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Android with Dagger 2 ⿈黃千碩 / Kros iOS/Android Developer

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Dependency Injection • 中⽂文 - 相依性注⼊入？ • No “new”, dependencies come to you.

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Dependency Injection • ⼀一種 Design Pattern • 最快速，且不⽤用任何 Liberary 即可達成 • 其實每個 app 中都已經有實作 DJ

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public class Tweeter {
 public void tweet(String tweet) { TwitterApi api = new TwitterApi(); api.postTweet("JakeWharton", tweet); } } public class TwitterApi {
 public void postTweet(String user, String tweet) { OkHttpClient client = new OkHttpClient(); Request request = // TODO build POST request… client.newCall(request).execute(); } Tweeter tweeter = new Tweeter();
 tweeter.tweet("Hello, #Devoxx 2014!");

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public class TwitterApi {
 private final OkHttpClient client = new OkHttpClient(); public void postTweet(String user, String tweet) { Request request = // TODO build POST request client.newCall(request).execute(); } }

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public class TwitterApi {
 private final OkHttpClient client; public TwitterApi(OkHttpClient client) { this.client = client; } public void postTweet(String user, String tweet) { Request request = // TODO build POST request client.newCall(request).execute(); } }

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public class Tweeter {
 private final TwitterApi api = new TwitterApi(new OkHttpClient());
 private final String user; public Tweeter(String user) { this.user = user; } public void tweet(String tweet) { api.postTweet(user, tweet);
 } }

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public class Tweeter {
 private final TwitterApi api = new TwitterApi(new OkHttpClient());
 private final String user; public Tweeter(String user) { this.user = user; } public void tweet(String tweet) { api.postTweet(user, tweet);
 } } Tweeter tweeter = new Tweeter("JakeWharton");
 tweeter.tweet("Hello, #Devoxx 2014!");
 tweeter.tweet("#Hungover #Dagger");


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Libraries • Spring • Guice • Dagger (v1) • PicoContainer • CDI

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Guice • Developed at Google by Bob Lee, later Jesse Wilson, others. • Adopted and maintained by Java Core Libraries team. Powerful, dynamic, well-tested, wide- spread, etc... • Configuration problems occur at runtime. • Slow initialization, slow injection, memory concerns.

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Dagger (v1) • Developed at Square by Jesse Wilson advised by Bob Lee. • Initially targeted at highly resource constrained environments. • Static analysis of all dependencies and injection points. • Fail as early as possible (compile-time, not runtime) • Eliminate reflection on methods, fields, and annotations.

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Dagger (v2) • Proposed and implemented by Java Core Libraries team. • Eliminate runtime library and generated code overhead. • Shift remaining runtime analysis to compile time. • Scoping with annotations and associated static analysis.

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Dagger API • @Module + @Provides: 提供相依性的機制 • @Inject: 要求提供相依性 • @Component: modules 與 injections 之間的橋 樑，讓兩者能互通 • 另外有⼀一些語法糖可以使⽤用，使⽤用起來更⽅方便 • 被設計成可以拆成許多⼩小元件，並組合起來使⽤用

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Providing Dependencies • Modules 是⼀一些 classes，⽽而這些 classes 中的 methods 提供相依性。 • 必須在 class 上加上 @Module • 必須在每個 method 上加上 @Provides

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public class NetworkModule { OkHttpClient provideOkHttpClient() { return new OkHttpClient(); } TwitterApi provideTwitterApi(OkHttpClient client) { return new TwitterApi(client); } }

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@Module public class NetworkModule { OkHttpClient provideOkHttpClient() { return new OkHttpClient(); } TwitterApi provideTwitterApi(OkHttpClient client) { return new TwitterApi(client); } }

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@Module public class NetworkModule { !@Provides OkHttpClient provideOkHttpClient() { return new OkHttpClient(); } @Provides TwitterApi provideTwitterApi(OkHttpClient client) { return new TwitterApi(client); } }

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@Module public class NetworkModule { !@Provides @Singleton OkHttpClient provideOkHttpClient() { return new OkHttpClient(); } @Provides @Singleton TwitterApi provideTwitterApi(OkHttpClient client) { return new TwitterApi(client); } }

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi

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Providing Dependencies • Modules 是⼀一些 classes，⽽而這些 classes 中的 methods 提供相依性。 • 必須在 class 上加上 @Module • 必須在每個 method 上加上 @Provides • Modules 可以拆開成很多 module，也可以組合在 ⼀一起使⽤用

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@Module
 public class TwitterModule { private final String user; public TwitterModule(String user) {
 this.user = user; } @Provides @Singleton Tweeter provideTweeter(TwitterApi api) { return new Tweeter(api, user); } @Provides @Singleton Timeline provideTimeline(TwitterApi api) { return new Tweeter(api, user); } }

