Introduction to Android Architecture Components

Android OS was released more than ten years, and a lot of best practices were published and promoted.

As Android developers, we face many challenges like handling life-cycle events, persisting data, maintaining view state, etc. Our constant struggle for a good architecture was not left unnoticed, Google stepped up and gave us their own take on the topic in the form of Architecture Components.

During this talk, we will explore how API of LiveData, ViewModel, Lifecycle and Room libraries.

Transcript

1. Introduction to Android
   Architecture Components
   @Alex_Zhukovich
   alexzh.com
   Andrzej Jóźwiak
   ajoz.github.io
   

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2. Android JetPack
   

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3. https://android-developers.googleblog.com/2018/05/use-android-jetpack-to-accelerate-your.html
   

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4. Support
   Libraries
   AndroidX
   

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5. https://github.com/foobaz42/CompanyContacts
   

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6. Activity ViewModel Repository
   Local data
   source
   Remote data
   source
   

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7. ViewModel
   Lifecycle
   LiveData Room
   

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8. Lifecycle
   

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9. public class TestFragment extends Fragment{
   @Override
   void onStart() {
   registerComponent1(...);
   registerComponent2(...);
   registerComponent3(...);
   }
   @Override
   void onStop() {
   unregisterComponent1(...);
   unregisterComponent2(...);
   unregisterComponent3(...);
   }
   }
   

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10. public class TestActivity
    extends AppCompatActivity {
    private Component component1;
    @Override
    void onCreate(Bundle bundle) {
    Component1 = new Component(
    this // Lifecycle object
    )
    }
    ...
    }
    public class Component1
    implements LifecycleObserver {
    public Component1(Lifecycle lifecycle) {
    lifecycle.addObserver(this)
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    void start() {
    ...
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    void stop() {
    ...
    }
    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    void destroy() {
    lifecycle.removeObserver(this)
    }
    }
    

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11. Lifecycle
    Lifecycle
    Observer
    Lifecycle
    Owner
    Lifecycle
    Registry
    

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12. public abstract class Lifecycle {
    public enum State {
    DESTROYED,
    INITIALIZED,
    CREATED,
    STARTED,
    RESUMED;
    }
    public enum Event {
    ON_CREATE,
    ON_START,
    ON_RESUME,
    ON_PAUSE,
    ON_STOP,
    ON_DESTROY,
    ON_ANY
    }
    }
    

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13. Fragment
    AppCompatActivity
    LifecycleService
    

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14. 700 ms
    

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15. ViewModel
    

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16. View
    Business
    Logic
    Data
    Repository
    UI Events
    Data
    Change
    Events
    Create
    Update
    Delete
    Read
    

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17. View ViewModel Model
    UI Events
    Property
    Change
    Events
    Create
    Update
    Delete
    Read
    ViewModel
    data
    Model
    Change
    Events
    

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18. ?
    custom Application with static fields
    or stopping any configuration changes
    in the AndroidManifest.xml
    onSaveInstanceState(Bundle)
    onCreate(Bundle)
    Object onRetainNonConfigurationInstance()
    Object getLastNonConfigurationInstance()
    retaining a Fragment with
    setRetainInstance(true)
    

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19. large amounts
    of business
    related data
    data that takes
    long to load
    data that takes
    long to process
    partial data that
    is still loading
    data that is
    hard to
    serialize
    data that is
    NOT related to
    View
    data that is NOT
    related to the
    Activity context
    data that is NOT
    Lifecycle
    reference
    ViewModel
    

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20. class TeamsViewModel(): ViewModel() {
    fun someDomainRelatedMethod() {
    // very very very import stuff ...
    }
    }
    

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21. class TeamsActivity : AppCompatActivity(){
    // It is not necessary to hold this reference
    private lateinit var viewModel: TeamsViewModel
    override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    viewModel = ViewModelProviders.of(this)
    .get(TeamsViewModel::class.java)
    // we can use it now or later ...
    viewModel.someDomainRelatedMethod()
    }
    }
    

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22. LiveData
    

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23. data holder
    observed within a
    lifecycle
    Observer paired
    with
    LifecycleOwner
    this is NOT a
    Stream
    this is NOT an Rx
    Observable
    this is NOT a
    Sequence
    LiveData
    MutableLiveData
    MediatorLiveData
    

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24. LiveData + ViewModel
    

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25. class TeamsViewModel(): ViewModel() {
    private val teams: MutableLiveData> by lazy {
    MutableLiveData().also {
    loadTeams()
    }
    }
    fun loadTeams() {
    // Async operations to load data
    // from database/cache/cloud
    teams.value = // values
    }
    fun getTeams(): LiveData> {
    return teams
    }
    }
    

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26. class TeamsActivity : AppCompatActivity(){
    private lateinit var viewModel: TeamsViewModel
    override fun onCreate(savedInstanceState: Bundle?) {
    // ...
    viewModel = ViewModelProviders.of(this)
    .get(TeamsViewModel::class.java)
    viewModel.getTeams().observe(
    this,
    Observer>{ teams ->
    // update UI with the acquired data
    }
    )
    }
    }
    

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27. class TeamsViewModel(apl: Application): AndroidViewModel(apl) {
    fun someDomainRelatedMethod() {
    // Application instance is available through
    // - getApplication() method in Java
    // - application property in Kotlin
    }
    }
    

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28. class TeamsViewModel(
    private val teamRepository: TeamRepository
    ): ViewModel() {
    fun fetchTeams(): LiveData> {
    // accessing the injected dependency
    return teamRepository.fetchTeams()
    }
    }
    

