEnglishText().onNext("Dog"); // then testObserver.assertValueAt(testObserver.valueCount()-1,"Hund"); }
446. Local unit tests for UI testing Malte Bucksch 51 Fast local unit tests Avoid UI testing frameworks
447. ViewModel reusability Malte Bucksch 52
448. ViewModel reusability Malte Bucksch 53 Android View View Model Input Output
449. ViewModel reusability Malte Bucksch 54 Android Fragment View Model Input Output
450. ViewModel reusability Malte Bucksch 55 Unit Test View Model Input Output
451. ViewModel reusability Malte Bucksch 56 JavaFX View View Model Input Output
452. ViewModel reusability Malte Bucksch 57 Java/Kotlin REST API View Model Input Output
453. ViewModel reusability Malte Bucksch 58 Kotlinx (HTML) View View Model Input Output
454. One ViewModel to rule them all Malte Bucksch 59
455. Wrap up: MVVM • Clear separation of concerns • Slim Views and slim ViewModels instead of massive all-in-one class • Logic can be reused on different platforms • Functional way of writing UI with isolated side effects • Bugs often prevented • Great testability • Asynchronous code that is thread-safe Malte Bucksch 60
456. Questions so far? Malte Bucksch 61
457. Hacking: Login-Screen Malte Bucksch 62
458. Hacking • Task: Implement a Login-Screen using MVVM • Open the package “exercise6_mvvm_ui and resolve TODOs in the LoginViewModelImpl HINT: you can orient at the Translator example-ViewModel Observable.combineLatest(x,y, (lastX, lastY) -> lastX + lastY) Malte Bucksch 63
459. Training Agenda • Part 1: RxJava Background and Overview • Part 2: RxJava Basics • Part 3: RxJava Operators • Part 4: Example of a modern UI architecture with RxJava • Part 5: Testing with RxJava • Part 6: RxJava Advanced Malte Bucksch 1
460. Part 5: Testing with RxJava Malte Bucksch 2
461. Testing async code without RxJava Malte Bucksch 3 @Test public void testMultiplyLargeList() { // given List<Integer> numbers = Arrays.asList(1, 2, 3); // when CountDownLatch mutex = new CountDownLatch(1); List<Integer> doubledNumbers = new ArrayList<>(); multiplyLargeList(numbers, 2, multipliedNumbers -> { doubledNumbers.addAll(multipliedNumbers); mutex.countDown(); }); mutex.await(); // then assertEquals(2, (int) doubledNumbers.get(0)); assertEquals(4, (int) doubledNumbers.get(1)); assertEquals(6, (int) doubledNumbers.get(2)); }
462. Testing async code with RxJava Malte Bucksch 4 @Test public void multiplyLargeList() { // given List<Integer> numbers = Arrays.asList(1, 2, 3); // when Observable<Integer> doubledNumbers = multiplyLargeList(numbers, 2); // then doubledNumbers.test().assertValues(2, 4, 6); }
463. Testing with RxJava • Blocking operators • blockingSubscribe() • blockingFirst() • … • TestObserver • test() • Assertions • TestScheduler Malte Bucksch 5
464. Blocking operators: blockingLast @Test public void testLast() { Observable<String> source = Observable.just("Alpha", "Beta", "Gamma", "Delta", "Zeta"); } Malte Bucksch 6
465. Blocking operators: blockingLast @Test public void testLast() { Observable<String> source = Observable.just("Alpha", "Beta", "Gamma", "Delta", "Zeta"); String lastWithLengthFour = … assertTrue(lastWithLengthFour.equals("Zeta")); } Malte Bucksch 7
466. Blocking operators: blockingLast @Test public void testLast() { Observable<String> source = Observable.just("Alpha", "Beta", "Gamma", "Delta", "Zeta"); String lastWithLengthFour = source.filter(s -> s.length() == 4) .blockingLast(); assertTrue(lastWithLengthFour.equals("Zeta")); } Malte Bucksch 8
467. Blocking operators: blockingSubscribe @Test public void testHitCountIsFive() { Observable<Long> source = Observable.interval(1, TimeUnit.SECONDS) .take(5); } Malte Bucksch 9
468. Blocking operators: blockingSubscribe @Test public void testHitCountIsFive() { AtomicInteger hitCount = new AtomicInteger(); Observable<Long> source = Observable.interval(1, TimeUnit.SECONDS) .take(5); assertTrue(hitCount.get() == 5); } Malte Bucksch 10
