A small set of slides showing the usages and introducing the concept of the arch components library

1. Kotlin and Android Arch
Components
Adit Lal
@aditlal

2. Introduction
An application with a solid architecture should be:
•Easy to scale and maintain.
•Each component should be isolated and
decoupled.
•Easy to test
Kotlin and Android Arch Components

3. Kotlin and Android Arch Components

4. Components
Create an UI that
automatically
responds to
lifecycle events.
Lifecycle
Kotlin and Android Arch Components

5. Components
Create an UI that
automatically
responds to
lifecycle events.
Lifecycle LiveData
Build data objects
that notify views
when underlying
data changes
Kotlin and Android Arch Components

6. Components
Create an UI that
automatically
responds to
lifecycle events.
Lifecycle LiveData ViewModel
Build data objects
that notify views
when underlying
data changes
Store UI related
data that isn’t
destroyed on app
rotation
Kotlin and Android Arch Components

7. Components
Create an UI that
automatically
responds to
lifecycle events.
Lifecycle LiveData ViewModel Room
Build data objects
that notify views
when underlying
data changes
Store UI related
data that isn’t
destroyed on app
rotation
Access your data
with the power of
SQLite and safety
of in-app objects.
Kotlin and Android Arch Components

8. Lifecycle
States and Events
Kotlin and Android Arch Components

9. Kotlin and Android Arch Components
Lifecycle

10. Kotlin and Android Arch Components
Lifecycle

11. Kotlin and Android Arch Components

12. Kotlin and Android Arch Components
/**
* Displays a message when app comes to foreground and goes to background.
*/
class AppLifecycleObserver @Inject constructor(context: Context) : LifecycleObserver {
@OnLifecycleEvent(Lifecycle.Event.ON_START)
fun onEnterForeground() {
enterForegroundToast.showAfterCanceling(enterBackgroundToast)
}
@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
fun onEnterBackground() {
enterBackgroundToast.showAfterCanceling(enterForegroundToast)
}
}
Lifecycle

13. Kotlin and Android Arch Components
class AppLifecycleObserver @Inject constructor(context: Context) : LifecycleObserver {
@OnLifecycleEvent(Lifecycle.Event.ON_START)
fun onEnterForeground() {
enterForegroundToast.showAfterCanceling(enterBackgroundToast)
}
@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
fun onEnterBackground() {
enterBackgroundToast.showAfterCanceling(enterForegroundToast)
}
}
Lifecycle
ProcessLifecycleOwner.get().lifecycle.addObserver(appLifecycleObserver)

14. Kotlin and Android Arch Components
/**
* Displays a message when app comes to foreground and goes to background.
*/
class AppLifecycleObserver @Inject constructor(context: Context) : LifecycleObserver {
@OnLifecycleEvent(Lifecycle.Event.ON_START)
fun onEnterForeground() {
enterForegroundToast.showAfterCanceling(enterBackgroundToast)
}
@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
fun onEnterBackground() {
enterBackgroundToast.showAfterCanceling(enterForegroundToast)
}
}
Lifecycle

15. Kotlin and Android Arch Components
/**
* Displays a message when app comes to foreground and goes to background.
*/
class AppLifecycleObserver @Inject constructor(context: Context) : LifecycleObserver {
@OnLifecycleEvent(Lifecycle.Event.ON_START)
fun onEnterForeground() {
enterForegroundToast.showAfterCanceling(enterBackgroundToast)
}
@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
fun onEnterBackground() {
enterBackgroundToast.showAfterCanceling(enterForegroundToast)
}
}
Lifecycle

16. LiveData
LiveData is an observable data holder. It lets the
components in your app, usually the UI, observe
data objects for changes.
Kotlin and Android Arch Components

17. Kotlin and Android Arch Components
LiveData

18. Kotlin and Android Arch Components
LiveData

19. Kotlin and Android Arch Components
LiveData

20. LiveData
var userLiveData : MutableLiveData<List<User>> =
MutableLiveData();

21. LiveData
var userLiveData : MutableLiveData<List<User>> =
MutableLiveData();
userLiveData.value = User(id=1, name="John Doe”)

