Java 使用匕首2时Dao为空
当我在presenter中调用DAO时,它返回null并导致NPE。 这里有一些代码: 刀类Java 使用匕首2时Dao为空,java,android,android-room,dagger-2,Java,Android,Android Room,Dagger 2,当我在presenter中调用DAO时,它返回null并导致NPE。 这里有一些代码: 刀类 @Dao public interface ElementsDao { @Query("SELECT * FROM `elements`") Flowable<List<Elements>> getAll(); @Insert Maybe<Long> insert(Elements element);... }
@Dao
public interface ElementsDao {
@Query("SELECT * FROM `elements`")
Flowable<List<Elements>> getAll();
@Insert
Maybe<Long> insert(Elements element);...
}
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(在清单中声明)
主持人
@InjectViewState
public class ActivityElementsPresenter extends MvpPresenter<ActivityElementsView> {
@Inject
ElementsDao elementsDao;
public void addElement(Elements element){
elementsDao.insert(element).subscribeOn(Schedulers.io())...
在调试时,我在presenter中设置了一个点,发现dao没有初始化
尝试使用类似于
App.getAppComponent().elementsDao()的东西代码>但它也起作用。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())...
}
}
您可以添加AppDatabase
类的代码吗?不在这里,添加到您的问题中,这里不可读。@rahat抱歉,问题已更新您如何获得ActivityElementsPresenter
的实例?您可以添加MvpPresenter
的代码吗,MvpPresenter
是所有演示者的基类吗?是的,这就是问题所在,现在感谢每一位演示者,您必须向AppComponent添加一个抽象方法,并在构造函数中调用inject
方法。如果您使用BasePresenter模式,那么注入将更容易。
@InjectViewState
public class ActivityElementsPresenter extends MvpPresenter<ActivityElementsView> {
@Inject
ElementsDao elementsDao;
public void addElement(Elements element){
elementsDao.insert(element).subscribeOn(Schedulers.io())...
@Database(entities = {Elements.class}, version = 1, exportSchema = false)
@TypeConverters({Converters.class})
public abstract class AppDatabase extends RoomDatabase {
public abstract ElementsDao getElementsDao();
//...
}
@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())...
}
}
@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.
}