LiveData<🤖> vs Observable<Rx> vs Channel<Kt> (minimal slides)

All these classes can be used to handle a flow of data in your Android app. This presentation goes through a specific use case, and how these classes differ in their implementations of managing and observing data.

Transcript

1. LiveData< > vs Observable< > vs Channel< >
2. Jacques Smuts • ??? • 2014 - Started Coding Android • 2018 - Started Coding Kotlin + RxJava • 2019 - Started Using Coroutines + LiveData @JacquesSmuts GDG Cape Town JacquesSmuts.com
3. REACTIVE PROGRAMMING !
4. Observable Observer Emit
5. Observable/Publisher/Emitter/Subject/Channel/Flowable Observer/Subscriber/Disposable/Receiver/Consumer/Collector Emit/Publish/ Send/Broadcast
6. Observable< > vs Database Observable< > vs Binding Observable< > vs Observable< > vs Flow< > vs LiveData Observable< > vs Observable< > vs
7. 3 Observables • LiveData<T> • io.reactivex.Observable<T> • kotlinx.coroutines.channels.Channel<T> Flow<T> Flowable<T> equivalenty related
8. LiveData< >
9. LiveData< > • Built into Android AppCompat Library • Is meant to provide up-to-date data to UI • Tied to Activity/Fragment lifecycle to prevent leaks/crashes • Reliable, easy, simple • Good for beginners
10. LiveData< > • Built into Android AppCompat Library • Is meant to provide up-to-date data to UI • Tied to Activity/Fragment lifecycle to prevent leaks/crashes • Reliable, easy, simple • Good for beginners
11. Activity/ Fragment (onCreate) Hardcoded URL The Worst Way get Email email@ address.com
12. Slightly Better Activity/ Fragment (onCreate) API Service ViewModel Repository (Database) get Email oldEmail@ address.com get Email newEmail@ address.com newEmail@ address.com
13. LiveData<> Activity/ Fragment (onCreate) API Service Repository (Database) LiveData oldEmail@ address.com newEmail@ address.com ViewModel update Email
14. LiveData<> Observer class UserFragment/Activity { override fun onCreate(savedInstanceState: Bundle?) { } }
15. LiveData<> Observer class UserFragment/Activity { override fun onCreate(savedInstanceState: Bundle?) { userViewModel.liveEmail.observe(this, Observer { email -> updateUi(email) }) } } LifecycleOwner null? val liveEmail: LiveData<String>
16. LiveData<> Observer class UserFragment/Activity { override fun onCreate(savedInstanceState: Bundle?) { userViewModel.liveEmail.observeNonNull(this) { email -> updateUi(email) }) } }
17. LiveData<> Activity/ Fragment (onCreate) API Service Repository (Database) LiveData newEmail@ address.com ViewModel
18. LiveData<> Observable class UserViewModel { val liveEmail: LiveData<String> = ? }
19. class UserViewModel { val roomDatabaseRepository = RoomDatabaseRepository .getInstance() val liveEmail: LiveData<String> get() = roomDatabaseRepository.getLiveEmail() } LiveData<> Observable
20. class UserViewModel { val _liveEmail = MutableLiveData<String>() } LiveData<> Observable
21. class UserViewModel { val _liveEmail = MutableLiveData<String>() fun updateEmail(email: String) { _liveEmail.postValue(email) } } Automatically on UI Thread LiveData<> Observable liveEmail.value == [last value]
22. class UserViewModel { private val _liveEmail = MutableLiveData<String>() val liveEmail: LiveData<String> get() = liveEmailMutable fun updateEmail(email: String) { _liveEmail.postValue(email) } } LiveData<> Observable
23. LiveData<> Activity/ Fragment (onCreate) API Service Repository (Database) LiveData oldEmail@ address.com newEmail@ address.com ViewModel update Email
24. LiveData<> Activity/ Fragment (onDestroy) API Service Repository (Database) LiveData ViewModel newEmail@ address.com
25. Observable< >
27. Observable< > • Difficult to understand at first • Large Library • Long History • Powerful and can adapt to any situation
28. Observable< > • Difficult to understand at first • Large Library • Long History • Powerful and can adapt to any situation
29. RxJava Activity/ Fragment (onStart) API Service Repository (Database) Observable ViewModel update Email oldEmail@ address.com State SERVER newEmail@ address.com