22. LiveData
var userLiveData : MutableLiveData<List<User>> =
MutableLiveData();
userLiveData.value = User(id=1, name="John Doe”)
//Activity or fragment
viewModel.getUsers().observe(
this,
Observer { result ->
run {
//Handle Result
}
})

23. LiveData

24. ViewModel
Observes the lifecycle state of the view,
maintaining consistency during configuration
changes and other Android lifecycle events.
The ViewModel class is designed to store and
manage UI-related data so that the data survives
configuration changes such as screen rotations.
Kotlin and Android Arch Components

25. ViewModel

26. ViewModel

27. class NoteViewModel
@Inject constructor(var repo: NotesRepository) : ViewModel() {
fun getNotes(sort: String): LiveData<List<Note>> {
return repo.getAllNotes(sort = sort)
}
fun addNote(note: Note): LiveData<Note> {
return repo.addNote(note = note)
}
fun deleteNote(note: Note): LiveData<Int> {
return repo.deleteNote(note)
}
ViewModel

28. class NoteViewModel
@Inject constructor(var repo: NotesRepository) : ViewModel() {
fun getNotes(sort: String): LiveData<List<Note>> {
return repo.getAllNotes(sort = sort)
}
fun addNote(note: Note): LiveData<Note> {
return repo.addNote(note = note)
}
fun deleteNote(note: Note): LiveData<Int> {
return repo.deleteNote(note)
}
ViewModel

29. class NoteViewModel
@Inject constructor(var repo: NotesRepository) : ViewModel() {
fun getNotes(sort: String): LiveData<List<Note>> {
return repo.getAllNotes(sort = sort)
}
fun addNote(note: Note): LiveData<Note> {
return repo.addNote(note = note)
}
fun deleteNote(note: Note): LiveData<Int> {
return repo.deleteNote(note)
}
ViewModel

30. class NotesListActivity : AppCompatActivity(){
private lateinit var notesList: ArrayList<Note>
@Inject lateinit var viewModelFactory: ViewModelFactory
private val viewModel by lazy {
ViewModelProviders.of(
this@NotesListActivity,
viewModelFactory).get(NoteViewModel::class.java)
}
...
}
ViewModel

31. ViewModel

32. @Inject lateinit var viewModelFactory: ViewModelFactory
private val viewModel by lazy { ViewModelProviders.of(this@NotesListActivity,
viewModelFactory).get(NoteViewModel::class.java)
}
//Activity
viewModel.getNotes(sort = sort).observe(
this,
Observer { data ->
run {
notesList.clear()
notesList.addAll(data!!)
adapter.updateItems(notesList)
}
})
ViewModel

33. Room
Persistence library for Android
Kotlin and Android Arch Components

34. Entities and Dao’s
Kotlin and Android Arch Components
Room

35. @Entity(tableName = "user_table")
data class User(var created: Date = Date(),
var name: String = "",
@PrimaryKey var id: Int = 0)
Entities

36. interface BaseDao<T> {
@Insert
fun insert(vararg obj: T)
}
@Dao
abstract class DataDao : BaseDao<Data>() {
@Query("SELECT * FROM Data")
abstract fun getData(): List<Data>
}
Dao

37. @Dao
interface UserDao {
@Insert(onConflict = OnConflictStrategy.REPLACE)
fun insert(user: User)
@Delete
fun delete(user: User)
@Query("SELECT * FROM user_table")
fun getUsers(): List<User>
}
Dao

38. @Dao
interface UserDao {
@Insert(onConflict = OnConflictStrategy.REPLACE)
fun insert(user: User)
@Delete
fun delete(user: User)
@Query("SELECT * FROM user_table")
fun getUsers(): List<User>
}
Dao

39. @Dao
interface UserDao {
@Insert(onConflict = OnConflictStrategy.REPLACE)
fun insert(user: User)
@Delete
fun delete(user: User)
@Query("SELECT * FROM user_table")
fun getUsers(): LiveData<List<User>>
}
Dao

