The document discusses Android Architecture Components which provide lifecycle-aware observables, lightweight ViewModels, and object mapping for SQLite. It describes lifecycles and how they allow observers to automatically subscribe and unsubscribe from data based on a component's lifecycle state. LiveData is introduced as an observable data holder that is lifecycle-aware and manages automatic subscription. ViewModels are described as data holders for UI controllers that survive configuration changes. Room provides object mapping for SQLite to reduce boilerplate code. The document outlines how activities, fragments, ViewModels, repositories, and data sources fit together in the Android architecture.

1. Android Architecture Components
July 1, 2017

2. Architecture
Components
Lifecycles
Lifecycle-aware observables
Lightweight ViewModel
Object mapping for sqlite
2

3. A New Hero Emerges
3

4. @Override
protected void onStart() {
super.onStart();
Sensor.observe(...);
requests.observe(...);
expensiveFoo.start(...);
whenDoesThisEnd.pleaseSaveMe
();
}
@Override
protected void onStop() {
super.onStop();
Sensors.removeObserver(...);
request.cancel(...);
expensiveFoo.stop();
}
Lifecycles
whenDoesThisEnd.iForgotThisCall();
4

5. public abstract class Lifecycle {
@MainThread
public abstract void addObserver(LifecycleObserver observer);
@MainThread
public abstract void removeObserver(LifecycleObserver observer);
@MainThread
public abstract State getCurrentState();
@SuppressWarnings("WeakerAccess")
public enum Event {
....
}
@SuppressWarnings("WeakerAccess")
public enum State {
....
}
}
5

6. public enum Event {
ON_CREATE,
ON_START,
ON_RESUME,
ON_PAUSE,
ON_STOP,
ON_DESTROY,
ON_ANY
}
public enum State {
DESTROYED,
INITIALIZED,
CREATED,
STARTED,
RESUMED;
public boolean isAtLeast(State state) {
return compareTo(state) >= 0;
}
}
6

7. 7

8. LifecycleOwner
LifecycleObserver
8

9. public interface LifecycleOwner {
/**
* Returns the Lifecycle of the provider.
*
* @return The lifecycle of the provider.
*/
Lifecycle getLifecycle();
}
9

10. public class LifecycleActivity extends FragmentActivity implements LifecycleRegistryOwner {
private final LifecycleRegistry mRegistry = new LifecycleRegistry(this);
public LifecycleActivity() {
}
public LifecycleRegistry getLifecycle() {
return this.mRegistry;
}
}
public class LifecycleFragment extends Fragment implements LifecycleRegistryOwner {
LifecycleRegistry mLifecycleRegistry = new LifecycleRegistry(this);
public LifecycleFragment() {
}
public LifecycleRegistry getLifecycle() {
return this.mLifecycleRegistry;
}
}
10

11. public class LocationActivity extends LifecycleActivity {
private MyLocationListener myLocationListener;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
myLocationListener = new MyLocationListener(getApplicationContext(),
getLifecycle(), location -> {
});
}
}
No more onStart and onStop
11

12. public class MyLocationListener implements LifecycleObserver {
private Context context;
private LocationListener locationListener;
private Lifecycle lifecycle;
MyLocationListener(Context context, Lifecycle lifecycle, LocationListener locationListener) {
this.context = context;
this.locationListener = locationListener;
this.lifecycle = lifecycle;
this.lifecycle.addObserver(this);
}
@OnLifecycleEvent(Lifecycle.Event.ON_START) void onStart() {
//Start listener
}
@OnLifecycleEvent(Lifecycle.Event.ON_STOP) void onStop() {
//Stop listener
}
@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY) void cleanUp() {
this.lifecycle.removeObserver(this);
}
interface LocationListener {
void onLocationChange(Location location);
}
}
12

13. ON_CREATE ON_START addObserver
ON_CREAT
E
ON_START
Activity’s perspective
Observer’s
13

14. ON_CREATE ON_START addObserver
ON_CREAT
E
ON_START
Activity’s perspective
Observer’s
ON_RESUME
14
ON_RESUME

15. E ON_START addObserver
ON_CREAT
E
ON_START
Activity’s perspective
Observer’s
ON_RESUME
15
ON_PAUSE

16. LiveData<T>
An observable data holder
Lifecycle aware
Automatic subscription management
16

17. @Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
LiveData<Location> locationLiveData = //get from outside the World;
locationLiveData.observe(this, location -> {
});
}
17
This is LifecycleOwner

