Android
Componentes de la arquitectura de Android

Introducción

Añadir componentes de arquitectura

Proyecto build.gradle

allprojects {
    repositories {
        jcenter()
        // Add this if you use Gradle 4.0+
        google()
        // Add this if you use Gradle < 4.0
        maven { url 'https://maven.google.com' }
    }
}

ext {
    archVersion = '1.0.0-alpha5'
}

Aplicación para construir Gradle

// For Lifecycles, LiveData, and ViewModel
compile "android.arch.lifecycle:runtime:$archVersion"
compile "android.arch.lifecycle:extensions:$archVersion"
annotationProcessor "android.arch.lifecycle:compiler:$archVersion"

// For Room
compile "android.arch.persistence.room:runtime:$archVersion"
annotationProcessor "android.arch.persistence.room:compiler:$archVersion"

// For testing Room migrations
testCompile "android.arch.persistence.room:testing:$archVersion"

// For Room RxJava support
compile "android.arch.persistence.room:rxjava2:$archVersion"

Usando Lifecycle en AppCompatActivity

Extiende tu actividad de esta actividad

public abstract class BaseCompatLifecycleActivity extends AppCompatActivity implements LifecycleRegistryOwner {
    // We need this class, because LifecycleActivity extends FragmentActivity not AppCompatActivity

    @NonNull
    private final LifecycleRegistry lifecycleRegistry = new LifecycleRegistry(this);

    @NonNull
    @Override
    public LifecycleRegistry getLifecycle() {
        return lifecycleRegistry;
    }
}

ViewModel con transformaciones de LiveData

public class BaseViewModel extends ViewModel {
    private static final int TAG_SEGMENT_INDEX = 2;
    private static final int VIDEOS_LIMIT = 100;

    // We save input params here
    private final MutableLiveData<Pair<String, String>> urlWithReferrerLiveData = new MutableLiveData<>();

    // transform specific uri param to "tag"
    private final LiveData<String> currentTagLiveData = Transformations.map(urlWithReferrerLiveData, pair -> {
        Uri uri = Uri.parse(pair.first);
        List<String> segments = uri.getPathSegments();
        if (segments.size() > TAG_SEGMENT_INDEX)
            return segments.get(TAG_SEGMENT_INDEX);
        return null;
    });

    // transform "tag" to videos list
    private final LiveData<List<VideoItem>> videoByTagData = Transformations.switchMap(currentTagLiveData, tag -> contentRepository.getVideoByTag(tag, VIDEOS_LIMIT));

    ContentRepository contentRepository;

    public BaseViewModel() {
        // some inits
    }

    public void setUrlWithReferrer(String url, String referrer) {
        // set value activates observers and transformations
        urlWithReferrerLiveData.setValue(new Pair<>(url, referrer));
    }

    public LiveData<List<VideoItem>> getVideoByTagData() {
        return videoByTagData;
    }
}

En algún lugar de la interfaz de usuario:

public class VideoActivity extends BaseCompatLifecycleActivity {
    private VideoViewModel viewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Get ViewModel
        viewModel = ViewModelProviders.of(this).get(BaseViewModel.class);
        // Add observer
        viewModel.getVideoByTagData().observe(this, data -> {
            // some checks
            adapter.updateData(data);
        });

        ...
        if (savedInstanceState == null) {
            // init loading only at first creation
            // you just set params and 
            viewModel.setUrlWithReferrer(url, referrer);
        }
}

Habitación peristence

La sala requiere cuatro partes: clase de base de datos, clases DAO, clases de entidad y clases de migración (ahora puede usar solo métodos DDL ):

Clases de entidad

// Set custom table name, add indexes
@Entity(tableName = "videos",
        indices = {@Index("title")}
)
public final class VideoItem {
    @PrimaryKey // required
    public long articleId;
    public String title;
    public String url;
}

// Use ForeignKey for setup table relation
@Entity(tableName = "tags",
        indices = {@Index("score"), @Index("videoId"), @Index("value")},
        foreignKeys = @ForeignKey(entity = VideoItem.class,
                parentColumns = "articleId",
                childColumns = "videoId",
                onDelete = ForeignKey.CASCADE)
)
public final class VideoTag {
    @PrimaryKey
    public long id;
    public long videoId;
    public String displayName;
    public String value;
    public double score;
}

