[App devcon 18] Brace yourself with Android Architecture Components

AppDevCon 2018
Michelantonio Trizio
@mik3lantoni0

Mike Trizio - @mik3lantoni0 - #nerdipity
Michelantonio Trizio
GDG Bari community lead
Computer Science Engineer
Android Dev
CTO @ Wideverse

SPOILER ALERT

About architecture components
➔ Announced at Google I/O 2017 and became stable last november
➔ Provide frameworks to create more maintainable and robust app
➔ Foster components decoupling within the app

What’s the problem?

The solution
Follow architectural principle
➔ Separation of concerns
➔ Drive your UI from a model (preferably persistent one)

App architecture

SEASON 1
1x01 - Room
1x02 - Lifecycle
1x03 - ViewModel
1x04 - LiveData
1x05 - Paging

1x01 - Room

Data layer before Room

Room architecture diagram

Components of room
@Entity: annotation needed define a table
@Dao: annotation needed define a Data Access Object
@Database: annotation to create the database holder

Create an entity
@Entity(tableName = "characters")
class Character {
@PrimaryKey (autoGenerate = true)
public int id;
public String firstName;
@NonNull
public String lastName;
@Ignore
Bitmap picture;
}
character table
id (PK) firstName LastName
1 Walter White
2 Jesse Pinkman
3 Gustavo Fring

Create a Dao
Annotations available
@Dao
@Insert
@Delete
@Update
@Query
@Dao
public interface CharacterDao {
@Query("SELECT * FROM characters")
List<User> getAll();
@Insert
void insertAll(Character... characters);
@Delete
void delete(Character character);
}

Create the Database
@Database(entities = {Character.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {
private static AppDatabase sInstance;
public abstract CharacterDao characterDao(); //Getters for Dao
public static AppDatabase getInstance(Context context) {
if (sInstance == null)
sInstance = Room.databaseBuilder(getApplicationContext(),
AppDatabase.class, "database-name").build();
return sInstance;
}
}

get and use Database instance
//GET DATABASE INSTANCE
AppDatabase database = AppDatabase.getInstance(Context context);
//GET ALL CHARACTERS INTO THE DB
List<Character> allCharacters = database.characterDao().getAll();

Query example
@Query("SELECT * FROM characters WHERE first_name LIKE :first AND last_name
LIKE :last LIMIT 1")
Character findByName(String first, String last);

Transaction
@Dao
public abstract class CharacterDao {
@Transaction
public void updateCharacters(List<Characters> characterList) {
deleteAllCharacter()
insertAll(characterList)
}
@Insert
public insertAll(users: List<User>);
@Query("DELETE FROM Users")
public void deleteAllUsers();
}

Migration (1)
@Database(entities = {Character.class}, version = 2) //update the version
public abstract class AppDatabase extends RoomDatabase {
private static SunshineDatabase sInstance;
public abstract CharacterDao characterDao();
public static AppDatabase getInstance(Context context) {
...
}
}

Migration (2)
@Entity(tableName = "characters")
class Character {
public int id;
public String firstName;
public String lastName;
public String alias; //add the alias field
@Ignore
public Bitmap picture;
}

Migration (3)
Room.databaseBuilder(getApplicationContext(), MyDb.class,
"database-name").addMigrations(MIGRATION_1_2).build();
static final Migration MIGRATION_1_2 = new Migration(1, 2) {
@Override
public void migrate(SupportSQLiteDatabase database) {
database.execSQL("ALTER TABLE character add column alias text");
}
}

Ask only what you need (1)
public class SimpleSeries {
public int id;
public String title;
}
@Entity(tableName = "series")
public class Series {
public int id;
public String title;
public String description;
}

Ask only what you need (2)
@Query("SELECT series.id, series.title FROM series")
List<SimpleSeries> getSimpleSeries();

@Relation and one to many query
public class SeriesAndAllCharacters {
@Embedded
private Series series;
@Relation(parentColumn = “id”,
entityColumn = “seriesId”)
private List<Character> characters;
}

@Relation and the Dao
@Transaction
@Query(“SELECT * FROM Series”)
List<SeriesAndAllCharacters> getSeries();

Libraries comparison
➔ Realm is the most robust
➔ ObjectBox is fastest
➔ Room is lightest

