Dao在使用Dagger2时为空

Question

当我在presenter中调用DAO时，它返回null并导致NPE。这里有一些代码:DAO类

@Dao
public interface ElementsDao {
@Query("SELECT * FROM   `elements`")
Flowable<List<Elements>> getAll();
@Insert
Maybe<Long> insert(Elements element);...
}

模块类:

@Module
public class DatabaseModule {
private AppDatabase appDatabase;
public DatabaseModule(Application mApplication){
appDatabase = Room.databaseBuilder(mApplication, AppDatabase.class,"dbWarehouse")
.setJournalMode(RoomDatabase.JournalMode.TRUNCATE)
.build();
}
@Singleton
@Provides
public AppDatabase provideDatabase(){
return appDatabase;
}
@Singleton
@Provides
ElementsDao providesElementsDao(AppDatabase appDatabase){
return appDatabase.getElementsDao();
}
}
@Module
public class AppModule {
Application mApplication;
public AppModule(Application application){
mApplication = application;
}
@Provides
@Singleton
Application providesApplication() {
return mApplication;
}
}

组件类

@Singleton
@Component(dependencies = {},modules = {AppModule.class, DatabaseModule.class})
public interface AppComponent {
void inject(MainActivity mainActivity);
void inject(ElementsActivity elementsActivity);
void inject(ActivityElementsPresenter activityElementsPresenter);
ElementsDao elementsDao();
AppDatabase appDatabase();
Application application();
}

应用程序类(在manifest中声明)

public class App extends Application {
private static AppComponent appComponent;
@Override
public void onCreate() {
super.onCreate();
initDagger();
}
private void initDagger(){
appComponent = DaggerAppComponent.builder()
.appModule(new AppModule(this))
.databaseModule(new DatabaseModule(this))
.build();
}
public static AppComponent getAppComponent() {
return appComponent;
}
}

和主持人

@InjectViewState
public class ActivityElementsPresenter extends MvpPresenter<ActivityElementsView> {
@Inject
ElementsDao elementsDao;
public void addElement(Elements element){
elementsDao.insert(element).subscribeOn(Schedulers.io())...

AppDatabase类

@Database(entities = {Elements.class}, version = 1, exportSchema = false)
@TypeConverters({Converters.class})
public abstract class AppDatabase extends RoomDatabase {
public abstract ElementsDao getElementsDao();
//...
}

调试时，我在演示器中设置了一个点，发现dao没有初始化elementsDao尝试使用App.getAppComponent().elementsDao();之类的东西，但它也可以正常工作。

Answer 1

你需要这样做，

@InjectViewState
public class ActivityElementsPresenter extends MvpPresenter<ActivityElementsView> {
@Inject
ElementsDao elementsDao;
public ActivityElementsPresenter(){
App.getAppComponent().inject(this);//calling the dagger's injector to inject dependency.
}
public void addElement(Elements element){
elementsDao.insert(element).subscribeOn(Schedulers.io())...
}
}

在

@Singleton
@Component(dependencies = {},modules = {AppModule.class, DatabaseModule.class})
public interface AppComponent {
void inject(MainActivity mainActivity);
void inject(ElementsActivity elementsActivity);
void inject(ActivityElementsPresenter activityElementsPresenter);//will inject dependency to ActivityElementsPresenter.  
}