170608(목) - DI with Dagger2

DI with Dagger2

Dagger API

- @Module + @Provides

mechanism for providing dependencies

- @Inject

mechanism for requesting dependencies

- @Component

bridge between modules and injections

- plus some other sugar, magic, and conventions.

Providing Dependencies

- modules는 methods가 dependencies를 제공하는 class

- @Module on the class.

- @Provides (and friends) on each method.

@Module

public class NetworkModule {

@Provides @Singleton

OkHttpClient prvideOkHttpClient() {

return new OkHttpClient();

}

@Provides @Singleton

TwitterApi provideTwitterApi(OkHttpClient client) {

return new TwitterApi(clent);

}

}

- Designed to be partitioned and composed together.

@Module

public class TwitterModule {

private final String user;

public TwitterModule(String user) {

this.user = user;

}

@Provides @Singleton

Tweeter prvideTweeter(TwitterApi api) {

return new Tweeter(api, user);

}

@Provides @Singleton

Timeline provideTimeline(TwitterApi api) {

return new Timeline(api, user);

}

}

- Tweeter를 시작하는것으로 예를 들면, Tweeter -> TwitterApi -> OkHttpClient 순으로 따라 올라가면서 DI를 요청한다.

- @Provides에서 제공된 객체를 가지고 올라왔던 길을 다시 내려가면서 DI를 진행한다.

- 이미 한번 DI가 진행됐으면 객체가 이미 존재하므로 굳이 최상단까지 올라가지 않더라도 DI 가능.

Requesting Dependencies

- @Inject annotation

- Constructor Injection

- @Inject on a single constructor

- parameters are dependencies

- Dependencies can be stored in private and final fields.

public class TwitterApplication {

private final Tweeter tweeter;

private final Timeline timeline;

@Inject

public TwitterApplication(Tweeter tweeter, Timeline timeline) {

this.tweeter = tweeter;

this.timeline = timeline;

}

...

}

- Implicitly made available for downstream injection.

@Module

public class NetworkModule {

@Provides @Singleton

OkHttpClient prvideOkHttpClient() {

return new OkHttpClient();

}

@Provides @Singleton

TwitterApi provideTwitterApi(OkHttpClient client) {

return new TwitterApi(clent);

}

}

@singleton

public class TwitterApi {

private final OkHttpClient client;

@Inject

public TwitterApi(OkHttpClient client) {

this.client = client;

}

public void postTweet(String user, String tweet) {

OkHttpClient client = new OkHttpClient();

Request request = ...

client.newCall(request).execute();

}

}

- Method Injection

- @Inject on methods

- Method parameters are dependencies

- Injection happens after object is fully instantiated.

- Only one valid use case: passing 'this' to a dependency.

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);

}

}

- Field Injection

- @Inject on fields for dependencies.

- Field may not be private or final.

- Injection happens after object is fully instantiated.

- Object is usually responsible for or aware of injection.

public class TwitterApplication {

@Inject Tweeter tweeter;

@Inject final Timeline timeline;

...

}

Components

- Bridge between modules and injection

- The injector.

@singleton

@Component(modules = {

NetworkModule.class,

TwitterModule.class,

})

public interface TwitterComponent {

Tweeter tweeter();

Timeline timeline();

}

TwitterComponent component = Dagger_TwitterComponent.builder()

.networkModule(new NetworkModule())

.twitterModule(new TwitterModule("신대규"))

.build();

Tweeter tweeter = component.tweeter();

tweeter.tweet("Hello, #Devoxx ~!");

Timeline timeline = component.timeline();

timeline.loadMore(20);

for (Tweet tweet : timeline.get()) {

System.out.println(tweet);

}

---

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 ~!");

timeline.loadMore(20);

for (Tweet tweet : timeline.get()) {

System.out.println(tweet);

}

}

}

@singleton

@Component(modules = {

NetworkModule.class,

TwitterModule.class,

})

public interface TwitterComponent {

TwitterApplication app();

}

TwitterComponent component = Dagger_TwitterComponent.builder()

.twitterModule(new TwitterModule("신대규"))

.build();

component.app().run();

