Architecure components by Paulina Szklarska

ANDROID
ARCHITECTURE
COMPONENTS -
INTRODUCTION
Paulina Szklarska

Hello!
Nice to meet you
Paulina Szklarska
• Android Developer
• co-organizer of Toast Wrocław meetups
• cat owner/travel enthusiast
@pszklarska
@pszklarska
@p_szklarska

1.
INTRO
What are
Architecture
Components?

MVP
MVVM
MVC
VIPER
CLEAN
ARCHITECTURE
MVI
MV-ANYTHING
ARCHITECTURES
?

“
Why there is no official
architecture guide in Android
documentation?
~ me, some time ago

Before
May 2017
https://plus.google.com/+DianneHackborn/posts/FXCCYxepsDU
„Should you use MVC? Or MVP? Or
MVVM? I have no idea. Heck, I only know
about MVC from school and had to do a
Google search to find other options to put
here.”
~ Dianne Hackborn,
Android Framework Engineer,
May 2016

ARCHITECTURE COMPONENTS
ROOM
LIFECYCLE COMPONENTS VIEW MODEL
LIVE DATA PAGING LIBRARY

ROOM
Persistence library for Android

Room Entity
Single database table
DAO
Defines methods to access database
Database
Holds entities and DAOs

Why
another
database
library?
• less boilerplate code (thanks to annotations)
• SQL statement compile-time validation (less
crashes)
• full compatibility with other Architecture
Components (LiveData) and RxJava
• easy to use
• easy to test
• easy to migrate

Cats
id
1
2
3
name
Fudge
Houdini
Scratchy
url
/fudge_photo.jpg
/houdini_photo.jpg
/scratchy_photo.jpg

public class Cat { 
public int id; 
public String name; 
public String url; 
 
public Cat(int id, String name, String url) { 
this.id = id; 
this.name = name; 
this.url = url; 
}a 
}a

@Entity 
public int id; 
 
this.id = id; 
this.url = url; 
}a 
}a

@Entity 
@PrimaryKey 
public int id; 
 
this.id = id; 
this.url = url; 
}a 
}a

@Entity(tableName = „kittens”) 
@PrimaryKey 
public int id; 
 
this.id = id; 
this.url = url; 
}a 
}a

@PrimaryKey(autoGenerate = true) 
public int id; 
 
public Cat(String name, String url) { 
this.url = url; 
}a 
}a

@PrimaryKey(autoGenerate = true) 
public int id; 
public String name;
@ColumnInfo(name = „photo_url”) 
 
public Cat(String name, String url) { 
this.url = url; 
}a 
}a

public interface CatDao { 
 
}a

@Dao 
 
}a

@Dao 
 
@Insert 
void insert(Cat... cats); 
 
@Update 
void update(Cat... cats); 
 
@Delete 
void delete(Cat... cats); 
}a

@Dao 
 
@Query("SELECT * FROM kittens") 
List<Cat> getAllCats(); 
 
@Insert 
 
@Update 
void update(Cat... cats); 
 
@Delete 
void delete(Cat... cats); 
}a

@Dao 
 
@Insert 
 
}a

@Dao 
 
@Insert 
 
@Insert 
void insert(Cat cat); 
 
}a

@Dao 
 
@Insert 
 
@Insert 
 
@Insert 
void insert(List<Cat> catList); 
 
}a

@Dao 
 
@Insert(onConflict = REPLACE) 
 
@Insert(onConflict = IGNORE) 
 
@Insert 
void insert(List<Cat> catList); 
 
}a

@Dao 
 
}a

@Dao 
 
 
@Query("SELECT * FROM kittens WHERE id=:id") 
Cat getCatById(int id); 
 
}a

@Dao 
 
 
 
Cursor getCatsCursor(); 
 
}a

@Dao 
 
 
 
Cursor getCatsCursor(); 
 
@Query("SELECT * FROM kittens WHERE name=:name LIMIT :max") 
List<Cat> getCatsByName(String name, int max); 
 
