The document discusses Android architecture and architecture components. It recommends separating an app into modular components with clear responsibilities, such as activities, fragments, services, content providers and broadcast receivers. It also recommends the ViewModel component to survive configuration changes, LiveData for observable data, Room for local database access, repositories as a single source of truth, and testing each component individually. The Architecture Components provide common building blocks for app architecture including activities, fragments, ViewModel, LiveData and Room. The recommended architecture is a starting point but each app may have different needs.

1. Architecture Components
Build your app right way and enjoy IT! :)
Constantine Mars
Team Lead, Senior Developer @ DataArt

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Android Has “Good Bones”
Components:
-Activities
-Fragments
-Services
-Content Providers
-Broadcast Receivers

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But… There are Everyday Problems to Solve
App-hopping
OS may kill app at random time
App components lifecycle is not under control
Components should not depend on each other
Can’t rely on data, stored in components

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Simply related to Activity Lifecycle

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Common Principles for staying in the mind :)
-Separation of concerns
-Provide solid user experience
-Keep UI lean and simple
-Keep UI free of app logic
-Drive UI from model
-Use persistent model
-Assign clear responsibilities for each model class

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Focus on Separation of Concerns...
image from fernandocejas.com

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Consider Clean Architecture approach...
image from fernandocejas.com

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Remember Good Architecture Goals...
-Modular app
-Each class responsible for one well-defined function
-Should be no god objects
-The app should be testable

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And Finally - Android Recommended Architecture

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Android Recommended Architecture. Another View
image from Guide to App Architecture

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Be together. not the same

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Be together. not the same
“It is impossible to have one way of writing apps that will be the best for every
scenario. That being said, this recommended architecture should be a good
starting point for most use cases. If you already have a good way of writing
Android apps, you don't need to change.”
Quote from Guide to App Architecture

13. Architecture Components
Building blocks

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Views = UI Controllers = LifecycleOwners
Purpose: Display data and pass on UI events
Neither contain the UI data, nor directly manipulate
data
Examples: Activity, Fragment

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LifecycleActivity, LifecycleFragment
After the lifecycles API in the Architecture Components
becomes stable, the Fragment class in the Android
Support Library will implement LifecycleOwner

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ViewModel
Data holder for Activity/Fragment
Survives configuration changes
NEVER references View / Activity / Fragment

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public class DetailActivityViewModel extends ViewModel {
private WeatherEntry mWeather;
public DetailActivityViewModel() {}
public WeatherEntry getWeather() { return mWeather; }
public void setWeather(WeatherEntry weatherEntry) { mWeather = weatherEntry; }
}
ViewModel
extend ViewModel

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ViewModel and Lifecycle

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public class DetailActivity extends LifecycleActivity {
DetailActivityViewModel viewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
viewModel = ViewModelProviders.of(this).get(DetailActivityViewModel.class);
}
...
ViewModel and LifecycleOwner
Provider

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LiveData
Represent data needed for the UI to display
An observable data holder
Lifecycle aware
Automatic subscription management

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LiveData event propagation

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LiveData sample implementation

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public class DetailActivityViewModel extends ViewModel {
private MutableLiveData<WeatherEntry> mWeather;
public DetailActivityViewModel() {}
public MutableLiveData<WeatherEntry> getWeather() {
return mWeather;
}
public void setWeather(WeatherEntry weatherEntry) {
mWeather.postValue(weatherEntry);
}
}
Live Data
LiveData

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public class DetailActivity extends LifecycleActivity {
DetailActivityViewModel viewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
viewModel = ViewModelProviders.of(this).get(DetailActivityViewModel.class);
viewModel.getWeather().observe(this, weatherEntry -> {
if(weatherEntry!=null) { bindWeatherToUI(weatherEntry); }
});
}
Live Data observing
Observe

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Repository
-Single source of truth
-ViewModels simply request
data from the repository
-Is a mediator between the
different data sources
image from fernandocejas.com

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Remote Network Data Source
Manages data from a remote
data source, such as the
internet
May use REST, Cloud

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Model
Manages local data stored in
the database

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Layered architecture pattern
Each class in the diagram only
stores a reference to the class
or classes directly "below it" and
not any classes above it

29. Room
ORooM :)

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Room?

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Room ORM purposes
-Less boilerplate compared to the built-in APIs
-Compile-time validation of SQL queries
-Data observation via LiveData, RxJava

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Room annotations
-@Entity
-@Dao
-@Database

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@Entity

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@Entity(tableName = "weather",
indices = {@Index(value = {"date"}, unique = true)})
public class WeatherEntry {
@PrimaryKey(autoGenerate = true)
private int id;
…
}
@Entity declaration

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//Room constructor
public WeatherEntry(int id, int weatherIconId, Date date, ...) {
//Json constructor - ignored by Room
@Ignore
public WeatherEntry(int weatherIconId, Date date,
// (!) Only one constructor should be exposed to Room
...
@Entity constructors

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@Dao

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@Dao
public interface WeatherDao {
@Query("SELECT * FROM weather") List<WeatherEntry> getAll();
@Insert(onConflict = OnConflictStrategy.REPLACE)
void insertAll(WeatherEntry... weatherEntries);
@Delete void delete(WeatherEntry weatherEntry);
}
@Dao declaration

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@Database

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@Database(entities = {WeatherEntry.class}, version = 1)
@TypeConverters(DateConverter.class)
public abstract class AppDatabase extends RoomDatabase {
public abstract WeatherDao weatherDao();
}
@Database declaration