---

public class TwitterApplication implements Runnable {

@inject Tweeter tweeter;

@inject Timeline timeline;

@Override

public void run() {

tweeter.tweet("Hello #Devoxx ~!");

timeline.loadMore(20);

for (Tweet tweet : timeline.get()) {

System.out.println(tweet);

}

}

}

@singleton

@Component(modules = {

NetworkModule.class,

TwitterModule.class,

})

public interface TwitterComponent {

void injectApp(TwitterApplication app);

}

TwitterComponent component = Dagger_TwitterComponent.builder()

.twitterModule(new TwitterModule("신대규"))

.build();

TwitterApplication app = new TwitterApplication();

component.injectApp(app);

app.run();

---

public class TwitterApplication implements Runnable {

@inject Tweeter tweeter;

@inject Timeline timeline;

@Override

public void run() {

tweeter.tweet("Hello #Devoxx ~!");

timeline.loadMore(20);

for (Tweet tweet : timeline.get()) {

System.out.println(tweet);

}

}

}

@singleton

@Component(modules = {

NetworkModule.class,

TwitterModule.class,

})

public interface TwitterComponent {

void injectActivity(TwitterActivity activity);

}

TwitterComponent component = Dagger_TwitterComponent.builder()

.twitterModule(new TwitterModule("신대규"))

.build();

TwitterActivity activity = ...;

component.injectActivity(activity);

---

public class TwitterApplication implements Runnable {

@inject Tweeter tweeter;

@inject Timeline timeline;

@Override

public void run() {

tweeter.tweet("Hello #Devoxx ~!");

timeline.loadMore(20);

for (Tweet tweet : timeline.get()) {

System.out.println(tweet);

}

}

}

@singleton

@Component(modules = {

NetworkModule.class,

TwitterModule.class,

})

public interface TwitterComponent {

void injectProcessor(Processor processor);

}

TwitterComponent component = Dagger_TwitterComponent.builder()

.twitterModule(new TwitterModule("신대규"))

.build();

TwitterProcessor processor = ...;

component.injectProcessor(processor);

---

@singleton

@Component(modules = {

NetworkModule.class,

TwitterModule.class,

})

public interface TwitterComponent {

TwitterApplication injectApp(TwitterApplication app);

}

TwitterComponent component = Dagger_TwitterComponent.builder()

.twitterModule(new TwitterModule("신대규"))

.build();

TwitterApplication app = new TwitterApplication();

component.injectApp(app).run();

- Implementation of scopes

- Singleton을 사용하면 component 생성시 create() 만으로도 build 가능

@Singleton

@component(modules = NetworkModule.calss)

public interface ApiComponent {

TwitterApi api();

}

@Singleton

@component(

dependencies = ApiComponent.class,

moduels = TwitterModule.class

}

public interface TwitterComponent {

TwitterApplication app();

}

@Module

public class TwitterModule {

private final String user;

public TwitterModule(String user) {

this.user = user;

}

@Provides @Singleton

Tweeter prvideTweeter(TwitterApi api) {

return new Tweeter(api, user);

}

@Provides @Singleton

Timeline provideTimeline(TwitterApi api) {

return new Timeline(api, user);

}

}

ApiComponent apiComponent = Dagger_ApiComponent.create();

TwitterComponent twitterComponent = Dagger_TwitterComponent.builder()

.apiComponent(apiComponent)

.twitterModule(new TWitterModule("신대규"))

.build();

- Scope Annotations

- Only create a single instance.

- @Singleton is the "largest" scope

- Custom annotations for semantic clarity, shorter lifetime.

@Scope

public @interface User {

}

@Module

public class TwitterModule {

private final String user;

public TwitterModule(String user) {

this.user = user;

}

@Provides @User

Tweeter prvideTweeter(TwitterApi api) {

return new Tweeter(api, user);

}

@Provides @User

Timeline provideTimeline(TwitterApi api) {

return new Timeline(api, user);

}

}

@User

@component(

dependencies = ApiComponent.class,

moduels = TwitterModule.class

}

public interface TwitterComponent {

TwitterApplication app();

}

- Under the Hood

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