Dagger 2依赖关系图不完整

Sandah Aung 发表于 Dev

桑达昂

我正在使用Dagger 2在我的新Android应用程序中注入依赖项。我想在服务中注入一个道。

模块：

@Module
public class DenkoStationModule {
    @Provides
    @Singleton
    public DenkoStationDao provideDenkoStationDao() {
        DaoMaster daoMaster = new DaoMaster(DenkoApplication.getDatabase());
        DaoSession daoSession = daoMaster.newSession();
        Log.d("dao", "station dao created");
        return daoSession.getDenkoStationDao();
    }

    @Provides
    @Singleton
    public DenkoStationService provideDenkoStationService() {
        Log.d("service", "station service created");
        return new DenkoStationService();
    }
}

服务：

public class DenkoStationService {

    private DenkoStationDao denkoStationDao;

    @Inject
    public void setDenkoStationDao(DenkoStationDao denkoStationDao) {
        this.denkoStationDao = denkoStationDao;
    }

    public List<DenkoStation> fetchAllDenkoStations() {
        Log.d("service", "loading all");
        return denkoStationDao.loadAll();
    }
}

成分：

@Singleton
@Component(modules = {DenkoStationModule.class})
public interface DenkoStationComponent {

    DenkoStationService provideDenkoStationService();
}

我从这样的活动中使用它：

DenkoStationComponent denkoStationComponent = Dagger_DenkoStationComponent.builder().denkoStationModule(new DenkoStationModule()).build();
        DenkoStationService denkoStationService = denkoStationComponent.provideDenkoStationService();

        List<DenkoStation> denkoStations = denkoStationService.fetchAllDenkoStations();

看起来dao没有被注入。

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.List org.bitbucket.infovillafoundation.denko.dao.DenkoStationDao.loadAll()' on a null object reference
            at org.bitbucket.infovillafoundation.denko.service.DenkoStationService.fetchAllDenkoStations(DenkoStationService.java:23)
            at org.bitbucket.infovillafoundation.denko.activity.HomeActivity.onCreate(HomeActivity.java:29)
            at android.app.Activity.performCreate(Activity.java:5933)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

当使用依赖项注入解决方案时，您希望框架也注入依赖项的依赖项。是框架问题还是我做错了什么？

康拉德·克拉科维克（Konrad Krakowiak）

Dagger 2使用注释处理器如果要在对象中注入某些东西，则必须在使用实例之前调用负责注入的方法。您有初始化的地方Component吗？如果没有任何地方，则必须这样做。

在组件内部创建初始化器，如下所示：

@Singleton
@Component(modules = {DenkoStationModule.class})
public interface DenkoStationComponent {


    public final static class Initializer {

        public static HierarchyViewerComponent init() {
            return Dagger_DenkoStationComponent.builder()
                    .denkoStationModule(new DenkoStationModule()) //it is not necessary because DenkoStationModule doesn't have params
                    .build();
        }

        void inject(DenkoStationService deviceInfoProvider);

    }
 }

之后，您必须通过方法初始化Component：

DenkoStationComponent.Initializer.init();

应用程序对象是执行此操作的好地方。并且您必须保留此实例（它可以是静态的）。

现在，您可以注入dao对象，如下所示：

public class DenkoStationService {

   @Inject
   DenkoStationDao denkoStationDao;

    @Override
    public void onCreate() {
        super.onCreate();
        //lines below are responsible for inject your object

        //use line below if you keep component instance in some object 
        //ObjectWhichContainsComponent.methodToGetComponent().inject(this);
        //or
        DenkoStationComponent.Initializer.init().inject(this);

        //if you didn't initialise component before

    }

    public List<DenkoStation> fetchAllDenkoStations() {
        Log.d("service", "loading all");
        return denkoStationDao.loadAll();
    }
}