469. Blocking operators: blockingSubscribe @Test public void testHitCountIsFive() { AtomicInteger hitCount = new AtomicInteger(); Observable<Long> source = Observable.interval(1, TimeUnit.SECONDS) .take(5); source.blockingSubscribe(i -> hitCount.incrementAndGet()); assertTrue(hitCount.get() == 5); } Malte Bucksch 11
470. Testing with Rx 1. Blocking-Operators 2. TestObserver Malte Bucksch 12
471. Testing if the translation works Malte Bucksch 13
472. TestObserver: Example Malte Bucksch 14 @Test public void testTranslation() { // given TranslatorViewModel translatorViewModel = new TranslatorViewModelImpl(); // when // then }
473. TestObserver: Example Malte Bucksch 15 @Test public void testTranslation() { // given TranslatorViewModel translatorViewModel = new TranslatorViewModelImpl(); TestObserver<String> testObserver = translatorViewModel.outputGermanText().test(); // when // then }
474. TestObserver: Example Malte Bucksch 16 @Test public void testTranslation() { // given TranslatorViewModel translatorViewModel = new TranslatorViewModelImpl(); TestObserver<String> testObserver = translatorViewModel.outputGermanText().test(); // when translatorViewModel.inputEnglishText().onNext("Dog"); // then }
475. TestObserver: Example Malte Bucksch 17 @Test public void testTranslation() { // given TranslatorViewModel translatorViewModel = new TranslatorViewModelImpl(); TestObserver<String> testObserver = translatorViewModel.outputGermanText().test(); // when translatorViewModel.inputEnglishText().onNext("Dog"); // then testObserver.assertValueAt(testObserver.valueCount()-1,"Hund"); } Last value received
476. TestObserver: Example Malte Bucksch 18 @Test public void testTranslation() { // given TranslatorViewModel translatorViewModel = new TranslatorViewModelImpl(); TestObserver<String> testObserver = translatorViewModel.outputGermanText().test(); // when translatorViewModel.inputEnglishText().onNext("Dog"); // then testObserver.assertValueAt(testObserver.valueCount()-1,"Hund"); }
477. TestObserver: Example Malte Bucksch 19 @Test public void testTranslation() { // given TranslatorViewModel translatorViewModel = new TranslatorViewModelImpl(); TestObserver<String> testObserver = new TestObserver<>(); translatorViewModel.outputGermanText().subscribe(testObserver); // when translatorViewModel.inputEnglishText().onNext("Dog"); // then testObserver.assertValueAt(testObserver.valueCount()-1,"Hund"); }
478. TestObserver-Super-Powers Malte Bucksch 20 Records all values for later Assertions Assertion-Methods
479. TestObserver: Recording Malte Bucksch 21 @Test public void testTranslation() { // given TranslatorViewModel translatorViewModel = new TranslatorViewModelImpl(); TestObserver<String> testObserver = translatorViewModel.outputGermanText().test(); // when translatorViewModel.inputEnglishText().onNext("Dog"); // then testObserver.assertValueAt(testObserver.valueCount() - 1, "Dog translated"); } Starts recording…
480. TestObserver: Recording started too late Malte Bucksch 22 @Test public void testTranslation() { // given TranslatorViewModel translatorViewModel = new TranslatorViewModelImpl(); // when translatorViewModel.inputEnglishText().onNext("Dog"); TestObserver<String> testObserver = translatorViewModel.outputGermanText().test(); // then testObserver.assertValueAt(testObserver.valueCount() - 1, "Dog translated"); } Starts recording…
481. TestObserver-Methods • assertValueAt(n,value) • assertValueCount(count) • assertError(error) • assertTimeout() • assertComplete() … Malte Bucksch 23
482. Questions so far? Malte Bucksch 24
483. Hacking: Testing the LoginViewModel Malte Bucksch 25
484. Training Agenda • Part 1: RxJava Background and Overview • Part 2: RxJava Basics • Part 3: RxJava Operators • Part 4: Example of a modern UI architecture with RxJava • Part 5: Testing with RxJava • Part 6: RxJava Advanced Malte Bucksch 1
485. Dealing with side effects Malte Bucksch 2
