I Wrote an App with Architecture Components

Architecture Components were announced to much fanfare at Google I/O 2017, as it finally gave Android developers some official guidance on how to architect their applications. It also gave us tools to make managing lifecycle changes much easier, and to persist data without writing lots of annoying SQLite boilerplate code. By now we’ve all read the documentation and tutorials, but how easy is it to use these intriguing new tools in a production application? (Spoiler alert: they’re pretty helpful)

I developed an app from scratch using all of the new Architecture Components – ViewModels and an MVVM architecture, Room to persist all the local data, and LiveData objects to easily and safely update the UI with automatic lifecycle handling. Join us as we discuss in detail what it’s like to use these new Architecture Components in a real world situation – we’ll talk about the problems they solved, the problems they created, and whether or not they’re the right choice for your next project.

Transcript

1. Phil Shadlyn @physphil I Wrote an App with Architecture Components
2. Architecture Components
3. - Google “A collection of libraries that help you design robust, testable, and maintainable apps.”
4. https://developer.android.com/topic/libraries/architecture/guide.html
5. LiveData https://developer.android.com/topic/libraries/architecture/guide.html
6. LiveData ViewModels https://developer.android.com/topic/libraries/architecture/guide.html
7. LiveData ViewModels Room https://developer.android.com/topic/libraries/architecture/guide.html
8. LiveData ViewModels Room Paging Library https://developer.android.com/topic/libraries/architecture/guide.html
9. Don’t listen to me.
10. Don’t only listen to me.
11. A Simple Reminder App
12. ViewModel
 - Hold view data - React to user input Room
 - Retrieves data from SQLite - Push updates to LiveData ReminderRepo.kt LiveData Exposed methods
13. ViewModel
 - Hold view data - React to user input Room
 - Retrieves data from SQLite - Push updates to LiveData ReminderRepo.kt LiveData Exposed methods
14. LiveData
15. LiveData
16. • Subscribe for data updates LiveData
17. • Subscribe for data updates • Lifecycle aware - no more unsubscribe(this) LiveData
18. • Subscribe for data updates • Lifecycle aware - no more unsubscribe(this) • MutableLiveData, SingleLiveEvent are useful subclasses LiveData
19. val reminderList: LiveData<List<Reminder>> = repo.getReminderList() MainActivityViewModel.kt
20. val reminderList: LiveData<List<Reminder>> = repo.getReminderList() override fun onCreate(savedInstanceState: Bundle?) { viewModel.reminderList.observe(this, Observer { reminders -> reminders?.let { adapter.setReminderList(it) viewModel.reminderListUpdated(it) fab.show() } }) } MainActivity.kt MainActivityViewModel.kt
21. val reminderList: LiveData<List<Reminder>> = repo.getReminderList() override fun onCreate(savedInstanceState: Bundle?) { viewModel.reminderList.observe(this, Observer { reminders -> reminders?.let { adapter.setReminderList(it) viewModel.reminderListUpdated(it) fab.show() } }) } MainActivity.kt MainActivityViewModel.kt
22. MutableLiveData
23. private val spinnerVisibility = MutableLiveData<Boolean>() private val emptyVisibility = MutableLiveData<Boolean>() MainActivityViewModel.kt
24. private val spinnerVisibility = MutableLiveData<Boolean>() private val emptyVisibility = MutableLiveData<Boolean>() MainActivityViewModel.kt // Mutable LiveData accessor methods - everyone loves ensuring immutability! fun getSpinnerVisibility(): LiveData<Boolean> = spinnerVisibility fun getEmptyVisibility(): LiveData<Boolean> = emptyVisibility
25. private val spinnerVisibility = MutableLiveData<Boolean>() private val emptyVisibility = MutableLiveData<Boolean>() MainActivityViewModel.kt // Mutable LiveData accessor methods - everyone loves ensuring immutability! fun getSpinnerVisibility(): LiveData<Boolean> = spinnerVisibility fun getEmptyVisibility(): LiveData<Boolean> = emptyVisibility fun reminderListUpdated(reminders: List<Reminder>) { spinnerVisibility.value = false emptyVisibility.value = reminders.isEmpty() }
26. SingleLiveEvent
27. // Single events - subscribe for UI updates val clearNotificationEvent = SingleLiveEvent<Int?>() val showDeleteConfirmationEvent = SingleLiveEvent<Unit>() val showDeleteAllConfirmationEvent = SingleLiveEvent<Unit>() MainActivityViewModel.kt
28. // Single events - subscribe for UI updates val clearNotificationEvent = SingleLiveEvent<Int?>() val showDeleteConfirmationEvent = SingleLiveEvent<Unit>() val showDeleteAllConfirmationEvent = SingleLiveEvent<Unit>() MainActivityViewModel.kt fun deleteAllReminders() { scheduler.cancelAllJobs() repo.deleteAllReminders() clearNotificationEvent.postValue(notificationId) }
