Advanced Dagger talk from 360andev

@NYTDevs | developers.nytimes.com
Mike Nakhimovich @FriendlyMikhail
Android Framework Team
Swordfighting with Dagger
Dependecy Injection Made Less Simple

What is Dagger?
Alternative way to instantiate and manage your
objects
● Guice - Google (Dagger v.0)
● Dagger 1 - Square
● Dagger 2 - Back to Google :-)

Why Do We Need It?
Good Code = Testable Code

Why Do We Need It?
More Tests = Less Anxiety

Why Do We Need It?
Proper Code Organization is
a requirement for testing

Untestable Code (Me in the Beginning)
public class MyClass {
private Model model;
public MyClass() {this.model = new Model();}
public String getName() {return model.getName();}
}
How can we test if model.getName() was called?

Internet Told Me to Externalize My Dependencies
public class MyClass {
...
public MyClass(Model model) {this.model = model;}
public String getName() {return model.getName();}
}...
public void testGetData(){
Model model = mock(Model.class);
when(model.getName()).thenReturn("Mike");
MyClass myClass = new MyClass(model).getName();
verify(myClass.getName()).isEq("Mike");
}

Where Does Model Come From?
Dependency Injection
to the rescue!

Dagger Helps You Externalize Object Creation
@Provides
Model provideModel(){
return new Model();
}

Provide from Modules
@Module
public class AppModule{
}
A module is a part of your application that provides some
functionality.

Provide from Modules
@Module
public class AppModule{
@Provides
Model provideModel(){
return new Model();
}
...
A module is a part of your application that provides some
functionality.

Components are Composed of Modules
@Singleton
@Component(modules = {MyModule.class})
public interface AppComponent {
void inject(MyActivity activity);
}
A Component is the manager of all your module providers

Next, Create a Component Instance
component = DaggerAppComponent.builder()
.myModule(new MyModule(this))
.build();

Register with Component
protected void onCreate(Bundle savedInstanceState) {
getApplicationComponent().inject(this);

Injection Fun
Now you can inject dependencies as fields or
constructor arguments
@Inject
Model model;
@Inject
public Presenter(Model model)

Dagger @ NY Times
Now for the
fun stuff!
50% Recipes 50% Ramblings

Dagger @ NY Times
● Module/Component Architecture
○ Working with libraries
○ Build Types & Flavors
● Scopes
○ Application
○ Activity (Now with Singletons!)
● Testing
○ Espresso
○ Unit Testing

Code Organization
How Dagger manages 6 build variants & 6+ libraries
GoogleDebug
AmazonDebug
GoogleBetaAmazonBeta
GoogleRelease
AmazonRelease

Application Scoped Modules
● App Module
● Build Type Module
● Library Module
● Flavor Module

App Module Singletons
○ Parser (configured GSON)

○ IO Managers

○ IO Managers
○ Configs (Analytics,AB, E-Commerce)

Example Library Module: E-Commerce
@Module
public class ECommModule {
@Provides
@Singleton
public ECommBuilder provideECommBuilder( )

E-Comm using App Module’s Dep
@Module
public class ECommModule {
@Provides
@Singleton
public ECommBuilder provideECommBuilder(ECommConfig config){
return new ECommManagerBuilder().setConfig(config);
}

Amazon & Google Flavors
● Amazon Variants needs Amazon E-Commerce
● Google Variants needs to contain Google E-Commerce
How can Dagger help?

E-Comm Qualified Provider
@Module public class ECommModule {
@Provides @Singleton
}
@Provides @Singleton @Google
public ECommManager providesGoogleEComm (ECommBuilder builder,
GooglePayments googlePayments)

E-Comm Qualified Provider
@Module public class ECommModule {
@Provides @Singleton
}
...
@Provides @Singleton @Amazon
public ECommManager providesAmazonEComm (ECommBuilder builder,
AmazonPayments amazonPayments)

Flavor Module: src/google & src/Amazon
@Module public class FlavorModule {
}

Flavor Module Provides Non-Qualified E-Comm
@Module public class FlavorModule {
@Singleton
@Provides
ECommManager provideECommManager(@Google ECommManager ecomm)
}
Note: Proguard strips out the other impl from Jar :-)