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi TwitterModule#provideTweeter TwitterModule#provideTimeline Tweeter Timeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi TwitterModule#provideTweeter TwitterModule#provideTimeline Tweeter Timeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi TwitterModule#provideTweeter TwitterModule#provideTimeline Tweeter Timeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi TwitterModule#provideTweeter TwitterModule#provideTimeline Tweeter Timeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi TwitterModule#provideTweeter TwitterModule#provideTimeline Tweeter Timeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi Tweeter Timeline TwitterModule#provideTweeter TwitterModule#provideTimeline

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OkHttpClient Providing Dependencies NetworkModule#provideOkHttpClient TwitterApi NetworkModule#provideTwitterApi TwitterModule#provideTweeter TwitterModule#provideTimeline Tweeter Timeline

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Requesting Dependencies • 必須要有 @Inject 的 annotation • 有三種 inject ⽅方式 • Constructor, field, and method injection.

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Constructor Injection • 在 Constructor 加上 @Inject • 表⽰示 Constructor 的參數需要 dependency • 這些參數可以被使⽤用在 private 或 final fields.

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public class TwitterApplication { private final Tweeter tweeter; private final Timeline timeline; @Inject
 public TwitterApplication(Tweeter tweeter, Timeline timeline) {
 this.tweeter = tweeter; this.timeline = timeline;
 } //… }

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Method Injection • 在 methods 上加上 @Inject • 表⽰示 method 的參數需要 dependency • Injection 發⽣生在物件被完全建⽴立之後 • 只有⼀一個合理的 use case: passing ‘this’ to a dependency.

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public class TwitterApplication { private final Tweeter tweeter; private final Timeline timeline; @Inject
 public TwitterApplication(Tweeter tweeter, Timeline timeline) {
 this.tweeter = tweeter; this.timeline = timeline;
 } @Inject
 public void enableStreaming(Streaming streaming) {
 streaming.register(this); } }

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Field Injection • 在 fields 上加上 @Inject • Field 不能為 private 或是 final • Injection 發⽣生在物件被完全建⽴立之後 • 在 android 中最常⾒見到

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public class TwitterApplication extends Activity { @Inject Tweeter tweeter; @Inject Timeline timeline; // ...
 }

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Components • Modules 與 injections 之間的橋樑，讓兩者能互 通 • Component 為 injector，實際發⽣生 inject 的⼈人 • Scope 的概念

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@Singleton @Component(modules = { NetworkModule.class,
 TwitterModule.class,
 !})
 public interface TwitterComponent { 
 }

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@Singleton @Component(modules = { NetworkModule.class,
 TwitterModule.class,
 !})
 public interface TwitterComponent { Tweeter tweeter();
 Timeline timeline(); }

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TwitterComponent component = DaggerTwitterComponent.builder() .twitterModule(new TwitterModule(“JakeWharton")) .build();

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TwitterComponent component = DaggerTwitterComponent.builder() .twitterModule(new TwitterModule(“JakeWharton")) .build(); @Module
 public class TwitterModule { private final String user; public TwitterModule(String user) {
 this.user = user; } // …

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TwitterComponent component = DaggerTwitterComponent.builder() .twitterModule(new TwitterModule(“JakeWharton")) .build(); Tweeter tweeter = component.tweeter(); tweeter.tweet("Hello, #Devoxx 2014!");

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public class TwitterApplication implements Runnable {
 private final Tweeter tweeter;
 private final Timeline timeline; @Inject
 public TwitterApplication(Tweeter tweeter, Timeline timeline) {
 this.tweeter = tweeter; this.timeline = timeline;} @Override public void run() { tweeter.tweet("Hello #Devoxx 2014!”); timeline.loadMore(20);
 for (Tweet tweet : timeline.get()) { System.out.println(tweet); } } }

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@Singleton @Component(modules = { NetworkModule.class,
 TwitterModule.class,
 !})
 public interface TwitterComponent { TwitterApplication app(); }

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@Singleton @Component(modules = { NetworkModule.class,
 TwitterModule.class,
 !})
 public interface TwitterComponent { TwitterApplication app(); } TwitterComponent component = DaggerTwitterComponent.builder() .twitterModule(newTwitterModule(“JakeWharton")) .build(); component.app().run();

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public class TwitterApplication implements Runnable {
 @Inject Tweeter tweeter;
 @Inject Timeline timeline; @Inject
 public TwitterApplication(Tweeter tweeter, Timeline timeline) {
 this.tweeter = tweeter; this.timeline = timeline;} @Override public void run() { tweeter.tweet("Hello #Devoxx 2014!”); timeline.loadMore(20);
 for (Tweet tweet : timeline.get()) { System.out.println(tweet); } } }