29. Testing?
30. @Test fun testGetReminderById() { val reminder = Reminder(title = TITLE) val id = reminder.id dao.insertReminder(reminder) dao.insertReminder(Reminder()) dao.insertReminder(Reminder()) val result = LiveDataTestUtil.getValue(dao.getReminderById(id)) assertTrue(result.id == id) assertTrue(result.title == TITLE) } ReminderDaoTest.kt
31. @Test fun testGetReminderById() { val reminder = Reminder(title = TITLE) val id = reminder.id dao.insertReminder(reminder) dao.insertReminder(Reminder()) dao.insertReminder(Reminder()) val result = LiveDataTestUtil.getValue(dao.getReminderById(id)) assertTrue(result.id == id) assertTrue(result.title == TITLE) } ReminderDaoTest.kt
32. Pros
33. • Simple to implement Pros
34. • Simple to implement • Automatically updated with backing data change (from Room) Pros
35. • Simple to implement • Automatically updated with backing data change (from Room) • Lifecycle aware Pros
36. Gotchas
37. • Create getters for MutableLiveData Gotchas
38. • Create getters for MutableLiveData • SingleLiveEvent for one-time updates Gotchas
39. • Create getters for MutableLiveData • SingleLiveEvent for one-time updates • Limited compared to RxJava Gotchas
40. Should I use LiveData?
41. Should I use LiveData?
42. ViewModel
43. ViewModel
44. • Contains LiveData and logic required for view ViewModel
45. • Contains LiveData and logic required for view • React to user input ViewModel
46. • Contains LiveData and logic required for view • React to user input • Survive configuration changes! ViewModel
47. class MainActivityViewModel(private val repo: ReminderRepo, private val scheduler: JobRequestScheduler) : ViewModel() { // LiveData objects - subscribe for UI updates val reminderList: LiveData<List<Reminder>> = repo.getActiveReminders() private val spinnerVisibility = MutableLiveData<Boolean>() private val emptyVisibility = MutableLiveData<Boolean>()
48. class MainActivityViewModel(private val repo: ReminderRepo, private val scheduler: JobRequestScheduler) : ViewModel() { // LiveData objects - subscribe for UI updates val reminderList: LiveData<List<Reminder>> = repo.getActiveReminders() private val spinnerVisibility = MutableLiveData<Boolean>() private val emptyVisibility = MutableLiveData<Boolean>() // Single events - subscribe for UI updates val clearNotificationEvent = SingleLiveEvent<Int?>() val showDeleteConfirmationEvent = SingleLiveEvent<Unit>() val showDeleteAllConfirmationEvent = SingleLiveEvent<Unit>()
49. class MainActivityViewModel(private val repo: ReminderRepo, private val scheduler: JobRequestScheduler) : ViewModel() { // LiveData objects - subscribe for UI updates val reminderList: LiveData<List<Reminder>> = repo.getActiveReminders() private val spinnerVisibility = MutableLiveData<Boolean>() private val emptyVisibility = MutableLiveData<Boolean>() // Single events - subscribe for UI updates val clearNotificationEvent = SingleLiveEvent<Int?>() val showDeleteConfirmationEvent = SingleLiveEvent<Unit>() val showDeleteAllConfirmationEvent = SingleLiveEvent<Unit>() // Mutable LiveData accessor methods - everyone loves ensuring immutability! fun getSpinnerVisibility(): LiveData<Boolean> = spinnerVisibility fun getEmptyVisibility(): LiveData<Boolean> = emptyVisibility