486. Operators for dealing with Side effects do.. • doOnComplete • doOnDispose • doOnEach • doOnError • doOnNext • doOnSubscribe • doOnTerminate … Malte Bucksch 3
487. Live coding: Example for printing in LoginViewModel Malte Bucksch 4
488. More useful operators: Compose Malte Bucksch 5
489. Example: Concating String Malte Bucksch 6 String separator = " "; Observable<String> concatString = Observable .just("Ich", "heiße", "Tom") … concatString.subscribe(System.out::print);
490. Example: Concating String Malte Bucksch 7 String separator = " "; Observable<String> concatString = Observable .just("Ich", "heiße", "Tom") .reduce((s, s2) -> s + separator + s2) .toObservable(); concatString.subscribe(System.out::print);
491. Example: Concating String Malte Bucksch 8 Observable<String> concatString = Observable .just("Ich", "heiße", "Tom") .compose(RxTransformers.concatStrings(" ")); concatString.subscribe(System.out::print);
492. Live coding: Example for “concatStrings” and “isEven” using “compose” Malte Bucksch 9
493. Questions so far? Malte Bucksch 10
494. Hacking: Build a custom operator with “compose” for printing the state changes of an Observable exercise7_compose_and_sideeffects Malte Bucksch 11
495. Sharing subscriptions with “share()” Malte Bucksch 12
496. Sharing subscriptions with “share()” Open exercise8_share/ShareExercise and run the main function Look at the printed output: Do you notice something strange? Malte Bucksch 13
497. Cold Observables Malte Bucksch 14 Observable<String> observable = Observable.just("A", "B", "C", "D", "E"); // observer 1 observable.subscribe(val -> { // "A", "B", "C", "D", "E" will be received in order }); // observer 2 observable.subscribe(val -> { // Again, "A", "B", "C", "D", "E" will be received in order });
498. Sharing subscriptions with “share()” Malte Bucksch 15 Observable.create(…) Subscribe() Observable.create(…) Subscribe() Observable.create(…)
499. Sharing subscriptions with “share()” Malte Bucksch 16 share() Subscribe() Observable.create(…) Subscribe()
500. Hacking: Fix the strange behaviour using “.share” exercise8_share Malte Bucksch 17
501. Questions so far? Malte Bucksch 18
502. Asynchronous Code Malte Bucksch 19
503. Quiz Malte Bucksch 20
504. What will be printed? Malte Bucksch 21 System.out.println("Creating Observable."); Observable.<String>create(emitter -> { emitter.onNext("test"); emitter.onComplete(); }).subscribe(new Observer<String>() { @Override public void onSubscribe(Disposable d) { } @Override public void onNext(String value) { System.out.println("onNext(): " + value); } @Override public void onError(Throwable e) { } @Override public void onComplete() { System.out.println("onComplete()"); } }); System.out.println("After subscribing."); Creating Observable. After subscribing onNext() - test onComplete() Creating Observable. onNext() - test onComplete() After subscribing Creating Observable. onNext() - test After subscribing onComplete() A B C
505. What will be printed? Malte Bucksch 22 System.out.println("Creating Observable."); Observable.<String>create(emitter -> { emitter.onNext("test"); emitter.onComplete(); }).subscribe(new Observer<String>() { @Override public void onSubscribe(Disposable d) { } @Override public void onNext(String value) { System.out.println("onNext(): " + value); } @Override public void onError(Throwable e) { } @Override public void onComplete() { System.out.println("onComplete()"); } }); System.out.println("After subscribing."); Creating Observable. After subscribing onNext() - test onComplete() Creating Observable. onNext() - test onComplete() After subscribing Creating Observable. onNext() - test After subscribing onComplete() A B C
506. What will be printed? Malte Bucksch 23 Observable.<String>create(emitter -> { emitter.onNext("test"); emitter.onComplete(); }).subscribe(new Observer<String>() { @Override public void onSubscribe(Disposable d) { } @Override public void onNext(String value) { System.out.println("onNext(): " + value); } @Override public void onError(Throwable e) { } @Override public void onComplete() { System.out.println("onComplete()"); } }); System.out.println("After subscribing."); “Creating Observable. onNext() - test onComplete() After subscribing”