30. RxJava Observer class UserFragment/Activity { override fun onCreate(savedInstanceState: Bundle?) { } }
31. class AnyClass { init { } } RxJava Observer
32. class UserFragment/Activity { override fun onCreate(savedInstanceState: Bundle?) { } } RxJava Observer
33. class UserFragment/Activity { override fun onCreate(savedInstanceState: Bundle?) { userViewModel.observableState .subscribe { state -> updateUi(state) } } } RxJava Observer
34. class UserFragment/Activity { override fun onCreate(savedInstanceState: Bundle?) { userViewModel.observableState .subscribe { state -> updateUi(state) }, { error -> logError(error) } } } Semi-auto error catching RxJava Observer
35. class UserFragment/Activity { override fun onCreate(savedInstanceState: Bundle?) { userViewModel.observableState .throttleLast(100, TimeUnit.Milliseconds) .subscribe { state -> updateUi(state) }, { error -> logError(error) } } } RxJava Observer
36. class UserFragment/Activity { override fun onCreate(savedInstanceState: Bundle?) { userViewModel.observableState .distinctUntilChanged() .subscribe { state -> updateUi(state) }, { error -> logError(error) } } } RxJava Observer
37. class UserFragment/Activity { override fun onCreate(savedInstanceState: Bundle?) { userViewModel.observableState .subscribe { state -> updateUi(state) }, { error -> logError(error) } } } RxJava Observer
38. class UserFragment/Activity { val disposables = CompositeDisposable() override fun onCreate(savedInstanceState: Bundle?) { disposables.add(userViewModel.observableState .subscribe { state -> updateUi(state.email) }, { error -> logError(error) }) } } disposables.clear() RxJava Observer
39. RxJava Activity/ Fragment (onStart) API Service Repository (Database) Observable ViewModel oldEmail@ address.com State
40. RxJava Observable class UserViewModel { val observableEmail: Observable<String> = ? }
41. class UserViewModel { val roomDatabaseRepository = RoomDatabaseRepository .getInstance() val observableEmail: Flowable<String> get() = roomDatabaseRepository.getEmail() } Observable<String> RxJava Observable
42. class UserViewModel { val _stateObservable = PublishSubject<State>() } RxJava Observable Does not retain State
43. class UserViewModel { val _stateObservable = PublishSubject<State>() fun updateState(email: String) { _stateObservable.onNext(State(email)) } } RxJava Observable
44. class UserViewModel { private val _stateObservable = PublishSubject<State>() val stateObservable get()= _stateObservable.hide() fun updateState(email: String) { _stateObservable.onNext(State(email)) } } RxJava Observable
45. RxJava Activity/ Fragment (onStart) API Service Repository (Database) Observable ViewModel update Email oldEmail@ address.com State SERVER newEmail@ address.com
46. RxJava Activity/ Fragment (onStop) API Service Repository (Database) ViewModel newEmail@ address.com Observable State
47. Channel< >/Flow
48. Channel< >/Flow • Experimental • Amazing community • Readable Code • One small part of Coroutines Library • Is The Future
49. Channel< >/Flow • Experimental • Amazing community • Readable Code • One small part of Coroutines Library • Is The Future
50. Channel/Flow Activity/ Fragment (onCreate) API Service Repository (Database) Flow ViewModel update Email oldEmail@ address.com State SERVER newEmail@ address.com
51. Channel/Flow Observer class UserFragment/Activity { override fun onCreate(savedInstanceState: Bundle?) { } }
52. Channel/Flow Observer class UserFragment/Activity, CoroutineScope by MainScope() { override fun onCreate(savedInstanceState: Bundle?) { } }
53. Channel/Flow Observer class UserFragment/Activity, CoroutineScope by MainScope() { override fun onCreate(savedInstanceState: Bundle?) { launch { } } }
54. Channel/Flow Observer class UserFragment/Activity, CoroutineScope by MainScope() { override fun onCreate(savedInstanceState: Bundle?) { launch { userViewModel.stateFlow .collect { state -> updateUi(state) } } } } All coroutines in scope cleaned up by 
 coroutineContext.cancelChildren()