}a
!UI thread

public class CatDatabase { 
 
}a

@Database(entities = { Cat.class }, version = 1) 
public class CatDatabase { 
 
}a

public abstract class CatDatabase extends RoomDatabase { 
 
}a

 
public abstract CatDao getCatDao(); 
}a

 
private static CatDatabase create(final Context context) { 
return Room.databaseBuilder(
context,
CatDatabase.class,
"catsDatabase.db") 
.build(); 
}
 
 
public abstract CatDao getCatDao(); 
}a

CatDatabase 
.getInstance(context) 
.getCatDao() 
.insert(new Cat(1,  
"Muffin",  
"/muffin.jpg"));
List<Cat> allCats = CatDatabase 
.getInstance(context) 
.getCatDao() 
.getAllCats();

Cats
id
1
2
3
name
Fudge
Houdini
Scratchy
url
/fudge_photo.jpg
/houdini_photo.jpg
/scratchy_photo.jpg
Owner
id
1
2
3
login
John
Cindy
Ken
avatar_url
„/john.jpg”
„/cindy.jpg”
„/ken.jpg”
ownerId
1
1
2

@Entity 
public class Owner { 
@PrimaryKey 
public int id; 
public String login; 
public String avatarUrl; 
 
public Owner(int id, String login, String avatarUrl) { 
this.id = id; 
this.login = login; 
this.avatarUrl = avatarUrl; 
}a 
}a

@Entity 
@PrimaryKey 
public int id; 
public int ownerId; 
 
public Cat(int id, String name, String url, int ownerId) { 
this.id = id; 
this.url = url; 
this.ownerId = ownerId; 
}a 
}a

@Entity(foreignKeys = @ForeignKey(entity = Owner.class)) 
@PrimaryKey 
public int id; 
 
this.id = id; 
this.url = url; 
}a 
}a

@Entity(foreignKeys = @ForeignKey(entity = Owner.class, 
parentColumns = "id")) 
@PrimaryKey 
public int id; 
 
this.id = id; 
this.url = url; 
}a 
}a

parentColumns = "id", 
childColumns = "ownerId")) 
@PrimaryKey 
public int id; 
 
this.id = id; 
this.url = url; 
}a 
}a

parentColumns = "id", 
childColumns = "ownerId", 
onDelete = CASCADE)) 
@PrimaryKey 
public int id; 
 
this.id = id; 
this.url = url; 
}a 
}a

@Dao 
 
@Query("SELECT * FROM kittens WHERE ownerId=:ownerId") 
List<Cat> findCatsForOwner(int ownerId); 
 
}a

public class OwnerWithCats { 
@Embedded public Owner owner; 
 
@Relation(parentColumn = "id", 
entityColumn = "ownerId")
public List<Cat> catList; 
}a

@Dao 
public interface OwnerWithCatsDao { 
 
@Query("SELECT * FROM owner") 
public List<OwnerWithCats> getOwnersWithCats(); 
 
}a

@Entity 
@PrimaryKey 
public int id; 
public LocalDate birthday; 
 
public Cat(int id, String name, LocalDate birthday) { 
this.id = id; 
this.birthday = birthday; 
}a 
}a

public class DateConverter { 
 
@TypeConverter
public LocalDate toDate(long dateLong) {
return LocalDate.ofEpochDay(dateLong);
}
@TypeConverter
public long fromDate(LocalDate date) {
return date.toEpochDay();
} 
}

@TypeConverters(DateConverter.class) 
 
}a

@Entity 
@PrimaryKey public int id; 
}a

@Entity 
@PrimaryKey public int id; 
public String age; 
}a

java.lang.IllegalStateException: Room cannot verify the data
integrity. Looks like you've changed schema but forgot to
update the version number. You can simply fix this by
increasing the version number.

@Database(entities = { Cat.class }, version = 1)a 
return Room 
.databaseBuilder(context, CatDatabase.class, DB_NAME) 
.build();
}a
}a

return Room 
.build();
}a
}a

java.lang.IllegalStateException: A migration from 1 to 2 is necessary.
Please provide a Migration in the builder or call
fallbackToDestructiveMigration in the builder in which case Room will
re-create all of the tables.

