Dependency Injection with Dagger 2 Miroslaw Stanek

about.me/froger_mcs @froger_mcs Head of mobile @ Azimo

Why should I use DI?

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Without DI class UserManager {
 private ApiService apiService;
 private UserStore userStore;
 
 public UserManager() {
 this.apiService = new ApiSerivce();
 this.userStore = new UserStore();
 }
 
 void registerUser() {/* */}
 }
 
 class RegisterActivity extends Activity {
 
 private UserManager userManager;
 
 @Override
 protected void onCreate(Bundle b) {
 this.userManager = new UserManager();
 }
 
 public void onRegisterClick(View v) {
 userManager.registerUser();
 }
 } class UserManager {
 private ApiService apiService;
 private UserStore userStore;
 
 public UserManager(ApiService apiService,
 UserStore userStore) {
 this.apiService = apiService;
 this.userStore = userStore;
 }
 
 void registerUser() {/* */}
 }
 
 class RegisterActivity extends Activity {
 
 private UserManager userManager;
 
 @Override
 protected void onCreate(Bundle b) {
 ApiService api = ApiService.getInstance();
 UserStore store = UserStore.getInstance();
 this.userManager = 
 new UserManager(api, store);
 }
 
 public void onRegisterClick(View v) {
 userManager.registerUser();
 }
 } With DI

Without DI class UserManager {
 private ApiService apiService;
 private UserStore userStore;
 
 public UserManager() {
 this.apiService = new ApiSerivce();
 this.userStore = new UserStore();
 }
 
 void registerUser() {/* */}
 }
 
 class RegisterActivity extends Activity {
 
 private UserManager userManager;
 
 @Override
 protected void onCreate(Bundle b) {
 this.userManager = new UserManager();
 }
 
 public void onRegisterClick(View v) {
 userManager.registerUser();
 }
 } class UserManager {
 private ApiService apiService;
 private UserStore userStore;
 
 public UserManager(ApiService apiService,
 UserStore userStore) {
 this.apiService = apiService;
 this.userStore = userStore;
 }
 
 void registerUser() {/* */}
 }
 
 class RegisterActivity extends Activity {
 
 private UserManager userManager;
 
 @Override
 protected void onCreate(Bundle b) {
 ApiService api = ApiService.getInstance();
 UserStore store = UserStore.getInstance();
 this.userManager = 
 new UserManager(api, store);
 }
 
 public void onRegisterClick(View v) {
 userManager.registerUser();
 }
 } With DI

Without DI With DI

Why DI is bad?

• DI requires a lot of boilerplate • Code hard to trace • Dependency injection frameworks are slow

Dependency Injection frameworks

DI example LoginActivity LoginActivityPresenter UserManager ApiService SharedPreferences UserDataStore

DI example (without DI framework) public class LoginActivity extends AppCompatActivity {
 
 LoginActivityPresenter presenter;
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 
 OkHttpClient okHttpClient = new OkHttpClient();
 RestAdapter.Builder builder = new RestAdapter.Builder();
 builder.setClient(new OkClient(okHttpClient))
 RestAdapter restAdapter = builder.build();
 
 ApiService apiService = restAdapter.create(ApiService.class);
 UserManager userManager = UserManager.getInstance(apiService);
 UserDataStore userDataStore = UserDataStore.getInstance(
 getSharedPreferences("prefs", MODE_PRIVATE)
 );
 
 presenter = new LoginActivityPresenter(this, userManager, userDataStore);
 }
 }

DI example LoginActivity LoginActivityPresenter UserManager ApiService SharedPreferences UserDataStore RegisterActivity RegisterActivityPresenter UserManager ApiService SharedPreferences UserDataStore

DI example (without Dagger) public class LoginActivity extends AppCompatActivity {
 
 LoginActivityPresenter presenter;
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 
 OkHttpClient okHttpClient = new OkHttpClient();
 RestAdapter.Builder builder = new RestAdapter.Builder();
 builder.setClient(new OkClient(okHttpClient))
 RestAdapter restAdapter = builder.build();
 