Type Module
Brings build specific dependencies/providers in Type Module

Type Module
○ Logging
■ Most logging for Beta Build
■ No-Op Release

Type Module
○ Logging
■ No-Op Release
○ Payments
■ No-Op for debug

Type Module
● Brings build specific dependencies/providers in Type Module
○ Logging
■ No-Op Release
○ Payments
■ No-Op for debug
○ Device ID
■ Static for Debug

Component Composition
How we combine our modules

Start with Base Component
● Base Component lives in src/main
● Contains inject(T t) for classes & Services that register
with Dagger (non flavor/build specific)
interface BaseComponent {
void inject(NYTApplication target);
}

Src/Google & Src/Amazon Contain a FlavorComponent
● Create FlavorComponent that inherits from BaseComponent
● Register inject for flavor specific classes
● Anything not in src/flavor that needs component registers here ie:
○ Messaging Service
○ Payment Activity
public interface FlavorComponent extends BaseComponent {
void inject(ADMessaging target);
}

App Component debug, beta, release
One for src/debug src/beta src/release
public interface ApplicationComponent {
}

App Component
Inherits from Flavor Component
public interface ApplicationComponent extends FlavorComponent {
}

App Component
● Adds @Component @Singleton annotations
@Singleton @Component
}

App Component
● Adds modules
@Singleton @Component(modules =
{ApplicationModule.class, FlavorModule.class, TypeModule.class,
AnalyticsModule.class, ECommModule.class, PushClientModule.class })
}

Anything registering with App Component
gains access to all providers for the Flavor/Type

Usage of Generated App
Component

App Component Factory
public class ComponentFactory {
public AppComponent buildComponent(Application context) {
return componentBuilder(context).build();
}
// We override it for functional tests.
DaggerApplicationComponent.Builder componentBuilder(Application context) {
return DaggerApplicationComponent.builder()
.applicationModule(new ApplicationModule(context)}
}

Component Instance
● NYT Application retains component
private void buildComponentAndInject() {
appComponent = componentFactory().buildComponent(this);
appComponent.inject(this);
}
public ComponentFactory componentFactory() {
return new ComponentFactory();
}

Activity Component
● Inherits all “provides” from App Component
● Allows you to add “Activity Singletons”
○ 1 Per Activity
○ Many views/fragments within activity can inject same
instance

ActivityComponent
@Subcomponent(modules = {ActivityModule.class, BundleModule.class})
@ScopeActivity
public interface ActivityComponent {
void inject(ArticleView view);
}
Add to AppComponent:
Activitycomponent plusActivityComponent(ActivityModule activityModule);

ActivityComponentFactory
public final class ActivityComponentFactory {
public static ActivityComponent create(Activity activity) {
return ((NYTApp)activity.getApplicationContext).getComponent()
.plusActivityComponent(new ActivityModule(activity));
}
}

Activity Component Injection
public void onCreate(@Nullable Bundle savedInstanceState) {
activityComponent = ActivityComponentFactory.create(this);
activityComponent.inject(this);

Activity Module
● Publish Subjects (mini bus)
● Reactive Text Resizer
● Snack Bar Util

Font Resizing
@Provides @ScopeActivity @FontBus
PublishSubject<Integer> provideFontChangeBus() {
return PublishSubject.create();
}
@Provides @ScopeActivity
FontResizer provideFontResize( @FontBus PublishSubject<Integer> fontBus) {
return new FontResizer(fontBus);
}

Usage of Font Resizer
@Inject
FontResizer fontResizer;
private void registerForFontResizing(View itemView) {
fontResizer.registerResize(itemView);
}

Usage of Font Resize “Bus”
@Inject
public SectionPresenter(@FontBus PublishSubject<Integer> fontBus) {
fontBus.subscribe(fontSize -> handleFontHasChanged());
}
Dagger helps us inject only what we need

SnackBarUtil
@ScopeActivity
public class SnackbarUtil {
@Inject Activity activity;
public Snackbar makeSnackbar(String txt, int duration) {
return Snackbar.make(...);}
}
….
In some presenter class:
public void onError(Throwable error) {
snackbarUtil.makeSnackbar(SaveHandler.SAVE_ERROR, SHORT).show();
}

Bundle Management
Passing intent arguments to fragments/views is painful
● Need to save state
● Complexity with nested fragments
● Why we not inject intent arguments instead?