return Room 
.build(); 
}a 
}a

return Room 
.databaseBuilder(context, CatDatabase.class, DB_NAME)
.fallbackToDestructiveMigration() 
.build(); 
}a 
}a

return Room 
.addMigrations(Migrations.FROM_1_TO_2) 
.build(); 
}a 
}a

class Migrations { 
static final Migration FROM_1_TO_2 = new Migration(1, 2) { 
@Override 
public void migrate(@NonNull final SupportSQLiteDatabase database) { 
database.execSQL("ALTER TABLE kittens ADD COLUMN age TEXT"); 
} 
}; 
}

android {
javaCompileOptions { 
annotationProcessorOptions { 
arguments = ["room.schemaLocation": 
"$projectDir/schemas".toString()] 
} 
} 
}
}

app/schemas/pl.pszklarska.kittyarchitecture.data.CatDatabase/1.json
"tableName": „kittens", 
"createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (ìd` INTEGER NOT NULL, `name` TEXT,
ùrl` TEXT, PRIMARY KEY(ìd`))", 
"fields": [ 
{ 
"fieldPath": "id", 
"columnName": "id", 
"affinity": "INTEGER", 
"notNull": true 
}, 
{ 
"fieldPath": "name", 
"columnName": "name", 
"affinity": "TEXT", 
"notNull": false 
},
. . .
]

return Room 
.addMigrations(Migrations.FROM_1_TO_2, 
Migrations.FROM_2_TO_3) 
.build(); 
}a 
}a

return Room 
.addMigrations(Migrations.FROM_1_TO_3) 
.build(); 
}a 
}a

@RunWith(AndroidJUnit4.class) 
public class CatEntityTest { 
private CatDao catDao; 
private CatDatabase database; 
 
@Before 
public void createDb() { 
Context context = InstrumentationRegistry.getTargetContext(); 
database = Room.inMemoryDatabaseBuilder(context, CatDatabase.class).build(); 
catDao = database.getCatDao(); 
}a
@After 
public void closeDb() throws IOException { 
database.close(); 
}a 
}a

@RunWith(AndroidJUnit4.class) 
public class CatEntityTest { 
private CatDao catDao; 
private CatDatabase database; 
 
@Before 
public void createDb() { 
Context context = InstrumentationRegistry.getTargetContext(); 
database = Room.inMemoryDatabaseBuilder(context, CatDatabase.class).build(); 
catDao = database.getCatDao(); 
}a 
 
@Test 
public void writeCatAndReadInList() throws Exception { 
Cat cat = new Cat(1, "Jake", „fake_url"); 
catDao.insert(cat); 
List<Cat> catsByName = catDao.getCatsByName(„Jake"); 
assertThat(catsByName.get(0), equalTo(cat)); 
}
@After 
public void closeDb() throws IOException { 
database.close(); 
}a 
}a

tl;dr • less boilerplate code
• SQL statement compile-time validation
• full compatibility with other Architecture
Components and RxJava
• easy to use
• easy to test
• easy to migrate

LIFECYCLE
Lifecycle-aware components

LIFECYCLE
COMPONENTS
LIFECYCLE
OWNER
LIFECYCLE
OBSERVER
- FragmentActivity
- Fragment (support)
- AppCompatActivity

INITIALIZED RESUMEDSTARTEDCREATED
DESTROYED RESUMEDSTARTEDCREATED
ON_CREATE ON_START ON_RESUME
ON_PAUSEON_STOPON_DESTROY

public class MainActivity extends AppCompatActivity implements LocationListener { 
 
private LocationManager locationManager; 
 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_main); 
 
locationManager = new LocationManager(); 
} 
 
@Override 
protected void onStart() { 
super.onStart(); 
locationManager.addLocationListener(); 
} 
 
@Override 
protected void onStop() { 
super.onStop(); 
locationManager.removeLocationListener(); 
} 
 
@Override 
public void onLocationChanged(final Location location) { 
Log.d(„MainActivity", „Location changed: " + location.toString()); 
}

public class LocationManager { 
 
public LocationManager() { 
// do something 
}a 
 
void addLocationListener() { 
// register location manager listener 
}a
 
void removeLocationListener() { 
// remove location manager listener 
}a 
}a

public class LocationManager implements LifecycleObserver { 
 
public LocationManager() {
// do something  
}a 
 
}a 
 
}a 
}a

 
public LocationManager(LifecycleOwner lifecycleOwner) {
// do something  
lifecycleOwner.getLifecycle().addObserver(this); 
}a 
 
}a 
 
}a 
}a

 
// do something  
}a 
 
@OnLifecycleEvent(Lifecycle.Event.ON_START) 
}a 
 
}a 
}a

 
// do something  
}a 
 
@OnLifecycleEvent(Lifecycle.Event.ON_START) 
}a 
 
@OnLifecycleEvent(Lifecycle.Event.ON_STOP) 
}a 
}a

 
 
