Dependency Injection with Dagger 2

Presentation I gave at Google I/O Extended 2015 in @techspacekrk - www.meetup.com/GDG-Krakow/events/221822600/

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

Transcript

1. Dependency Injection
   with Dagger 2
   Miroslaw Stanek
   

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

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3. Why should I use DI?
   

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5. 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
   

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6. 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
   

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7. Without DI With DI
   

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8. Why DI is bad?
   

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

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10. Dependency Injection
    frameworks
    

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11. DI example
    LoginActivity
    LoginActivityPresenter
    UserManager
    ApiService SharedPreferences
    UserDataStore
    

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12. 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);

    }

    }
    

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

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14. 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
    

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15. DI example
    
    public class LoginActivity extends AppCompatActivity {

    

    @Inject

    LoginActivityPresenter presenter;

    

    @Override

    protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    

    getDependenciesGraph().inject(this);

    }

    }
    

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16. 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);

    }

    }
    

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17. 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);

    }

    }
    

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18. No more instantiation.
    

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19. DI framework cons
    (historical perspective)
    

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

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21. Dagger 1
    All problems gone!
    

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

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23. Almost all problems
    gone…
    

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24. Dagger 1 flaws
    

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25. Generated source code
    @Singleton

    public class AnalyticsManager {

    

    private Application app;

    

    @Inject

    public AnalyticsManager(Application app) {

    this.app = app;

    }

    }
    

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26. 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;

    }

    }
    

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27. 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
    

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28. 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)
    

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29. 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
    

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30. 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);

    }
    

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31. Dagger 2
    Silver bullet?
    

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

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33. 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();

    }
    

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34. 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);

    }
    

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35. DI with Dagger 2
    fundamentals
    

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36. @Inject
    JSR-330
    

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37. @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
    

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38. @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
    

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39. @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
    

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40. @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
    

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41. @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();

    }

    }
    

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42. @Component
    @Singleton

    @Component(

    modules = {

    AppModule.class,

    GithubApiModule.class

    }

    )

    public interface AppComponent {

    void inject(GithubClientApplication githubClientApplication);

    

    Application getApplication();

    

    AnalyticsManager getAnalyticsManager();

    

    UserManager getUserManager();

    

    }
    Dagger 2
    

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43. @Component
    @ActivityScope

    @Component(

    modules = SplashActivityModule.class,

    dependencies = AppComponent.class

    )

    public interface SplashActivityComponent {

    SplashActivity inject(SplashActivity splashActivity);

    

    SplashActivityPresenter presenter();

    }
    Dagger 2
    

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44. @Scope
    @Scope

    public @interface PerActivity {
    

    }
    JSR-330
    Scoping example
    http://fernandocejas.com/2015/04/11/tasting-
    dagger-2-on-android/
    Implementation
    

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45. @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
    

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46. @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
    

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47. @Qualifier
    @Inject

    @GithubRestAdapter

    RestAdapter githubRestAdapter;

    

    @Inject

    @FacebookRestAdapter

    RestAdapter facebookRestAdapter;
    JSR-330
    

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48. 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();

    }
    

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49. App example
    

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

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54. Problems & doubts
    

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55. • Scoping
    • Testing 

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

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56. QA
    

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57. • 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
    

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58. mirek@azimo.com
    

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