Create Bundle Service
public class BundleService {
private final Bundle data;
public BundleService(Bundle savedState, Bundle intentExtras) {
data = new Bundle();
if (savedState != null) {
data.putAll(savedState);
}
if (intentExtras != null) {
data.putAll(intentExtras);
}
}

Instantiate Bundle Service in Activity
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
bundleService = new BundleService(savedInstanceState, getIntent().getExtras
());
//Never have to remember to save instance state again!
protected void onSaveInstanceState(Bundle outState) {
outState.putAll(bundleService.getAll());

Bind Bundle Service to Bundle Module
@Provides
@ScopeActivity
public BundleService provideBundleService(Activity context)
{
return ((Bundler) context).getBundleService();
}

Provide Individualized Intent Values
@Provides
@ScopeActivity
@AssetId
public Long provideArticleId(BundleService bundleService) {
return bundleService.get(ArticleActivity.ASSET_ID);
}

Inject Intent Values Directly into Views & Presenters
@Inject
public CommentPresenter(@AssetId String assetId){
//fetch comments for current article
}

Old Way
Normally we would have to pass assetId from:
ArticleActivity to
ArticleFragment to
CommentFragment to
CommentView to
CommentPresenter
:-l

Simple Testing
JUNIT Mockito, AssertJ
@Mock
AppPreferences prefs;
@Before public void setUp() {
inboxPref = new InboxPreferences(prefs);
}
@Test
public void testGetUserChannelPreferencesEmpty() {
when(prefs.getPreference(IUSER_CHANNELS,emptySet())) .thenReturn(null);
assertThat(inboxPref.getUserChannel()).isEmpty();
}

Dagger BaseTestCase
public abstract class BaseTestCase extends TestCase {
protected TestComponent getTestComponent() {
final ApplicationModule applicationModule = getApplicationModule();
return Dagger2Helper.buildComponent(
TestComponent.class,
applicationModule));}

TestComponent
@Singleton
@Component(modules = {TestModule.class,ApplicationModule.class,
FlavorModule.class, TypeModule.class, AnalyticsModule.class, EcommModule.
class, PushModule.class})
public interface TestComponent {
void inject(WebViewUtilTest test);

Dagger Test with Mocks
public class WebViewUtilTest extends BaseTestCase {
@Inject NetworkStatus networkStatus;
@Inject WebViewUtil webViewUtil;
protected ApplicationModule getApplicationModule() {
return new ApplicationModule(application) {
protected NetworkStatus provideNetworkStatus() {
return mock(NetworkStatus.class);
}
};
}

Dagger Test with Mocks
public class WebViewUtilTest extends BaseTestCase {
@Inject NetworkStatus networkStatus;
@Inject WebViewUtil webViewUtil;
…
@Test
public void testNoValueOnOffline() throws Exception {
when(networkStatus.isInternetConnected()).thenReturn(false);
webViewUtil.getIntentLauncher().subscribe(intent -> {fail("intent was launched");});}

Dagger Test with Mocks Gotchas
● Must have provides method
● Must be in module you are explicitly passing into Dagger

NYTFunctionalTestApp
● Creates Component with overridden providers

● Mostly no-op since this is global
■ Analytics
■ AB Manager
■ Other Test impls (network, disk)

■ Analytics
■ AB Manager
● Functional test runner uses custom FunctTestApp

■ Analytics
■ AB Manager
● Functional test runner uses custom FunctTestApp
● Test run end to end otherwise

public class NYTFunctionalTestsApp extends NYTApplication {
ComponentFactory componentFactory(Application context) {
return new ComponentFactory() {
protected DaggerApplicationComponent.Builder componentBuilder(Application context) {
return super.componentBuilder(context)
.applicationModule(new ApplicationModule(NYTFunctionalTestsApp.this) {
protected ABManager provideABManager() {
return new NoOpABManager();
}

NYTFunctionalTestRunner
public class NYTFunctionalTestsRunner extends AndroidJUnitRunner {
@Override
public Application newApplication(ClassLoader cl,String className, Context context)
{ return newApplication(NYTFunctionalTestsApp.class, context);
}
}

Sample Espresso Test
@RunWith(AndroidJUnit4.class)
public class MainScreenTests {
@Test
public void openMenuAndCheckItems() {
mainScreen
.openMenuDialog()
.assertMenuDialogContainsItemWithText(R.string.dialog_menu_font_resize)
.assertMenuDialogContainsItemWithText(R.string.action_settings);
}

Questions?

Thank You!
(We’re hiring)
@FriendlyMikhail

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