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29. class TeamsFactory(
    private val repository: TeamRepository
    ) : ViewModelProvider.Factory {
    override fun create( modelClass: Class): TeamsViewModel {
    if (modelClass.isAssignableFrom( TeamsViewModel::class.java)) {
    return TeamsViewModel(repository)
    }
    throw IllegalArgumentException(“Unknown model class!”)
    }
    }
    

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30. class TeamsActivity : AppCompatActivity(){
    private lateinit var viewModel: TeamsViewModel
    override fun onCreate(savedInstanceState: Bundle?) {
    val repository = //injecting the dependency
    viewModel = ViewModelProviders
    // ViewModelProvider.Factory has to be specified
    // manually
    .of(this, TeamsFactory(repository))
    .get(TeamsViewModel::class.java)
    }
    }
    

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31. MediatorLiveData
    X X X X
    Y Y Y Y
    values returned by the
    “Mediator”
    func: X -> Y
    source:
    LiveData
    func: X -> Y
    Transformations.map(source, func)
    values returned by the “Source”
    

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32. ViewModel LiveData
    NOT well suited for
    single Events
    by default models
    ONLY happy path
    there is NO error
    “channel”
    NO API contract for
    error handling
    NO way to
    determine the
    amount of results
    LIMITED amount of
    operators
    

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33. Room
    

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35. API 1 API 8 API 21 API 26 API 28
    API 3 API 11 API 24 API 27
    SQLite 3.4
    SQLite 3.5
    SQLite 3.6
    SQLite 3.7
    SQLite 3.8
    SQLite 3.9
    SQLite 3.18
    SQLite 3.19
    SQLite 3.22
    

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36. val db = dbHelper.readableDatabase
    // Define a projection that specifies which columns from the database
    // you will actually use after this query.
    val projection = arrayOf(BaseColumns._ID,
    FeedEntry.COLUMN_NAME_TITLE,
    FeedEntry.COLUMN_NAME_SUBTITLE)
    // Filter results WHERE "title" = 'My Title'
    val selection = "${FeedEntry.COLUMN_NAME_TITLE} = ?"
    val selectionArgs = arrayOf("My Title")
    // How you want the results sorted in the resulting Cursor
    val sortOrder = "${FeedEntry.COLUMN_NAME_SUBTITLE} DESC"
    val cursor = db.query(
    FeedEntry.TABLE_NAME, // The table to query
    projection, // The array of columns to return (pass null to get all)
    selection, // The columns for the WHERE clause
    selectionArgs, // The values for the WHERE clause
    null, // don't group the rows
    null, // don't filter by row groups
    sortOrder // The sort order
    )
    

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37. val db = dbHelper.readableDatabase
    // Define a projection that specifies which columns from the database
    // you will actually use after this query.
    val projection = arrayOf(BaseColumns._ID,
    FeedEntry.COLUMN_NAME_TITLE,
    FeedEntry.COLUMN_NAME_SUBTITLE)
    // Filter results WHERE "title" = 'My Title'
    val selection = "${FeedEntry.COLUMN_NAME_TITLE} = ?"
    val selectionArgs = arrayOf("My Title")
    // How you want the results sorted in the resulting Cursor
    val sortOrder = "${FeedEntry.COLUMN_NAME_SUBTITLE} DESC"
    val cursor = db.query(
    FeedEntry.TABLE_NAME, // The table to query
    projection, // The array of columns to return (pass null to get all)
    selection, // The columns for the WHERE clause
    selectionArgs, // The values for the WHERE clause
    null, // don't group the rows
    null, // don't filter by row groups
    sortOrder // The sort order
    )
    SELECT id, title, subTitle FROM Feed WHERE title = ? ORDER BY subTitle DESC
    

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38. SELECT * FROM employees WHERE team_id = :teamId
    

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39. @Dao
    interface EmployeeDao {
    @Query("SELECT * FROM employees WHERE team_id = :teamId")
    fun getEmployeesByTeamId(): List
    }
    

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40. @Insert
    fun insert(employee: Employee): Long
    @Insert
    fun insertListOfEmployees(employees: List)
    @Insert
    fun insertEmployees(vararg employee: Employee): List
    

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41. @Update
    fun updateEmployee(employee: Employee): Int
    @Update
    fun updateEmployees(employees: List): Int
    @Update
    fun updateEmployee(employee: Employee)
    

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42. @Delete
    fun deleteEmployee(employee: Employee): Int
    @Delete
    fun deleteEmployee(employees: List)
    @Delete
    fun deleteEmployee(vararg employee: Employee): Int
    

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43. @Dao
    interface EmployeesDAO {
    @Query("SELECT * FROM employees WHERE team_id = :teamId")
    fun getEmployeesByTeamId(teamId: Long): LiveData>
    @Insert(onConflict = OnConflictStrategy.
    REPLACE)
    fun insertEmployee(employee: Employee)
    @Update
    fun updateEmployee(employee: Employee): Int
    @Delete
    fun deleteEmployee(employee: Employee): Int
    }
    

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44. @Entity
    data class Employee(
    @PrimaryKey val id: Long,
    val name: String,
    val phone: String)
    

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45. @Entity(tableName = "employees")
    data class Employee(
    @PrimaryKey @ColumnInfo(name = "employee_id") val id: Long,
    @ColumnInfo(name = "employee_name") val name: String,
    @ColumnInfo(name = "employee_phone") val phone: String)
    

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46. @Database(entities = [Team::class, Employee::class], version = 1)
    abstract class ContactsDatabase: RoomDatabase() {
    abstract fun teamsDao(): TeamsDAO
    abstract fun employeesDao(): EmployeesDAO
    }
    

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47. @Alex_Zhukovich
    alexzh.com
    Andrzej Jóźwiak
    ajoz.github.io
    

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