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@Singleton @Component(modules = { NetworkModule.class,
 TwitterModule.class,
 !})
 public interface TwitterComponent { void injectApp(TwitterApplication app); }

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@Singleton @Component(modules = { NetworkModule.class,
 TwitterModule.class,
 !})
 public interface TwitterComponent { void injectApp(TwitterApplication app); } TwitterComponent component = DaggerTwitterComponent.builder() .twitterModule(newTwitterModule(“JakeWharton")) .build(); TwitterApplication app = new TwitterApplication();
 component.injectApp(app); app.run();

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@Singleton @Component(modules = { NetworkModule.class,
 TwitterModule.class,
 !})
 public interface TwitterComponent { void injectActivity(TwitterActivity activity); } TwitterComponent component = DaggerTwitterComponent.builder() .twitterModule(newTwitterModule(“JakeWharton")) .build(); TwitterActivity activity = // Android creates instance...
 component.injectActivity(activity); // use tweet and timeline in activity…

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Components • Modules 與 injections 之間的橋樑，讓兩者能互 通 • Component 為 injector，實際發⽣生 inject 的⼈人 • Scope 的概念

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@Component( dependencies = ApiComponent.class, modules = TwitterModule.class
 ) public interface TwitterComponent {
 void injectActivity(TwitterActivity activity); } @Singleton
 @Component(modules = NetworkModule.class) public interface ApiComponent { 
 }

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@Singleton
 @Component(modules = NetworkModule.class) public interface ApiComponent { TwitterApi api();
 } @Component( dependencies = ApiComponent.class, modules = TwitterModule.class
 ) public interface TwitterComponent {
 void injectActivity(TwitterActivity activity); }

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@Module
 public class TwitterModule { private final String user; public TwitterModule(String user) {
 this.user = user; } @Provides @Singleton Tweeter provideTweeter(TwitterApi api) { return new Tweeter(api, user); } @Provides @Singleton Timeline provideTimeline(TwitterApi api) { return new Tweeter(api, user); } }

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ApiComponent apiComponent = Dagger_ApiComponent.create(); TwitterComponent twitterComponent = DaggerTwitterComponent.builder() .apiComponent(apiComponent) .twitterModule(new TwitterModule("JakeWharton"))
 .build(); TwitterActivity activity = // Android creates instance...
 component.injectActivity(activity);

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Scope Annotations • Only create a single instance. • @Singleton 是最⼤大的 scope
 (可以想像是最上層的 scope) • ⾃自定 scope，可以讓程式更清楚，也可以有較短 的 lifecycle @Scope public @interface User {
 }

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@Module
 public class TwitterModule { private final String user; public TwitterModule(String user) {
 this.user = user; } @Provides Tweeter provideTweeter(TwitterApi api) { return new Tweeter(api, user); } @Provides Timeline provideTimeline(TwitterApi api) { return new Tweeter(api, user); } }

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@Module
 public class TwitterModule { private final String user; public TwitterModule(String user) {
 this.user = user; } @Provides @User Tweeter provideTweeter(TwitterApi api) { return new Tweeter(api, user); } @Provides @User Timeline provideTimeline(TwitterApi api) { return new Tweeter(api, user); } }

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@Component( dependencies = ApiComponent.class, modules = TwitterModule.class
 ) public interface TwitterComponent {
 void injectActivity(TwitterActivity activity); }

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@User @Component( dependencies = ApiComponent.class, modules = TwitterModule.class
 ) public interface TwitterComponent {
 void injectActivity(TwitterActivity activity); }

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Dagger 1 public abstract class ObjectGraph {
 public static ObjectGraph create(Object... modules) {}
 public abstract ObjectGraph plus(Object... modules);
 public abstract void validate();
 public abstract void injectStatics();
 public abstract T get(Class type);
 public abstract T inject(T instance); } 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 true; } public @interface Provides {
 enum Type { UNIQUE, SET }
 Type type() default Type.UNIQUE; } public interface Lazy {
 T get(); } public interface MembersInjector {
 void injectMembers(T instance); }

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

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Issues • Gained 13% of processor performance at google scale • No reflection at all • Less flexible

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Demo https://github.com/ch8908/djdemo

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Reference • DAGGER 2 - A New Type of dependency injection
 https://www.youtube.com/watch?v=oK_XtfXPkqw • Dependency Injection with Dagger 2
 https://speakerdeck.com/jakewharton/ dependency-injection-with-dagger-2-devoxx-2014 • The Future of Dependency Injection with Dagger 2
 https://www.parleys.com/tutorial/ 5471cdd1e4b065ebcfa1d557/