Android Architecture Components - Guy Bar on, Vonage

Android Architecture
Components
Guy Baron, Director Mobile @ Vonage
DroidCon TLV 2017

Backend SQLite DB UI Users
Retrofit Boilerplate!
Lifecycle?
MVP ?
MVVM ?

Android Architecture Components
Make it easier and more fun to write robust apps, empowering developers to focus
on areas where they can innovate.
Issues like complex lifecycles and the lack of a recommended app architecture
make it challenging to write robust apps.

https://developer.android.com/topic/libraries/architecture/guide.html

App Architecture Concepts
Abstraction layer over SQLite
● Room - light ORM library
● Allows fluent database access
Repository
● Responsible for handling data
operations.
● Knows where to get the data from and
what API calls to make when data is
updated

Room
@Entity
class User {
private @PrimaryKey int uid;
private @ColumnInfo(name = "first_name") String firstName;
}
@Dao
interface UserDao {
@Query("SELECT * FROM user ORDER BY first_name ASC")
public abstract List<User> usersByLastName();
}
@Database(entities = {User.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {
public abstract UserDao userDao();
}

LiveData
● LiveData is an observable lifecycle-
aware data holder class

Room & LiveData
@Entity
class User {
}
@Dao
interface UserDao {
public abstract LiveData<List<User>> usersByLastName();
}
}

ViewModel
● Stores UI-related data in a lifecycle
conscious way
Lifecycle-aware components
● LifecycleOwner / LifecycleObserver

Room & LiveData & ViewModel
@Entity
class User {
}
@Dao
interface UserDao {
}
}
class MyViewModel extends ViewModel {
public final LiveData<List<User>> usersList;
public MyViewModel() {
AppDatabase db = Room.databaseBuilder(context,
AppDatabase.class, "database-name").build();
usersList = db.userDao().usersByLastName();
}
}

Room & LiveData & ViewModel & UI
@Entity
class User {
}
@Dao
interface UserDao {
}
}
public final LiveData<List<User>> usersList;
}
}
class MyActivity extends AppCompatActivity {
@Override
public void onCreate(Bundle savedState) {
super.onCreate(savedState);
MyViewModel viewModel = ViewModelProviders.of(this)
.get(MyViewModel.class);
// ...
}
}

Data Flow
Room
Use Room to store the new data
in the SQLite database for
offline use
ViewModel
Store the data in a ViewModel
object to make it accessible for
UI objects
BE Service
Use the Retrofit library to
access your backend and fetch
for data
LiveData
Use Room to fetch data from
the SQLite database and get
LiveData objects
UI
Activities access the data using
the ViewModel. They observe
and respond to changes

Backend SQLite DB UI Users
Retrofit Room
Lifecycle
LiveData
ViewModel

Why paging is interesting
● We use SQLiteCursor for fetching data from the database
● SQLiteCursor uses a CursorWindow, a buffer of rows typically 2MB in size
● Challenges:
○ SQLiteCursor doesn’t hold any database transaction open
○ SQLiteCursor.getCount() scans entire query
○ SQLiteCursor does not know data has changed

SQLiteCursor doesn’t hold any database transaction open
cursor.moveToPosition(position);

SQLiteCursor doesn’t hold any database transaction open
cursor.moveToNext();

SQLiteCursor.getCount() scans entire query
cursor.getCount();

The Paging library
● Uses small queries
● Queries that fit within a single CursorWindow

Room & LiveData & ViewModel & UI & Paging
@Entity
class User {
}
@Dao
interface UserDao {
}
}

@Entity
class User {
}
@Dao
interface UserDao {
public abstract DataSource.Factory<Integer, User> usersByLastName();
}
}

@Entity
class User {
}
@Dao
interface UserDao {
}
}
LiveData<List<User>> usersList;
}
}

@Entity
class User {
}
@Dao
interface UserDao {
}
}
LiveData<PagedList<User>> usersList;
usersList = new LivePagedListBuilder<>(
db.userDao.usersByLastName(),20).build();
}
}

@Entity
class User {
}
@Dao
interface UserDao {
}
}
LiveData<PagedList<User>> usersList;
usersList = new LivePagedListBuilder<>(
db.userDao.usersByLastName(),20).build();
}
}
class MyActivity extends AppCompatActivity {
public void onCreate(Bundle savedState) {
super.onCreate(savedState);
MyViewModel viewModel = ViewModelProviders.of(this).
get(MyViewModel.class);
viewModel.usersList.observe(this, new Observer<PagedList<User>>() {
void onChanged(PagedList<User> users) {
adapter.setList(users);
}
});
}

Android Architecture Components - Guy Bar on, Vonage

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