50. class MainActivityViewModel(private val repo: ReminderRepo, private val scheduler: JobRequestScheduler) : ViewModel() { // LiveData objects - subscribe for UI updates val reminderList: LiveData<List<Reminder>> = repo.getActiveReminders() private val spinnerVisibility = MutableLiveData<Boolean>() private val emptyVisibility = MutableLiveData<Boolean>() // Single events - subscribe for UI updates val clearNotificationEvent = SingleLiveEvent<Int?>() val showDeleteConfirmationEvent = SingleLiveEvent<Unit>() val showDeleteAllConfirmationEvent = SingleLiveEvent<Unit>() // Mutable LiveData accessor methods - everyone loves ensuring immutability! fun getSpinnerVisibility(): LiveData<Boolean> = spinnerVisibility fun getEmptyVisibility(): LiveData<Boolean> = emptyVisibility // Public user-driven methods fun reminderListUpdated(reminders: List<Reminder>) { spinnerVisibility.value = false emptyVisibility.value = reminders.isEmpty() } fun confirmDeleteAllReminders() { showDeleteAllConfirmationEvent.call() } fun deleteAllReminders() { scheduler.cancelAllJobs() repo.deleteAllReminders() clearNotificationEvent.call() }
51. override fun onCreate(savedInstanceState: Bundle?) { viewModel = ViewModelProviders.of(this, MainActivityViewModelFactory(repo, scheduler)) .get(MainActivityViewModel::class.java) } MainActivity.kt
52. class MainActivityViewModelFactory(private val repo: ReminderRepo, private val scheduler: JobRequestScheduler) : ViewModelProvider.Factory { override fun <T : ViewModel> create(modelClass: Class<T>): T { if (modelClass.isAssignableFrom(MainActivityViewModel::class.java)) { return MainActivityViewModel(repo, scheduler) as T } throw IllegalArgumentException("Cannot instantiate ViewModel class with those arguments") } } MainActivityViewModelFactory.kt override fun onCreate(savedInstanceState: Bundle?) { viewModel = ViewModelProviders.of(this, MainActivityViewModelFactory(repo, scheduler)) .get(MainActivityViewModel::class.java) } MainActivity.kt
53. class MainActivityViewModelFactory(private val repo: ReminderRepo, private val scheduler: JobRequestScheduler) : ViewModelProvider.Factory { override fun <T : ViewModel> create(modelClass: Class<T>): T { if (modelClass.isAssignableFrom(MainActivityViewModel::class.java)) { return MainActivityViewModel(repo, scheduler) as T } throw IllegalArgumentException("Cannot instantiate ViewModel class with those arguments") } } MainActivityViewModelFactory.kt override fun onCreate(savedInstanceState: Bundle?) { viewModel = ViewModelProviders.of(this, MainActivityViewModelFactory(repo, scheduler)) .get(MainActivityViewModel::class.java) } MainActivity.kt
54. … and, Testing?
55. @Test fun testReminderListUpdated() { val reminders = listOf(Reminder(), Reminder()) `when`(repo.getActiveReminders()).thenReturn(Flowable.just(reminders)) viewModel = MainActivityViewModel(repo, scheduler) viewModel.reminderListUpdated(reminders) viewModel.getSpinnerVisibility().observeForever({ assertEquals(it, false) }) viewModel.getEmptyVisibility().observeForever({ assertEquals(it, false) }) } @Test fun testDeleteReminder() { val reminder = Reminder() viewModel.clearNotificationEvent.observeForever({ id -> assertEquals(id, reminder.notificationId) }) viewModel.confirmDeleteReminder(reminder) viewModel.deleteReminder() verify(scheduler).cancelJob(reminder.externalId) verify(repo).deleteReminder(reminder) } MainActivityViewModelTest.kt
56. Pros
57. • Android supported architecture Pros
58. • Android supported architecture • Persist config changes!! Pros
59. • Android supported architecture • Persist config changes!! • Easy JVM Tests Pros
60. Gotchas
61. Gotchas • Don’t instantiate directly
62. Gotchas • Don’t instantiate directly • Implement ViewModelProvider.Factory for constructor parameters
63. Gotchas • Don’t instantiate directly • Implement ViewModelProvider.Factory for constructor parameters • Inherit from AndroidViewModel if you need (Application) context