 ApiService apiService = restAdapter.create(ApiService.class);
 UserManager userManager = UserManager.getInstance(apiService);
 UserDataStore userDataStore = public class RegisterActivity extends AppCompatActivity {
 
 RegisterActivityPresenter presenter;
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 
 OkHttpClient okHttpClient = new OkHttpClient();
 RestAdapter.Builder builder = new RestAdapter.Builder();
 builder.setClient(new OkClient(okHttpClient))
 RestAdapter restAdapter = builder.build();
 
 ApiService apiService = restAdapter.create(ApiService.class);
 UserManager userManager = UserManager.getInstance(apiService);
 UserDataStore userDataStore = UserDataStore.getInstance(
 getSharedPreferences("prefs", MODE_PRIVATE)
 );
 
 presenter = new RegisterActivityPresenter(this, userManager, userDataStore);
 }
 } 2x

DI example public class LoginActivity extends AppCompatActivity {
 
 @Inject
 LoginActivityPresenter presenter;
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState); 
 getDependenciesGraph().inject(this);
 }
 }

DI example (with Dagger 2) public class LoginActivity extends AppCompatActivity {
 
 @Inject
 LoginActivityPresenter presenter;
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState); 
 DaggerSplashActivityComponent.builder()
 .appComponent(getAppComponent())
 .splashActivityModule(new SplashActivityModule(this))
 .build()
 .inject(this);
 }
 }

DI example (with Dagger 2) public class LoginActivity extends AppCompatActivity {
 
 @Inject
 LoginActivityPresenter presenter;
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState); 
 DaggerSplashActivityComponent.builder()
 .appComponent(getAppComponent())
 .splashActivityModule(new SplashActivityModule(this))
 .build()
 .inject(this);
 }
 }

No more instantiation.

DI framework cons (historical perspective)

• Performance (reflection usage) • Runtime graph validation • Instantiation magic (no source code)

Dagger 1 All problems gone!

• No reflection in object instantiation • Compile-time validation and instantiation • Source code for inject adapters

Almost all problems gone…

Dagger 1 flaws

Generated source code @Singleton
 public class AnalyticsManager {
 
 private Application app;
 
 @Inject
 public AnalyticsManager(Application app) {
 this.app = app;
 }
 }

Generated source code public final class AnalyticsManager$$InjectAdapter extends Binding
 implements Provider {
 private Binding app;
 
 public AnalyticsManager$$InjectAdapter() {
 super("frogermcs.io.githubclient.utils.AnalyticsManager", "members/ frogermcs.io.githubclient.utils.AnalyticsManager", IS_SINGLETON, AnalyticsManager.class);
 }
 
 @Override
 @SuppressWarnings("unchecked")
 public void attach(Linker linker) {
 app = (Binding) linker.requestBinding("android.app.Application", AnalyticsManager.class, getClass().getClassLoader());
 }
 
 @Override
 public void getDependencies(Set> getBindings, Set> injectMembersBindings) {
 getBindings.add(app);
 }
 
 @Override
 public AnalyticsManager get() {
 AnalyticsManager result = new AnalyticsManager(app.get());
 return result;
 }
 }

Proguard -dontwarn dagger.internal.codegen.** 
 -keepclassmembers,allowobfuscation class * {
 @javax.inject.* *;
 @dagger.* *;
 ();
 } 
 -keep class dagger.* { *; }
 -keep class javax.inject.* { *; }
 -keep class * extends dagger.internal.Binding
 -keep class * extends dagger.internal.ModuleAdapter
 -keep class * extends dagger.internal.StaticInjection

Proguard Process: frogermcs.io.githubclient, PID: 32685 java.lang.RuntimeException: Unable to create application frogermcs.io.githubclient.App: java.lang.IllegalStateException: Module adapter for class frogermcs.io.githubclient.app.b could not be loaded. Please ensure that code generation was run for this module. at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4556) … at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) Caused by: java.lang.IllegalStateException: Module adapter for class frogermcs.io.githubclient.b could not be loaded. Please ensure that code generation was run for this module. at dagger.internal.h.a(Unknown Source) at dagger.internal.h.a(Unknown Source) at dagger.internal.r.b(Unknown Source) at dagger.internal.g.a(Unknown Source) at dagger.internal.t.a(Unknown Source)