40. @Transaction
open fun updateData(users: List<User>) {
deleteAllUsers()
insertAll(users)
}
Dao

41. class UserAndAllPets {
@Embedded
var user: User? = null
@Relation(parentColumn = “userId”,
entityColumn = “owner”)
var pets: List<Pet> = ArrayList()
}
//UserDao.kt
@Transaction
@Query(“SELECT * FROM Users”)
List<UserAndAllPets> getUsers();
Dao

42. @Database(entities = arrayOf(User::class),
version = 1,
exportSchema = true)
@TypeConverters(Converters::class)
abstract class AppDatabase : RoomDatabase() {
abstract fun UserDao(): UserDao
}
Database

43. class MyApp : Application() {
lateinit var mDataBase: AppDatabase
override fun onCreate() {
super.onCreate()
mDataBase = Room.databaseBuilder(this,
AppDatabase::class.java,
"users").build()
}
}
Database

44. @Provides
@Singleton
fun provideDB(context: Context): AppDatabase =
Room.databaseBuilder(context, AppDatabase::class.java, “users")
.fallbackToDestructiveMigration()
.build()
Database

45. Paging
Efficient Lists and data loading
Kotlin and Android Arch Components

46. Paging

47. Paging

48. class MyPagedListAdapter(diffCallback: DiffCallback<User>) :
PagedListAdapter<User, MyPagedListAdapter.ViewHolder>(diffCallback) {
PagedListAdapter
override fun onBindViewHolder(holder: MyPagedListAdapter.ViewHolder?, position: Int) {
getItem(position)?.let {
holder?.setData(it)
}
}
override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int):
MyPagedListAdapter.ViewHolder {
val view = LayoutInflater.from(parent?.context).inflate(R.layout.item_user, parent, false)
return ViewHolder(view)
}
}

49. class MyPagedListAdapter(diffCallback: DiffCallback<User>) :
PagedListAdapter<User, MyPagedListAdapter.ViewHolder>(diffCallback) {
PagedListAdapter
override fun onBindViewHolder(holder: MyPagedListAdapter.ViewHolder?, position: Int) {
getItem(position)?.let {
holder?.setData(it)
}
}
override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int):
MyPagedListAdapter.ViewHolder {
val view = LayoutInflater.from(parent?.context).inflate(R.layout.item_user, parent, false)
return ViewHolder(view)
}
}

50. class MyPagedListAdapter(diffCallback: DiffCallback<User>) :
PagedListAdapter<User, MyPagedListAdapter.ViewHolder>(diffCallback) {
PagedListAdapter
override fun onBindViewHolder(holder: MyPagedListAdapter.ViewHolder?, position: Int) {
getItem(position)?.let {
holder?.setData(it)
}
}
override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int):
MyPagedListAdapter.ViewHolder {
val view = LayoutInflater.from(parent?.context).inflate(R.layout.item_user, parent, false)
return ViewHolder(view)
}
}

51. DiffCallback
private val diffCallback = object : DiffUtil.ItemCallback<User>() {
override fun areItemsTheSame(oldItem: User, newItem: User): Boolean =
oldItem.id == newItem.id
override fun areContentsTheSame(oldItem: User, newItem: User): Boolean =
oldItem == newItem
}
}

52. Query
@Query("SELECT * FROM users ORDER WHERE age>:age ORDER by
name DESC, id ASC")
abstract fun usersOlderThan(age: Int): LivePagedListProvider<Int, User>

53. ViewModel
class UserViewModel(val db:AppDB) : ViewModel() {
val users: LiveData<PagedList<User>>
fun getUsersOlderThan(age) {
users = db.userDao().usersOlderThan(age)
.create(0, PagedList.Config.Builder()
.setPageSize(20)
.setPrefetchDistance(20)
.setEnablePlaceholders(false)
.build())
}
}

54. Activity
viewModel.getUsersOlderThan(5).observe(this, pagedList -> {
usersAdapter.setList(pagedList);
});

55. Thank you
Questions
Kotlin and Android Arch Components
@aditlal