64. Should I use ViewModels?
65. Should I use ViewModels?
66. Room
67. Room
68. • Communicates with SQLite database Room
69. • Communicates with SQLite database • Pushes updates with LiveData or RxJava Room
70. • Communicates with SQLite database • Pushes updates with LiveData or RxJava • Access through repository Room
71. @Entity(tableName = TABLE_REMINDERS) data class Reminder(@ColumnInfo(name = REMINDER_COLUMN_TITLE) var title: String = "", @ColumnInfo(name = REMINDER_COLUMN_TEXT) var body: String = "", @ColumnInfo(name = REMINDER_COLUMN_TIME) var time: Calendar = Calendar.getInstance(), @ColumnInfo(name = REMINDER_COLUMN_RECURRENCE) var recurrence: Recurrence = Recurrence.NONE, @ColumnInfo(name = REMINDER_COLUMN_EXTERNAL_ID) var externalId: Int = 0, @ColumnInfo(name = REMINDER_COLUMN_NOTIFICATION_ID) var notificationId: Int = 0) { @PrimaryKey @ColumnInfo(name = REMINDER_COLUMN_ID) var id: String = UUID.randomUUID().toString() } Reminder.kt
72. @Entity(tableName = TABLE_REMINDERS) data class Reminder(@ColumnInfo(name = REMINDER_COLUMN_TITLE) var title: String = "", @ColumnInfo(name = REMINDER_COLUMN_TEXT) var body: String = "", @ColumnInfo(name = REMINDER_COLUMN_TIME) var time: Calendar = Calendar.getInstance(), @ColumnInfo(name = REMINDER_COLUMN_RECURRENCE) var recurrence: Recurrence = Recurrence.NONE, @ColumnInfo(name = REMINDER_COLUMN_EXTERNAL_ID) var externalId: Int = 0, @ColumnInfo(name = REMINDER_COLUMN_NOTIFICATION_ID) var notificationId: Int = 0) { @PrimaryKey @ColumnInfo(name = REMINDER_COLUMN_ID) var id: String = UUID.randomUUID().toString() } Reminder.kt
73. @Dao interface ReminderDao { @Insert(onConflict = OnConflictStrategy.REPLACE) fun insertReminder(reminder: Reminder) @Update fun updateReminder(reminder: Reminder) @Delete fun deleteReminder(reminder: Reminder) @Query("SELECT * FROM $TABLE_REMINDERS " + "WHERE $REMINDER_COLUMN_ID = :id") fun getReminderById(id: String): LiveData<Reminder> } ReminderDao.kt
74. How about testing?
75. @RunWith(AndroidJUnit4::class) class ReminderDaoTest { @Before fun createDb() { db = Room.inMemoryDatabaseBuilder(InstrumentationRegistry.getTargetContext(), AppDatabase::class.java) .allowMainThreadQueries() .build() dao = db.reminderDao() } @Test fun testGetReminderById() { val reminder = Reminder(title = TITLE) val id = reminder.id dao.insertReminder(reminder) dao.insertReminder(Reminder()) dao.insertReminder(Reminder()) val result = LiveDataTestUtil.getValue(dao.getReminderById(id)) assertTrue(result.id == id) assertTrue(result.title == TITLE) } ReminderDaoTest.kt
76. @RunWith(AndroidJUnit4::class) class ReminderDaoTest { @Before fun createDb() { db = Room.inMemoryDatabaseBuilder(InstrumentationRegistry.getTargetContext(), AppDatabase::class.java) .allowMainThreadQueries() .build() dao = db.reminderDao() } @Test fun testGetReminderById() { val reminder = Reminder(title = TITLE) val id = reminder.id dao.insertReminder(reminder) dao.insertReminder(Reminder()) dao.insertReminder(Reminder()) val result = LiveDataTestUtil.getValue(dao.getReminderById(id)) assertTrue(result.id == id) assertTrue(result.title == TITLE) } ReminderDaoTest.kt
77. @RunWith(AndroidJUnit4::class) class ReminderDaoTest { @Before fun createDb() { db = Room.inMemoryDatabaseBuilder(InstrumentationRegistry.getTargetContext(), AppDatabase::class.java) .allowMainThreadQueries() .build() dao = db.reminderDao() } @Test fun testGetReminderById() { val reminder = Reminder(title = TITLE) val id = reminder.id dao.insertReminder(reminder) dao.insertReminder(Reminder()) dao.insertReminder(Reminder()) val result = LiveDataTestUtil.getValue(dao.getReminderById(id)) assertTrue(result.id == id) assertTrue(result.title == TITLE) } ReminderDaoTest.kt
78. Pros
79. • No more SQLite APIs Pros
80. • No more SQLite APIs • Easy testing Pros
81. • No more SQLite APIs • Easy testing • Autoupdates with LiveData or RxJava Pros
82. Gotchas
83. • Require Android device/emulator for testing Gotchas
84. • Require Android device/emulator for testing • Room entities require public getters/setters Gotchas
85. • Require Android device/emulator for testing • Room entities require public getters/setters • Handle threading yourself (unless subscribing to LiveData) Gotchas