Clases de dao

@Dao
public interface VideoDao {
    // Create insert with custom conflict strategy
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void saveVideos(List<VideoItem> videos);

    // Simple update
    @Update
    void updateVideos(VideoItem... videos);

    @Query("DELETE FROM tags WHERE videoId = :videoId")
    void deleteTagsByVideoId(long videoId);

    // Custom query, you may use select/delete here
    @Query("SELECT v.* FROM tags t LEFT JOIN videos v ON v.articleId = t.videoId WHERE t.value = :tag ORDER BY updatedAt DESC LIMIT :limit")
    LiveData<List<VideoItem>> getVideosByTag(String tag, int limit);
}

Clase de base de datos

// register your entities and DAOs
@Database(entities = {VideoItem.class, VideoTag.class}, version = 2)
public abstract class ContentDatabase extends RoomDatabase {
    public abstract VideoDao videoDao();
}

Migraciones

public final class Migrations {
    private static final Migration MIGRATION_1_2 = new Migration(1, 2) {
        @Override
        public void migrate(SupportSQLiteDatabase database) {
            final String[] sqlQueries = {
                    "CREATE TABLE IF NOT EXISTS `tags` (`id` INTEGER PRIMARY KEY AUTOINCREMENT," +
                            " `videoId` INTEGER, `displayName` TEXT, `value` TEXT, `score` REAL," +
                            " FOREIGN KEY(`videoId`) REFERENCES `videos`(`articleId`)" +
                            " ON UPDATE NO ACTION ON DELETE CASCADE )",
                    "CREATE  INDEX `index_tags_score` ON `tags` (`score`)",
                    "CREATE  INDEX `index_tags_videoId` ON `tags` (`videoId`)"};
            for (String query : sqlQueries) {
                database.execSQL(query);
            }
        }
    };

    public static final Migration[] ALL = {MIGRATION_1_2};

    private Migrations() {
    }
}

Usar en la clase de aplicación o proporcionar a través de Dagger

ContentDatabase provideContentDatabase() {
    return Room.databaseBuilder(context, ContentDatabase.class, "data.db")
            .addMigrations(Migrations.ALL).build();
}

Escribe tu repositorio:

public final class ContentRepository {
    private final ContentDatabase db;
    private final VideoDao videoDao;

    public ContentRepository(ContentDatabase contentDatabase, VideoDao videoDao) {
        this.db = contentDatabase;
        this.videoDao = videoDao;
    }

    public LiveData<List<VideoItem>> getVideoByTag(@Nullable String tag, int limit) {
        // you may fetch from network, save to database
        ....
        return videoDao.getVideosByTag(tag, limit);
    }
}

Usar en ViewModel:

ContentRepository contentRepository = ...;
contentRepository.getVideoByTag(tag, limit);

LiveData personalizado

Puede escribir LiveData personalizado, si necesita lógica personalizada.
No escriba una clase personalizada, si solo necesita transformar datos (use la clase Transformaciones)

public class LocationLiveData extends LiveData<Location> {
    private LocationManager locationManager;
    
    private LocationListener listener = new LocationListener() {
        @Override
        public void onLocationChanged(Location location) {
            setValue(location);
        }

        @Override
        public void onStatusChanged(String provider, int status, Bundle extras) {
            // Do something
        }

        @Override
        public void onProviderEnabled(String provider) {
            // Do something
        }

        @Override
        public void onProviderDisabled(String provider) {
            // Do something
        }
    };

    public LocationLiveData(Context context) {
        locationManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
    }

    @Override
    protected void onActive() {
        // We have observers, start working
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, listener);
    }

    @Override
    protected void onInactive() {
        // We have no observers, stop working
        locationManager.removeUpdates(listener);
    }
}

Componente personalizado de ciclo de vida

Cada ciclo de vida del componente UI cambió como se muestra en la imagen. Puede crear un componente, que se notificará en el cambio de estado del ciclo de vida:

public class MyLocationListener implements LifecycleObserver {
    private boolean enabled = false;
    private Lifecycle lifecycle;
    public MyLocationListener(Context context, Lifecycle lifecycle, Callback callback) {
       ...
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    void start() {
        if (enabled) {
           // connect
        }
    }

    public void enable() {
        enabled = true;
        if (lifecycle.getState().isAtLeast(STARTED)) {
            // connect if not connected
        }
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    void stop() {
        // disconnect if connected
    }
}