java - Dagger 2 组件依赖性不起作用

Question

Dagger 模块

@Module
public class NetModule {

    @Provides
    @Singleton
    Gson provideGson() {
        GsonBuilder gsonBuilder = new GsonBuilder();
        return gsonBuilder.create();
    }

    @Provides
    @Singleton
    OkHttpClient provideOkHttpClient() {
        OkHttpClient client = new OkHttpClient();
        return client;
    }

    @Provides
    @Singleton
    Retrofit provideRetrofit(Gson gson, OkHttpClient okHttpClient) {
        Retrofit retrofit = new Retrofit.Builder()
                .addConverterFactory(GsonConverterFactory.create(gson))
                .baseUrl(BuildConfig.SERVER_BASE_URL)
                .client(okHttpClient)
                .build();
        return retrofit;
    }
}

@Module
public class AppModule{

    private Application application;

    public AppModule(Application application){
        this.application = application;
    }

    @Provides
    @Singleton
    Application provideApplication() {
        return application;
    }
}

@Module
public class ImageModule {

    @Provides
    @Singleton
    Picasso providePicasso(Application application, OkHttpClient client) {
        Picasso.Builder builder = new Picasso.Builder(application);
        builder.downloader(new OkHttp3Downloader(client));
        return builder.build();
    }

}

这些是组件

@Singleton
@Component(modules={NetModule.class})
public interface NetComponent {

    void inject(MyFragment fragment);
}

@Singleton
@Component(modules={AppModule.class, ImageModule.class}, dependencies = {NetModule.class})
public interface ImageComponent {

    void inject(MyFragment fragment);
}

这就是我注册组件的方式

public class MyApp extends Application{

    @Override
    public void onCreate() {

        netComponent = DaggerNetComponent.builder()
                .netModule(new NetModule())
                .build();

        imageComponent = DaggerImageComponent.builder()
                .appModule(new appModule(this))
                .imageModule(new ImageModule())
                .build();

    }

}

在 fragment 中

public class MyFragment extends Fragment {

   @Inject
   Retrofit retrofit;

   @Inject
   Picasso picasso;

  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container,   
     Bundle savedInstanceState) {

   ((MyApp)getActivity().getApplication()).getNetComponent().inject(this);

   ((MyApp)getActivity().getApplication()).getImageComponent().inject(this);
  ....

  }


}

编译错误如下

Error:(25, 10) error: com.squareup.picasso.Picasso cannot be provided without an @Inject constructor or from an @Provides- or @Produces-annotated method.

在 Dagger 2 中实现此目标的最佳方法是什么？

Answer 1

当组件 A 依赖于类型 B 时，您是说 B 上的每个零参数 getter 都将在 A 的图中可用。这意味着您不需要在 NetComponent 上单独调用 inject，但您需要在 NetComponent 的定义中公开 OkHttpClient。

这意味着 NetComponent 看起来像这样:

@Singleton
@Component(modules={NetModule.class})
public interface NetComponent {
    /** Exposes OkHttpClient. Used by components depending on NetComponent. */
    OkHttpClient getOkHttpClient();
}

而您的 onCreateView 可能如下所示:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,   
    Bundle savedInstanceState) {

  ((MyApp)getActivity().getApplication()).getImageComponent().inject(this);

}

在内部，Dagger 在两个单独的步骤中生成 DaggerNetComponent 和 DaggerImageComponent，但让 ImageComponent 调用新的 getOkHttpClient 方法。这也意味着 DaggerImageComponent 可以接受 NetComponent 的任何实现，而不仅仅是 Dagger 生成的实现。

相关资源:

• > What is the purpose of the non-inject methods in Components in Dagger 2? (参见 David Rawson 的回答)
• > Dagger 2 subcomponents vs component dependencies
• component dependencies 上的 Dagger 文档及其指向 provision methods 的链接