86. Should I use Room?
87. Should I use Room?
88. LiveData
89. LiveData RxJava2
90. @Dao interface ReminderDao { @Query("SELECT * FROM $TABLE_REMINDERS " + "WHERE $REMINDER_COLUMN_TIME > :time " + "ORDER BY $REMINDER_COLUMN_TIME ASC") fun getAllReminders(time: Long = System.currentTimeMillis()): LiveData<List<Reminder>> } ReminderDao.kt
91. @Dao interface ReminderDao { @Query("SELECT * FROM $TABLE_REMINDERS " + "WHERE $REMINDER_COLUMN_TIME > :time " + "ORDER BY $REMINDER_COLUMN_TIME ASC") fun getAllReminders(time: Long = System.currentTimeMillis()): LiveData<List<Reminder>> } ReminderDao.kt @Dao interface ReminderDao { @Query("SELECT * FROM $TABLE_REMINDERS " + "WHERE $REMINDER_COLUMN_TIME > :time " + "ORDER BY $REMINDER_COLUMN_TIME ASC") fun getAllReminders(time: Long = System.currentTimeMillis()): Flowable<List<Reminder>> }
92. viewModel.reminderList.observe(this, Observer { reminders -> reminders?.let { adapter.setReminderList(it) viewModel.reminderListUpdated(it) fab.show() } }) MainActivity.kt
93. viewModel.reminderList.observe(this, Observer { reminders -> reminders?.let { adapter.setReminderList(it) viewModel.reminderListUpdated(it) fab.show() } }) MainActivity.kt viewModel.reminderList.subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe({ // onNext adapter.setReminderList(it) viewModel.reminderListUpdated(it) fab.show() }, { // onError })
94. fun insertReminder(reminder: Reminder) { Thread(Runnable { dao.insertReminder(reminder) }).start() } ReminderRepo.kt
95. fun insertReminder(reminder: Reminder) { Thread(Runnable { dao.insertReminder(reminder) }).start() } ReminderRepo.kt fun insertReminder(reminder: Reminder): Disposable { return Completable.fromAction { dao.insertReminder(reminder) } .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe() }
96. And of course, testing…
97. @Test fun testGetReminderList() { val time = Calendar.getInstance() time.timeInMillis = System.currentTimeMillis() + 60000 * 5 // set each reminder 5 minutes in future dao.insertReminder(Reminder(time = time)) dao.insertReminder(Reminder(time = time)) val reminders = LiveDataTestUtil.getValue(dao.getAllReminders()) assertTrue(reminders.size == 2) } ReminderDaoTest.kt
98. @Test fun testGetReminderList() { val time = Calendar.getInstance() time.timeInMillis = System.currentTimeMillis() + 60000 * 5 // set each reminder 5 minutes in future dao.insertReminder(Reminder(time = time)) dao.insertReminder(Reminder(time = time)) val reminders = LiveDataTestUtil.getValue(dao.getAllReminders()) assertTrue(reminders.size == 2) } ReminderDaoTest.kt @Test fun testGetReminderList() { val time = Calendar.getInstance() time.timeInMillis = System.currentTimeMillis() + 60000 * 5 // set each reminder 5 minutes in future dao.insertReminder(Reminder(time = time)) dao.insertReminder(Reminder(time = time)) dao.getAllReminders() .test() .assertValue({ it.size == 2 }) }
99. LiveData with RxJava
100. • RxJava for database operations • LiveData for data controlled locally LiveData with RxJava
101. Summary
102. Pros
103. • Lifecycle-aware, officially supported architecture Pros
104. • Lifecycle-aware, officially supported architecture • LiveData autoupdating! Pros
105. • Lifecycle-aware, officially supported architecture • LiveData autoupdating! • Can use individually if desired Pros
106. Gotchas
107. • SingleLiveEvent, LiveDataTestUtil not included Gotchas
108. • SingleLiveEvent, LiveDataTestUtil not included • ViewModelProvider.Factory documentation not great Gotchas
109. • SingleLiveEvent, LiveDataTestUtil not included • ViewModelProvider.Factory documentation not great • Implement threading for Room Gotchas
110. - Google “A collection of libraries that help you design robust, testable, and maintainable apps.”
111. Should I use Architecture Components?
112. Should I use Architecture Components?
113. Want to help? https://github.com/physphil/RemindMe/ Need more info? https://developer.android.com/topic/libraries/architecture/index.html https://github.com/googlesamples/android-architecture-components http://fragmentedpodcast.com/episodes/115/
114. Thanks! Phil Shadlyn @physphil