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Architecture Components
Constantine Mars
Team Lead, Senior Developer @ DataArt
Построение современной архитектуры
мобильных приложений
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Background
Software Architecture Basics
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Components:
-Activities
-Fragments
-Services
-Content Providers
-Broadcast Receivers
Android Has “Good Bones”
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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
There are Everyday Problems to Solve
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Simply related to Activity Lifecycle
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-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
Common Principles for staying in mind :)
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Image from fernandocejas.com
Separation of Concerns...
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Image from fernandocejas.com
Clean Architecture
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-Modular app
-Each class responsible for one well-defined function
-Should be no god objects
-The app should be testable
Remember Good Architecture Goals...
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Android Recommended Architecture
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Android Recommended Architecture. Another View
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Be together. not the same
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“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.”
Be together. not the same
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Building blocks
Architecture Components
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Purpose: Display data and pass on UI events
Neither contain the UI data, nor directly manipulate data
Examples: Activity, Fragment
Views = UI Controllers = LifecycleOwners
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After the lifecycles API in the Architecture Components becomes
stable, the Fragment class in the Android Support Library will
implement LifecycleOwner
LifecycleActivity, LifecycleFragment
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ViewModel
Data holder for Activity/Fragment
Survives configuration changes
NEVER references View / Activity / Fragment
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ViewModel
public class DetailActivityViewModel extends ViewModel {
private WeatherEntry mWeather;
public DetailActivityViewModel() {}
public WeatherEntry getWeather() { return mWeather; }
public void setWeather(WeatherEntry weatherEntry) { mWeather = weatherEntry; }
}
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ViewModel and Lifecycle
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ViewModel and LifecycleOwner
public class DetailActivity extends LifecycleActivity {
DetailActivityViewModel viewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
viewModel = ViewModelProviders.of(this).get(DetailActivityViewModel.class);
}
...
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Represent data needed for the UI to display
An observable data holder
Lifecycle aware
Automatic subscription management
LiveData
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Observer pattern. Subscription = Observation
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LiveData sample implementation
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Live Data
public class DetailActivityViewModel extends ViewModel {
private MutableLiveData mWeather;
public DetailActivityViewModel() {}
public MutableLiveData getWeather() {
return mWeather;
}
public void setWeather(WeatherEntry weatherEntry) {
mWeather.postValue(weatherEntry);
}
}
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Live Data observing
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); }
});
}
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-Single source of truth
-ViewModels simply request data
from the repository
-Is a mediator between
the different data sources
Repository pattern
Image from fernandocejas.com
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Manages data from a remote data
source, such as the internet
May use REST, Cloud
Remote Network Data Source
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Manages local data stored in the
database
Model
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Each class in the diagram only
stores a reference to the class or
classes directly "below it" and not
any classes above it
Layered architecture pattern
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ORM from Google
Room
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-Less boilerplate compared to the built-in APIs
-Compile-time validation of SQL queries
-Data observation via LiveData, RxJava
Room ORM purposes
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-@Entity
-@Dao
-@Database
Room annotations
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Entity
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@Entity declaration
@Entity(tableName = "weather",
indices = {@Index(value = {"date"}, unique = true)})
public class WeatherEntry {
@PrimaryKey(autoGenerate = true)
private int id;
…
}
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@Entity constructors
//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
...
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Dao
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@Dao declaration
@Dao
public interface WeatherDao {
@Query("SELECT * FROM weather") List getAll();
@Insert(onConflict = OnConflictStrategy.REPLACE)
void insertAll(WeatherEntry... weatherEntries);
@Delete void delete(WeatherEntry weatherEntry);
}
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Database
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@Database declaration
@Database(entities = {WeatherEntry.class}, version = 1)
@TypeConverters(DateConverter.class)
public abstract class AppDatabase extends RoomDatabase {
public abstract WeatherDao weatherDao();
}
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@Database - a singleton
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;
}
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Type converters
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();
}
}
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Alternatives
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Repository
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Repository pattern
public class WeatherRepository {
public synchronized static WeatherRepository getInstance();
public synchronized void initializeData();
private void deleteOldData();
private boolean isFetchNeeded();
private void startFetchWeatherService();
}
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Repository - fetch data from network
mWeatherNetworkDataSource = weatherNetworkDataSource;
LiveData networkData = mWeatherNetworkDataSource.getCurrentWeatherForecasts();
networkData.observeForever(newForecastsFromNetwork -> {
mExecutors.diskIO().execute(() -> {
mWeatherDao.bulkInsert(newForecastsFromNetwork);
Log.d(LOG_TAG, "New values inserted");
});
});
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Repository - use LiveData
private WeatherNetworkDataSource(Context context, AppExecutors executors) {
mContext = context;
mExecutors = executors;
mDownloadedWeatherForecasts = new MutableLiveData();
}
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Check when to fetch
private boolean isFetchNeeded() {
Date today = CustomDateUtils.getNormalizedUtcDateForToday();
int count = mWeatherDao.countAllFutureWeather(today);
return (count < WeatherNetworkDataSource.NUM_DAYS);
}
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Check when to fetch
public synchronized void initializeData() {
if (mInitialized) return;
mInitialized = true;
mExecutors.diskIO().execute(() -> {
if (isFetchNeeded()) {
startFetchWeatherService();
}
});
}
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Display the data
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And again - observe LiveData
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); }
});
}
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Testing
Sneak peek :)
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UI Controller - Instrumentation
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ViewModel - JUnit
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Repository - JUnit, MockWebServer
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Scalability and advices
Almost there...
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What if...
I use RxJava?
I already have MVP?
I love Kotlin?
I’m working on legacy project?
Typical questions
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The Answer is...
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Read, watch and visit...
Links
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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
What to read and watch :)
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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
Alternatives to consider
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Where to go :)
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Where to go :)
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Where to go :)
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Thank you! :)
Constantine Mars
@ConstantineMars
+ConstantineMars
Mobile Architecture Club