18. public class LocationData extends LiveData<Location> {
@Override
protected void onActive() {
super.onActive();
}
@Override
protected void onInactive() {
super.onInactive();
}
}
18

19. public class LocationData extends LiveData<Location> {
private LocationManager locationManager;
public LocationData(Context context) {
this.locationManager = (LocationManager)
context.getSystemService(Context.LOCATION_SERVICE);
}
private LocationListener locationListener = (location) -> {
this.setValue(location);
};
}
19

20. public class LocationData extends LiveData<Location> {
private LocationManager locationManager;
public LocationData(Context context) {
this.locationManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
}
private LocationListener locationListener = (location) -> {
this.setValue(location);
};
@Override protected void onActive() {
super.onActive();
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0 , 0, locationListener);
}
@Override protected void onInactive() {
super.onInactive();
locationManager.removeUpdates(locationListener);
}
}
20

21. MutableLiveData<Location> mutableLiveData = new
MutableLiveData<>();
public LiveData<Location> getLocation() {
return this.mutableLiveData;
}
21

22. LiveData<User> userData;
@Override
protected void onCreate(@Nullable Bundle
savedInstanceState) {
super.onCreate(savedInstanceState);
userData = webservice.fetchUser(...);
userData.observe(this, user -> {
//update UI
});
}
22
And then configuration change

23. ViewModel
Data holder for UI Controllers
23

24. public class MyViewModel extends ViewModel {
private LiveData<User> userData;
public LiveData<User>getUser() {
if (userData == null) {
loadUsers();
}
return userData;
}
private void loadUsers() {
// do async operation to fetch users
}
}
24

25. @Override
protected void onCreate(@Nullable Bundle
savedInstanceState) {
super.onCreate(savedInstanceState);
ViewModelProviders.of(this).get(MyViewModel.class)
.getUser().observe(this, user -> {
//Update UI
});
}
25

26. public abstract class ViewModel {
/**
* This method will be called when this ViewModel is no
longer used and will be destroyed.
* <p>
* It is useful when ViewModel observes some data and you
need to clear this subscription to
* prevent a leak of this ViewModel.
*/
@SuppressWarnings("WeakerAccess")
protected void onCleared() {
}
}
26

27. Persistence
27

28. SQLite
Share Preferences
28

29. 29

30. Hi
ROOM!
30

31. @Dao
interface FeedDao {
@Query("SELECT id, tiitle, subTitile FROM feed where title = :keyword")
List<Feed> loadFeed(String keyword);
}
@Entity
class Feed {
int id;
String title;
String subTitle;
}
31
@Database(entities = {Feed.class}, version 1)
abstract class MyDatabase extends RoomDatabase {
abstract FeedDao feedDao();
}

32. MyDatabase db = Room.databaseBuilder(getApplicationContext(),
MyDatabase.class)
.build();
db.feedDao().loadFeed(“xxxxx”);
32

33. @Query("SELECT id, tiitle, subTitile FROM Feeds where title = :keyword")
List<Feed> loadFeed(String keyword);
33
[SQLITE_ERROR] SQL error or missing database (no such table: feeds)
@Query("SELECT id, tiitle, subTitile FROM Feed where title = :keyword")
List<String> loadFeed(String keyword);
Error:(16, 18) error: Not sure how to convert a Cursor to this method’s return
type

34. Android Architecture
34

35. UI Controller (activities & fragments)
35
View Model
Repository
Data Sources

36. UI Controller
(activities & fragments)
36
View Model
Repository
Data Sources
● Activities & Fragments
● Observers the ViewModel
● Keeps the UI up-to-date
● Forwards user Actions back to
the ViewModel
● Prepares & keeps the data for the
UI
● Includes LiveData, Observables
etc
● Survives configuration changes
● The gateway for the Ul Controller
● The complete data model for the
App
● Provides simple data modification
& retrieval APIs
● API to the data sources
● E.g Retrofit for a REST API
● Room or Share preferences

37. UI Controller (activities & fragments)
37
View Model
Repository
Data Sources
Mock View Model
LiveData
Android Instrumentation Test with Espresso

38. 38
ViewModel
Mock Repository
Android JUnit Test

39. 39
Repository
Mock DataSource
Android JUnit Test

40. THANK YOU ~!
Email : khoatd19192@gmail.com
Skype : khoatd191
40