1x02 - Lifecycle

Android activity lifecycle

going upside down... or simply rotate the phone

...a lot of stranger things can happen

public class MyObserver implements LifecycleObserver {
@OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
public void onResume() {
}
@OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
public void onPause() {
}
}
aLifecycleOwner.getLifecycle().addObserver(new MyObserver());
Lifecycle observer implementation

observable events
ON_CREATE ON_DESTROY ON_PAUSE
ON_RESUME ON_START ON_STOP

LifecycleOwner
public class MyActivity extends LifecycleActivity {
private MyObeserver myObeserver;
public void onCreate(...) {
myObeserver = new MyObeserver(this, location ->{
// update UI
});
}
since Support Library 26.1.0 AppCompatActivity and Support Fragments implements
LifecycleOwner before that we need to use LifecycleActivity

1x03 - ViewModel

ViewModels persist configuration change

Interaction of entities in an app built with
Architecture components

public class CharacterDetailViewModel extends ViewModel {
private Character mCharacter;
public CharacterDetailViewModel(CharacterDao dao, int characterId) {
mCharacter = dao.getDetails(id);
}
public Character getCharacter(){
return mCharacter;
}
}
Create a viewModel (1)

Create a viewModel - in the Activity(2)
private CharacterDetailViewModel characterViewModel;
protected void onCreate(Bundle savedInstanceState){
CharacterModelFactory characterFactory =
new CharacterModelFactory(dao, characterId);
characterViewModel =
ViewModelProviders.of(this, characterModelFacotry)
.get(CharacterDetailViewModel.class)
}
}

1x04 - LiveData

DING DING DING!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

LiveData example
MutableLiveData<String> name =
new MutableLiveData<String>();
name.setValue("Saul");
name.observe(<LIFECYCLE OWNER>,
newName -> {
// Do something when the observer
is triggered; usually updating the
UI
});

merge liveData and viewModel
public CharacterDetailViewModel(){
mCharacter = new
MutableLiveData<>();
}
mViewModel.getCharacter().observe(
this, characterEntry -> {
// Update the UI
});
if (characterEntry != null)
bindWeatherToUI(characterEntry);

Add a new character live

Avoid false positive for observable queries
@Query(“SELECT * FROM Users WHERE characterId = :id”)
LiveData<Character> getCharacterById(long id)
➔ DELETE, UPDATE or INSERT operations on a table generate a trigger
➔ Room creates an InvalidationTracker
➔ LiveData receives the InvalidationTracker and it triggers a re-query

Filtering emissions (1)
final MediatorLiveData distinctLiveData = new MediatorLiveData<>();
distinctLiveData.addSource(simpleUserLiveData, new Observer<SimpleUser>() {
...
});

Filtering emissions (2)
private SimpleSeries lastSimpleSeries = null;
@Override
public void onChanged(@Nullable SimpleSeries changedSimpleSeries) {
if(lastSimpleSeries == null){
lastSimpleSeries = changedSimpleSeries;
distinctLiveData.postValue(lastSimpleSeries);
}else if((changedSimpleSeries != null && lastSimpleSeries != null)
|| !lastSimpleSeries.equals(changedSimpleSeries)){
lastSimpleSeries = changedSimpleSeries;
distinctLiveData.postValue(lastSimpleSeries);
}
}
}

1x05 - Paging

when we deal with a lot of data….

➔ It’s easier to gradually load
information as needed from a data
source
➔ No overloading the device or
waiting too long for a big database
query
➔ The workflow is mainly in the
background
Only a trailer...

Recap
1. Room - provide simple interaction with database
2. Lifecycle - better dealing with Activity Lifecycle
3. ViewModel - way to hold and manage data
4. LiveData - data holder lifecycle aware that allow to observe data
5. Paging - easy and light way to load information as needed

what’s next?
Architecture components guide
https://goo.gl/j5Zztk
Architecture talk @ GDD Krakow 2017
https://goo.gl/6C2fvr
Architecture guide codelab
https://goo.gl/gF9Vyu

That’s all folks!!!

Questions?

Thank you!
Rate this talk please
https://goo.gl/TDT5Hb
Follow me
@mik3lantoni0

[App devcon 18] Brace yourself with Android Architecture Components

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