Kotlin和Room的匕首2错误

Question

我正在重构一个应用程序给Kotlin，目前我正面临来自Dagger的一个奇怪的错误。我试图实现一个MVVM设计，但我很难坚持匕首错误。

AppModule

@Module
class AppModule(val app: App) {

companion object {
    private var INSTANCE: RecorderisDB? = null

    private fun getInstance(context: Context): RecorderisDB?{
        if (INSTANCE == null) {
            synchronized(RecorderisDB::class){
                INSTANCE = Room.databaseBuilder(context.applicationContext,
                        RecorderisDB::class.java,
                        "recorderis.db")
                        .build()
            }
        }
        return INSTANCE
    }

    fun destroyInstance(){
        INSTANCE = null
    }
}

@Provides @Singleton
fun provideApp() = app

@Provides @Singleton @Nullable
fun getDB(context: Context): RecorderisDB? = getInstance(context)

@Provides @Singleton
fun provideDateVM(db: RecorderisDB): DateViewModel {
    return DateViewModel(db)
}

AppComponent

@Singleton
@Component(modules = [(AppModule::class)])
interface AppComponent {

fun inject(app: App)

fun inject(form: Form)
}

DateViewModel

class DateViewModel @Inject constructor(val dB: RecorderisDB){

fun createDate(name: String, symbol: String, date: String): Completable {
    return Completable.fromAction{ dB.getDateDao().newDate(Date(name, symbol, date))}
}

Form.kt

class Form : AppCompatActivity() {

@Inject
lateinit var dateVM: DateViewModel
public override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_form)
    App.graph.inject(this)

    initDialog()
    setUpRecyclerView()
 }

Stacktrace

英语不是我的第一语言，但是我认为这个错误是矛盾的吗？是不是告诉我我的DB不是可空的，而是被提供的？基本上，我在AppModule中拥有的是我的同伴对象。

15:27:21.882 [ERROR] [org.gradle.api.Task] e: C:\Users\diego\Apps\Recorderis\app\build\tmp\kapt3\stubs\debug\tech\destinum\recorderis\DI\AppComponent.java:13: 
error: [Dagger/Nullable] tech.destinum.recorderis.Data.RecorderisDB is not nullable, 
but is being provided by @org.jetbrains.annotations.Nullable @Singleton 
@Provides tech.destinum.recorderis.Data.RecorderisDB 
tech.destinum.recorderis.DI.AppModule.getDB(android.content.Context)
public abstract void inject(@org.jetbrains.annotations.NotNull()
                     ^
  tech.destinum.recorderis.Data.RecorderisDB is injected at
      tech.destinum.recorderis.DI.AppModule.provideDateVM(db)
  tech.destinum.recorderis.Data.ViewModels.DateViewModel is injected at
      tech.destinum.recorderis.activities.Form.dateVM
  tech.destinum.recorderis.activities.Form is injected at
      tech.destinum.recorderis.DI.AppComponent.inject(tech.destinum.recorderis.activities.Form)

Answer 1

它特别指出，问题在于您正在注入RecorderisDB，即使您正在提供RecorderisDB?。

解决方案是什么？Dagger已经通过使用@Singleton @Provides为您处理双重检查的锁定。根本不需要这样的代码。

@Module
class AppModule(val app: App) {

    @Provides
    fun provideApp() = app

    @Provides @Singleton
    fun getDB(context: App): RecorderisDB = Room.databaseBuilder(context.applicationContext,
                        RecorderisDB::class.java,
                        "recorderis.db")
                        .build()

    @Provides 
    // @Singleton // are you CERTAIN this is singleton?
    fun provideDateVM(db: RecorderisDB): DateViewModel {
        return DateViewModel(db)
    }
}