507. More useful things for your journey Malte Bucksch 24
508. Flowable Malte Bucksch 25
509. Debugging in RxJava Malte Bucksch 26
510. Scan Malte Bucksch 27
511. Scan Malte Bucksch 28
512. Scan Malte Bucksch 29
513. Scan Malte Bucksch 30 Current time
514. Scan Malte Bucksch 31 Current time
515. Scan Malte Bucksch 32 Current time
516. Scan Malte Bucksch 33 Current time
517. Scan Malte Bucksch 34 Current time
518. Looking back on what we achieved Malte Bucksch 1
519. Looking back on what we achieved • Learned RxJava Basics as well as many advanced Rx-concepts Malte Bucksch 2
520. Looking back on what we achieved • Learned RxJava Basics as well as many advanced Rx-concepts • Learned most important Rx-Operators Malte Bucksch 3
521. Looking back on what we achieved • Learned RxJava Basics as well as many advanced Rx-concepts • Learned most important Rx-Operators • Learned how to write asynchronous code in Rx Malte Bucksch 4
522. Looking back on what we achieved • Learned RxJava Basics as well as many advanced Rx-concepts • Learned most important Rx-Operators • Learned how to write asynchronous code in Rx • Learned how to build a User interface architecture with RxJava Malte Bucksch 5
523. Looking back on what we achieved • Learned RxJava Basics as well as many advanced Rx-concepts • Learned most important Rx-Operators • Learned how to write asynchronous code in Rx • Learned how to build a User interface architecture with RxJava • Learned how to test asynchronous code with RxJava code Malte Bucksch 6
524. Looking back on what we achieved • Learned RxJava Basics as well as many advanced Rx-concepts • Learned most important Rx-Operators • Learned how to write asynchronous code in Rx • Learned how to build a User interface architecture with RxJava • Learned how to test asynchronous code with RxJava code • Learned tricks to make your Rx-Code look more beautiful and robust Malte Bucksch 7
525. Summary: RxJava - Advantages • makes managing asynchronous data flows easier • allows you to write declarative rather than imperative code • allows you to write similar code in different programming languages • makes your code more functional and predictable • makes testing of asynchronous code easier • Makes asynchronous error-handling easier • supplies many operators to solve problems more concisely • can make your application more fluent and performant by using lazy evaluation and simplifying parallelization Malte Bucksch 8
526. Summary: RxJava - Disadvantages • Steep learning curve (sophisticated library that needs to be learned + needs time to think reactive/functional rather than imperative) • Adds a dependency which the whole project is based on • Debugging is sometimes less comfortable Malte Bucksch 9
527. Getting clarity: Questions and Discussion Example topics: • Observable creation • Observable subscriptions • Observable operators • Async code and Multithreading • Single/Maybe/Completable/Subjects • Error handling • Side effects • Architecture with Rx • Testing (e.g. manipulating time with TestScheduler) Malte Bucksch 10
528. Conclusion/Opinion: RxJava is awesome Malte Bucksch 11
529. More Resources The introduction to Reactive Programming you've been missing https://gist.github.com/staltz/868e7e9bc2a7b8c1f754 Interactive Rx-Marbles Diagrams http://rxmarbles.com/ Great book about Rx (for free) http://www.introtorx.com/ Book: https://www.amazon.de/Learning-RxJava-Concurrent-responsive- applications/dp/1787120422/ref=sr_1_1?ie=UTF8&qid=1529678994&sr=8- 1&keywords=rxjava+nield More: https://github.com/ReactiveX/RxJava/wiki/Additional-Reading Malte Bucksch 12
530. Other trainings that I offer Malte Bucksch 13 Rx-Trainings App-Architecture Trainings MVVM Kotlin Trainings
531. Hope you learned something!  Malte Bucksch 14