Android Dagger 2 POJO字段注入null

Question

刚开始使用Dagger 2,我对如何设置一切感到困惑.

我正在尝试注入一个POJO,但它总是为空.首先,一些代码:

App.java

private AppComponent appComponent;

@Override
public void onCreate() {
    super.onCreate();
    appComponent = DaggerAppComponent
            .builder()
            .appModule(new AppModule(this))
            .build();
}

public AppComponent component() {
    return appComponent;
}

AppModule.java

@Module
public class AppModule {
    private Application app;

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

    @Provides @Singleton
    public Application application() {
        return app;
    }
}

AppComponent.java

@Singleton
@Component(modules = AppModule.class)
public interface AppComponent {
    void inject(App application);
    Application application();
}

NetworkingManager.java

@Singleton
public class NetworkingManager {
    private Context ctx;

    @Inject
    public NetworkingManager(Context context) {
        this.ctx = context;
    }
}

NetModule.java

@Module
public class NetModule {
    @Provides @Singleton
    public NetworkingManager provideNetworkingManager(Application application) {
        return new NetworkingManager(application);
    }
}

NetComponent.java

@Singleton
@Component(modules = {NetModule.class},
        dependencies = {AppModule.class})
public interface NetComponent {
    void inject(NetworkingManager networkingManager);
}

SomeClass.java

@Inject
NetworkingManager networkingManager;

public void doSomethingWithNetworkManager() {
    networkManager.doStuff();
}

我花了很多时间查看大量的教程,SO问题和示例,但我无法弄清楚我做错了什么.

我99%肯定我有一些设置错误,但我无法弄清楚是什么.

Answer 1

根据您的评论,您希望NetworkingManager在您的应用程序中随处可用.

让我们从你的定义开始Component:

@Singleton
@Component(modules = AppModule.class)
public interface AppComponent {
    void inject(App application);
}

这告诉Dagger这个组件将注入App该类.现在,您还可以告诉Dagger您想要注入的其他课程.所以如果你想注入一个Activity例子,你会添加:

@Singleton
@Component(modules = AppModule.class)
public interface AppComponent {
    void inject(App application);
    void inject(MainActivity activity) //Where MainActivity is a class that extends Activity.
}

请注意,这不是IMO共享应用程序范围依赖关系的最佳方式; 你应该创建一个Component继承自AppComponent并AppComponent公开所需共享依赖项的东西.

现在让我们来看看你的模块类:

@Module
public class NetModule {
    @Provides @Singleton
    public NetworkingManager provideNetworkingManager(Application application) {
        return new NetworkingManager(application);
    }
}

在这里,你是@Provide荷兰国际集团一个NetworkingManager,那就是罚款.你NetworkingManager需要一个Application(一个Context真正的),为什么不提供App的内部NetworkingManager,甚至更好,为什么不提供？NetworkingManager里面的AppModule,因为AppModule应@Provide东西都是常见的全Application:

@Module
public class AppModule {
    private Application app;

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

    @Provides @Singleton
    public Application application() {
        return app;
    }

    @Provides @Singleton
    public NetworkingManager provideNetworkingManager(Application application) {
        return new NetworkingManager(application);
    }
}

现在在App课堂上:

public class App extends Application {
    private AppComponent appComponent;

@Override
public void onCreate() {
    super.onCreate();
    appComponent = DaggerAppComponent
            .builder()
            .appModule(new AppModule(this))
            .build();
   appComponent.inject(this);
}

public AppComponent component() {
    return appComponent;
 }
}

在我们的假设中MainActivity:

public class MainActivity extends Activity {

private AppComponent appComponent;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    appComponent = ((App)getApplicationContext()).getAppComponent();
    appComponent.inject(this);
   }
 }

看来你没有@Component(dependencies = {...})正确使用.dependencies当你想Component使用我上面提到的机制将依赖关系从一个暴露给另一个时使用.