Reflection, Runtime graph composition • „Reflection is used to figure out how everything fits together”
 
 (DAGGER 2 - A New Type of dependency injection - https://www.youtube.com/watch?v=oK_XtfXPkqw ) • Runtime graph composition

Dagger 1 API public abstract class ObjectGraph {
 public static ObjectGraph create(Object... modules);
 public abstract ObjectGraph plus(Object... modules);
 public abstract T get(Class type);
 public abstract T inject(T instance);
 public abstract void validate();
 public abstract void injectStatics();
 }
 
 public @interface Module {
 Class>[] injects() default { };
 Class>[] staticInjections() default { };
 Class>[] includes() default { };
 Class> addsTo() default Void.class;
 boolean overrides() default false;
 boolean complete() default true;
 boolean library() default false;
 }
 
 public @interface Provides {
 }
 
 public interface Lazy {
 T get();
 }
 
 public interface MembersInjector {
 void injectMembers(T instance);
 }

Dagger 2 Silver bullet?

Dagger 2 • 100% Proguard friendly • Generates fully traceable code • Easy to read generated code (as close to hand- written code as possible) • Performance

Dagger 2 API public @interface Component {
 Class>[] modules() default {};
 Class>[] dependencies() default {};
 }
 
 public @interface Subcomponent {
 Class>[] modules() default {};
 }
 
 public @interface Module {
 Class>[] includes() default {};
 }
 
 public @interface Provides {
 }
 
 public @interface MapKey {
 boolean unwrapValue() default true;
 }
 
 public interface Lazy {
 T get();
 }

Dagger 1 API public abstract class ObjectGraph {
 public static ObjectGraph create(Object... modules);
 public abstract ObjectGraph plus(Object... modules);
 public abstract T get(Class type);
 public abstract T inject(T instance);
 public abstract void validate();
 public abstract void injectStatics();
 }
 
 public @interface Module {
 Class>[] injects() default { };
 Class>[] staticInjections() default { };
 Class>[] includes() default { };
 Class> addsTo() default Void.class;
 boolean overrides() default false;
 boolean complete() default true;
 boolean library() default false;
 }
 
 public @interface Provides {
 }
 
 public interface Lazy {
 T get();
 }
 
 public interface MembersInjector {
 void injectMembers(T instance);
 }

DI with Dagger 2 fundamentals

@Inject JSR-330

@Inject (constructor injection) public class LoginActivityPresenter {
 private LoginActivity loginActivity;
 private UserDataStore userDataStore;
 private UserManager userManager;
 
 @Inject
 public LoginActivityPresenter(LoginActivity loginActivity, 
 UserDataStore userDataStore, 
 UserManager userManager) {
 this.loginActivity = loginActivity;
 this.userDataStore = userDataStore;
 this.userManager = userManager;
 }
 } JSR-330

@Inject (fields injection) public class LoginActivity extends AppCompatActivity {
 
 @Inject
 LoginActivityPresenter presenter;
 @Inject
 AnalyticsManager analyticsManager; 
 @Override
 protected void onCreate(Bundle bundle) {
 super.onCreate(bundle);
 getAppComponent().inject(this);
 }
 } JSR-330

@Inject (method injection) public class LoginActivityPresenter {
 private LoginActivity loginActivity;
 
 @Inject
 public LoginActivityPresenter(LoginActivity loginActivity) {
 this.loginActivity = loginActivity;
 this.userDataStore = userDataStore;
 } @Inject
 public void enableWatches(Watches watches) {
 watches.register(this);
 }
 } JSR-330

@Module @Module
 public class GithubApiModule {
 
 @Provides
 @Singleton
 OkHttpClient provideOkHttpClient() {
 OkHttpClient okHttpClient = new OkHttpClient();
 okHttpClient.setConnectTimeout(60 * 1000, TimeUnit.MILLISECONDS);
 okHttpClient.setReadTimeout(60 * 1000, TimeUnit.MILLISECONDS);
 return okHttpClient;
 }
 