@Override 
 
locationManager = new LocationManager(); 
}a 
 
@Override 
protected void onStart() { 
super.onStart(); 
locationManager.addLocationListener(); 
} 
 
@Override 
protected void onStop() { 
super.onStop(); 
locationManager.removeLocationListener(); 
} 
 
@Override 
}

 
 
@Override 
 
locationManager = new LocationManager(this); 
}a 
 
@Override 
}a
}a

Lifecycle
Observer
It’s the LocationManager which cares
about the Lifecycle. So it should be able
to do it without the activity
babysitting itself.
I’m sure if you look at your code today,
your onStart(), onStop() methods are
like, at least 20, 30 lines of code. We
want them to be zero lines of code.
~Yigit Boyar, Software Enginner, Google,
Google I/O ‚17

public class GithubApplication extends Application {
@Override
public void onCreate() {
super.onCreate();
ProcessLifecycleOwner.get()
.getLifecycle()
.addObserver(new AppLifecycleObserver());
}
}

public class AppLifecycleObserver implements LifecycleObserver {
@OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
void onFirstActivityCreated() {
// app is in the foreground now
}
@OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
void onLastActivityPaused() {
// app is in the background now
}
}

ACTIVITY
Rotation
ACTIVITY
RECREATED
UI Data
Holder
UI Data
Holder
?
?

ACTIVITY
ACTIVITY
RECREATED
ViewModel
• don’t worry
about UI
data holder
• data will
wait for us
• data will be
always
updated
even after
activity
recreating
Rotation

public class UsersViewModel extends ViewModel { 
 
private List<User> userList; 
 
public List<User> getUserList() { 
if (userList == null) { 
usersList = loadUsers(); 
} 
return userList; 
} 
 
private List<User> loadUsers() { 
// do something to load users 
} 
}

public class UsersViewModel extends AndroidViewModel { 
public UsersViewModel(final Application application) {
super(application);
}
 
 
} 
return userList; 
} 
 
} 
}

public class UsersActivity extends AppCompatActivity { 
 
@Override 
protected void onCreate(final Bundle savedInstanceState) { 
setContentView(R.layout.activity_main);
 
}a 
}a

 
@Override 
 
UsersViewModel usersViewModel = 
ViewModelProviders.of(this).get(UsersViewModel.class); 
 
}a 
}a

 
@Override 
 
 
showUsers(usersViewModel.getUserList()); 
}a 
}a

LiveData<List<User>> observes
notifies
only if activity is
at least started
List<User>

 
 
}a 
return userList; 
}a 
 
}a 
}a

 
private MutableLiveData<List<User>> userList =
new MutableLiveData<>(); 
 
}a 
return userList; 
}a 
 
}a 
}a

 
new MutableLiveData<>(); 
 
public LiveData<List<User>> getUserList() { 
return userList; 
}a 
}a

 
new MutableLiveData<>();
public UsersViewModel() { 
setUserListRefreshCallback(newUserList -> { 
userList.postValue(newUserList); 
}); 
}a 
 
public LiveData<List<User>> getUserList() { 
return userList; 
}a 
}a

 
@Override 
 
 
usersViewModel.getUserList().observe(this, this::showUsers);
 
}a 
}a

tl;dr • keeps your UI always updated (follows
observer pattern)
• no memory leaks (data bound with
lifecycle)
• no data sent to stopped activity

@Dao 
public interface CatDao {
 
@Query("SELECT * FROM cats WHERE name=:name") 
LiveData<List<Cat>> getCatsByName(String name);
 
@Query("SELECT * FROM cats WHERE name=:name") 
Flowable<List<Cat>> getCatsByName(String name);
 
}a

Resources Android Architecture Documentation:
https://developer.android.com/topic/libraries/
architecture/index.html
Guide To App Architecture:
https://developer.android.com/topic/libraries/
architecture/guide.html
Google Samples Repository:
https://github.com/googlesamples/android-
architecture-components
Medium series about Architecture Components:
https://medium.com/@pszklarska

Thanks!
Any questions?
Paulina Szklarska
@pszklarska
@pszklarska
@p_szklarska

Architecure components by Paulina Szklarska

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