无法用Dagger 2注入课程

Question

我正在尝试将Dagger 2添加到我的Android项目中.我想我理解了构建图形的概念.那时我正在黑暗中拍摄,这就是我出错的地方.
所有内容都会编译,但在运行时注入的字段为空.

我试图通过将Presenter注入我的MainActivity来开始.我已经编写了以下代码,并希望得到一些帮助,找出我出错的地方.

我的PresenterModule.java:

@Module
public class PresenterModule {

  @Provides MainActivityPresenter providesMainActivityPresenter() {
    return new DefaultMainActivityPresenter();
  }
}

我的Application类,它还包含遵循Dagger2示例代码的Component:

public class App extends Application {

  private PresenterComponent component;

  @Singleton
  @Component(modules = PresenterModule.class)
  public interface PresenterComponent {
    void inject(App app);
    void inject(MainActivity activity);
  }


  @Override public void onCreate() {
    Log.d("App.java", "Starting Application");
    super.onCreate();

    component = DaggerApp_PresenterComponent.builder()
        .presenterModule(new PresenterModule())
        .build();
    component.inject(this);
  }

  public PresenterComponent component() {
    return component;
  }
}

最后我的MainActivity.

public class DefaultMainActivity
    extends ActionBarActivity
    implements MainActivity
{
  @Inject MainActivityPresenter mPresenter;

@Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    ((App)getApplication()).component().inject(this);

    mPresenter.getCurrentDetailLineNumber();
    setContentView(R.layout.base_layout);

    getSupportActionBar();

    mContainer = (Container) findViewById(R.id.container);
    mPresenter.requestCurrentScreen();
  }

要注入的实际对象是接口的实现,但另一方面是POJO对象:

public class DefaultMainActivityPresenter implements MainActivityPresenter {

  private static final int SCREEN_BROWSER = 0;
  private static final int SCREEN_DETAIL = 1;

  LineNumber mCurrentDetailLineNumber;
  int mCurrentScreen;

  @Inject
  public DefaultMainActivityPresenter() {
  }
  ...
}

Answer 1

将PresenterComponent更改为以下将解决您的问题:

  @Singleton
  @Component(modules = PresenterModule.class)
  public interface PresenterComponent {
    void inject(App app);
    void inject(DefaultMainActivity activity);
  }

这是由于协方差:虽然类型的成员注入方法将接受其子类型的实例,但只会注入参数类型的注入注释成员及其超类型; 亚型的成员不会.例如,给定以下类型,当将一个实例传递给members-injection方法injectSelf(Self实例)时,只将a和b注入到Child的实例中:

   class Parent {
     @Inject A a;
   }

   class Self extends Parent {
     @Inject B b;
   }

   class Child extends Self {
     @Inject C c;
   }