 @Provides
 @Singleton
 RestAdapter provideRestAdapter(Application application, OkHttpClient okHttpClient) {
 RestAdapter.Builder builder = new RestAdapter.Builder();
 builder.setClient(new OkClient(okHttpClient))
 .setEndpoint(application.getString(R.string.endpoint));
 return builder.build();
 }
 } Dagger 2

@Provide Dagger 2 @Module
 public class GithubApiModule {
 
 @Provides
 @Singleton
 OkHttpClient provideOkHttpClient() {
 OkHttpClient okHttpClient = new OkHttpClient();
 okHttpClient.setConnectTimeout(60 * 1000, TimeUnit.MILLISECONDS);
 okHttpClient.setReadTimeout(60 * 1000, TimeUnit.MILLISECONDS);
 return okHttpClient;
 }
 
 @Provides
 @Singleton
 RestAdapter provideRestAdapter(Application application, OkHttpClient okHttpClient) {
 RestAdapter.Builder builder = new RestAdapter.Builder();
 builder.setClient(new OkClient(okHttpClient))
 .setEndpoint(application.getString(R.string.endpoint));
 return builder.build();
 }
 }

@Component @Singleton
 @Component(
 modules = {
 AppModule.class,
 GithubApiModule.class
 }
 )
 public interface AppComponent {
 void inject(GithubClientApplication githubClientApplication);
 
 Application getApplication();
 
 AnalyticsManager getAnalyticsManager();
 
 UserManager getUserManager();
 
 } Dagger 2

@Component @ActivityScope
 @Component(
 modules = SplashActivityModule.class,
 dependencies = AppComponent.class
 )
 public interface SplashActivityComponent {
 SplashActivity inject(SplashActivity splashActivity);
 
 SplashActivityPresenter presenter();
 } Dagger 2

@Scope @Scope
 public @interface PerActivity { 
 } JSR-330 Scoping example http://fernandocejas.com/2015/04/11/tasting- dagger-2-on-android/ Implementation

@MapKey @MapKey(unwrapValue = true)
 @interface TestKey {
 String value();
 } @Provides(type = Type.MAP)
 @TestKey("foo")
 String provideFooKey() {
 return "foo value";
 }
 
 @Provides(type = Type.MAP)
 @TestKey("bar")
 String provideBarKey() {
 return "bar value";
 } @Inject
 Map map; map.toString() => „{foo=foo value, bar=bar value}” Dagger 2 Definition Usage

@Qualifier @Provides
 @Singleton
 @GithubRestAdapter //Qualifier
 RestAdapter provideRestAdapter() {
 return new RestAdapter.Builder()
 .setEndpoint("https://api.github.com")
 .build();
 }
 
 @Provides
 @Singleton
 @FacebookRestAdapter //Qualifier
 RestAdapter provideRestAdapter() {
 return new RestAdapter.Builder()
 .setEndpoint("https://api.facebook.com")
 .build();
 } JSR-330

@Qualifier @Inject
 @GithubRestAdapter
 RestAdapter githubRestAdapter;
 
 @Inject
 @FacebookRestAdapter
 RestAdapter facebookRestAdapter; JSR-330

Dagger 2 API public @interface Component {
 Class>[] modules() default {};
 Class>[] dependencies() default {};
 }
 
 public @interface Subcomponent {
 Class>[] modules() default {};
 }
 
 public @interface Module {
 Class>[] includes() default {};
 }
 
 public @interface Provides {
 }
 
 public @interface MapKey {
 boolean unwrapValue() default true;
 }
 
 public interface Lazy {
 T get();
 }

App example

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Source code https://github.com/frogermcs/GithubClient

Problems & doubts

• Scoping • Testing 
 https://github.com/google/dagger/issues/110 • Dagger 1 vs Dagger 2

QA

• GithubClient source code
 https://github.com/frogermcs/GithubClient • DAGGER 2 - A New Type of dependency injection
 https://www.youtube.com/watch?v=oK_XtfXPkqw • Dagger 1 to 2 migration process
 http://frogermcs.github.io/dagger-1-to-2-migration/ • The Future of Dependency Injection with Dagger 2
 https://www.parleys.com/tutorial/the-future-dependency-injection- dagger-2

mirek@azimo.com