Architecture components

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