55. Channel/Flow Observer class UserFragment/Activity, CoroutineScope by MainScope() { override fun onCreate(savedInstanceState: Bundle?) { launch { userViewModel.stateFlow .throttleLast(100, TimeUnit.Millisecond) .collect { state -> updateUi(state) } } } }
56. Channel/Flow Observer class UserFragment/Activity, CoroutineScope by MainScope() { override fun onCreate(savedInstanceState: Bundle?) { launch { userViewModel.stateFlow .debounce() .collect { state -> updateUi(state) } } } }
57. Channel/Flow Observer class UserFragment/Activity, CoroutineScope by MainScope() { override fun onCreate(savedInstanceState: Bundle?) { launch { userViewModel.stateFlow .distinctUntilChanged() .collect { state -> updateUi(state) } } } }
58. Channel/Flow Activity/ Fragment (onCreate) API Service Repository (Database) Flowable ViewModel State
59. Coroutines Observable class UserViewModel { val emailFlow: Flow<String> = ? }
60. class UserViewModel { val roomDatabaseRepository = RoomDatabaseRepository .getInstance() val emailFlow: Flow<String> get() = roomDatabaseRepository.getEmail() } Coroutines Observable
61. class UserViewModel { val stateObservable = BroadcastChannel<State>(1) } Coroutines Observable Capacity of 1
62. class UserViewModel { val stateObservable = BroadcastChannel<State>(1) fun updateState(email: String) { stateObservable.offer(State(email)) } } Coroutines Observable Returns true/false, yeets exception
63. class UserViewModel, CoroutineScope by DefaultScope() { val stateObservable = BroadcastChannel<State>(1) fun updateState(email: String) { stateObservable.offer(State(email)) } } Coroutines Observable
64. class UserViewModel, CoroutineScope by DefaultScope() { val stateObservable = BroadcastChannel<State>(1) fun updateState(email: String) { launch { stateObservable.send(State(email)) } } } Coroutines Observable
65. class UserViewModel, CoroutineScope by DefaultScope() { val stateObservable = BroadcastChannel<State>(1) fun updateState(email: String) { stateObservable.offer(State(email)) } } Coroutines Observable
66. class UserViewModel, CoroutineScope by DefaultScope() { private val _stateObservable = BroadcastChannel<State>(1) val stateObservable get()= _stateObservable.asFlow() fun updateState(email: String) { _stateObservable.offer(State(email)) } } Coroutines Observable Channels inside, Flows outside
67. Channel/Flow Activity/ Fragment (onCreate) API Service Repository (Database) Flowable ViewModel update Email oldEmail@ address.com State SERVER newEmail@ address.com
68. Channel/Flow Activity/ Fragment (onDestroy) API Service Repository (Database) Flowable ViewModel State newEmail@ address.com
69. Comparisons LiveData Easy to Read Yes Lifecycle/Cleanup Fully Auto Nullable Always Scope UI Only Saves Last Value Yes Threading UI Only Stable / Reliable Yes Guides / Docs Good Multiplatform No
70. Comparisons LiveData RxJava Easy to Read Yes No Lifecycle/Cleanup Fully Auto Fully Manual Nullable Always Configurable Scope UI Only Anywhere Saves Last Value Yes Configurable Threading UI Only Mostly Easy Stable / Reliable Yes Yes Guides / Docs Good Meh Multiplatform No Sorta
71. Comparisons LiveData RxJava Coroutines Easy to Read Yes No Mostly Lifecycle/Cleanup Fully Auto Fully Manual Semi-Auto Nullable Always Configurable IDE-enforced Scope UI Only Anywhere Anywhere Saves Last Value Yes Configurable Configurable Threading UI Only Mostly Easy Easy Stable / Reliable Yes Yes Sorta Guides / Docs Good Meh Quality, but few Multiplatform No Sorta Mostly
72. Comparisons LiveData RxJava Coroutines Easy to Read Lifecycle/Cleanup Nullable Scope Saves Last Value Threading Stable / Reliable Guides / Docs Multiplatform ⏳ ⏳
73. Comparisons LiveData RxJava Coroutines Who should use it? Beginners++ Intermediate++ Everyone* Final Rating Team Setup? Small / New Large Production App Supportive team Any setup* All Future Kotlin Apps ⏳ *Willing to accept risk of cutting edge
74. Questions
75. Testing LiveData RxJava Coroutines Ease of basic testing Easy Almost easy Easy Ease of complex testing ? Doable Doable Readability of Tests Easy Almost Easy Easy