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private static final String DATABASE_NAME = "weather";
private static final Object LOCK = new Object();
private static volatile AppDatabase sInstance;
public static AppDatabase getInstance(Context context) {
if (sInstance == null) { synchronized (LOCK) {
if (sInstance == null) {
sInstance = Room.databaseBuilder(context.getApplicationContext(),
AppDatabase.class, AppDatabase.DATABASE_NAME).build();
}
}}
return sInstance;
}
@Database - a singleton

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class DateConverter {
@TypeConverter
public static Date toDate(Long timestamp) {
return timestamp == null ? null : new Date(timestamp);
}
@TypeConverter
public static Long toTimestamp(Date date) {
return date == null ? null : date.getTime();
}
}
Type converters

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Alternatives

43. Repository
Single source of trust

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public class WeatherRepository {
public synchronized static WeatherRepository getInstance();
public synchronized void initializeData();
private void deleteOldData();
private boolean isFetchNeeded();
private void startFetchWeatherService();
}
Repository pattern

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mWeatherNetworkDataSource = weatherNetworkDataSource;
LiveData<WeatherEntry[]> networkData =
mWeatherNetworkDataSource.getCurrentWeatherForecasts();
networkData.observeForever(newForecastsFromNetwork -> {
mExecutors.diskIO().execute(() -> {
mWeatherDao.bulkInsert(newForecastsFromNetwork);
Log.d(LOG_TAG, "New values inserted");
});
});
Repository - fetch data from network
Get and observe

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private WeatherNetworkDataSource(Context context, AppExecutors executors)
{
mContext = context;
mExecutors = executors;
mDownloadedWeatherForecasts = new
MutableLiveData<WeatherEntry[]>();
}
Repository - use LiveData
LiveData

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private boolean isFetchNeeded() {
Date today = CustomDateUtils.getNormalizedUtcDateForToday();
int count = mWeatherDao.countAllFutureWeather(today);
return (count < WeatherNetworkDataSource.NUM_DAYS);
}
Check when to fetch

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public synchronized void initializeData() {
if (mInitialized) return;
mInitialized = true;
mExecutors.diskIO().execute(() -> {
if (isFetchNeeded()) {
startFetchWeatherService();
}
});
}
Check when to fetch
Check if fetch needed

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Display the data

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public class DetailActivity extends LifecycleActivity {
DetailActivityViewModel viewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
viewModel = ViewModelProviders.of(this).get(DetailActivityViewModel.class);
viewModel.getWeather().observe(this, weatherEntry -> {
if(weatherEntry!=null) { bindWeatherToUI(weatherEntry); }
});
}
And again - observe LiveData

51. Testing
Sneak peek :)

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UI Controller - Instrumentation

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ViewModel - JUnit

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Repository - JUnit, MockWebServer

55. Latest updates
From Alpha to Beta

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September - October updates
October 5, 2017 - Beta 2
- improved LiveDataReactiveStreams,
- FullLifecycleObserver for Java 8,
- Handling @Query methods with @NonNull annotations,
- Still requires proguard settings to keep android.arch.lifecycle.GeneratedAdapter
1.0.0 Alpha 9-1
- Support Library 26.1.0, AppCompatActivity and Support Fragment now implement the
LifecycleOwner interface
- LifecycleActivity & LifecycleFragment are now deprecated
- New Library: Paging

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Paging Library
- DataSource,
- PagedList
- PagedListAdapter
- KeyedDataSource if you need to use data from item N-1 to load item N
- TiledDataSource
- LivePagedListProvider

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Paging Library - Annotations on DAO
@Query("select * from users WHERE age > :age order by name DESC, id ASC")
TiledDataSource<User> usersOlderThan(int age);
@Query("SELECT * from users order WHERE age > :age order by name DESC, id ASC")
public abstract LivePagedListProvider<Integer, User> usersOlderThan(int age);

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Paging Library - flow

60. Almost there...
Scalability

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Typical questions
What if...
I use RxJava?
I already have MVP?
I love Kotlin?
I’m working on legacy project?

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The Answer is...

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What to read :)
Guide to App Architecture https://developer.android.com/topic/libraries/architecture/guide.html
Architecture Components
https://developer.android.com/topic/libraries/architecture/index.html
I/O ‘17 Architecture Components Introduction - https://youtu.be/FrteWKKVyzI
Solving the Lifecycle Problem - https://youtu.be/bEKNi1JOrNs
Persistence and Offline - https://youtu.be/MfHsPGQ6bgE
Architecture Components on GDD Europe - https://youtu.be/Ts-uxYiBEQ8
GDD Europe CodeLabs g.co/codelabs/gdd17
Google Github samples https://github.com/googlesamples/android-architecture-components

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Alternatives to consider
Moxy https://github.com/Arello-Mobile/Moxy
Mosby https://github.com/sockeqwe/mosby
Android MVP Helper https://github.com/Ufkoku/AndroidMVPHelper
Clean Architecture https://github.com/android10/Android-CleanArchitecture
Reark https://github.com/reark/reark
MVP + Dagger2 + Rx https://android.jlelse.eu/mvp-dagger-2-rx-clean-modern-android-app-
code-74f63c9a6f2f
Architecture the Lost Years by Uncle Bob https://youtu.be/WpkDN78P884

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Where to go :)

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Where to go :)

67. Constantine Mars
@ConstantineMars
+ConstantineMars
Thank you!
Q&A Mobile Architecture Club