Dagger2 + Kotlin: lateinit property has not been i

问题:

I'm trying to inject the ViewModelFactory into my Activity, but it keeps throwing this same error: lateinit property viewModelFactory has not been initialized. I can't find what I may be doing wrong. See the code above from my classes

AppComponent.kt

@Component(modules = [(AppModule::class), (NetworkModule::class), (MainModule::class)])
interface AppComponent {

    fun inject(application: TweetSentimentsApplication)

    fun inject(mainActivity: MainActivity)

    fun context(): Context

    fun retrofit(): Retrofit
}

MainModule.kt

@Module
class MainModule {

    @Provides
    fun mainViewModelFactorty(repository: TweetRepository): MainViewModelFactory = MainViewModelFactory(repository)

    @Provides
    fun local(database: AppDatabase): TweetLocal = TweetLocal(database)

    @Provides
    fun remote(tweetService: TweetService): TweetRemote = TweetRemote(tweetService)

    @Provides
    fun tweetService(retrofit: Retrofit): TweetService = retrofit.create(TweetService::class.java)

    @Provides
    fun repository(local: TweetLocal, remote: TweetRemote): TweetRepository = TweetRepository(local, remote)

}

MainActivity.kt

class MainActivity : AppCompatActivity() {

    @Inject lateinit var viewModelFactory: MainViewModelFactory

    private val viewModel: MainViewModel? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.main_activity)

        ViewModelProviders.of(this, viewModelFactory).get(MainViewModel::class.java)

        viewModel?.init("guuilp")
        viewModel?.getTweetList()?.observe(this, Observer {
            Toast.makeText(this, it?.size.toString(), Toast.LENGTH_LONG).show()
        })
    }
}

TweetSentimentsApplication.kt

open class TweetSentimentsApplication: Application(){

    companion object {
        lateinit var appComponent: AppComponent
    }

    override fun onCreate() {
        super.onCreate()

        initDI()
    }

    private fun initDI() {
        appComponent = DaggerAppComponent.builder()
                .appModule(AppModule(this))
                .build()
    }
}

回答1:

You have to call the inject(mainActivity: MainActivity) method you've defined in AppComponent when you're initializing your MainActivity, that's how Dagger actually injects the dependencies you need.

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.main_activity)

    // This is where the dependencies are injected
    TweetSentimentsApplication.appComponent.inject(this)

    ViewModelProviders.of(this, viewModelFactory).get(MainViewModel::class.java)

    ...
}

回答2:

You can also do this:

  @Inject
  lateinit var viewModelFactory: ViewModelProvider.Factory
  val mainViewModel: MainViewModel by lazy {
      ViewModelProviders.of(this, viewModelFactory)[MainViewModel::class.java]
  }

and use abstract modules with @ContributesAndroidInjector for the activity, and abstract module for view model. Using abstract is more efficient:

   @Module
   abstract class AndroidBindingModule {

   @ContributesAndroidInjector
    internal abstract fun contributesAnActivity(): AnActivity
    }



 @Module
    abstract class ViewModelModule {
      //the default factory only works with default constructor
      @Binds
      @IntoMap
      @ViewModelKey(AViewModel::class)
      abstract fun bindArtViewModel(aViewModel: AViewModel): ViewModel

      @Binds
      abstract fun bindViewModelFactory(factory: AViewModelFactory): ViewModelProvider.Factory
    }





 @Documented
    @Target(AnnotationTarget.FUNCTION, AnnotationTarget.PROPERTY_GETTER, AnnotationTarget.PROPERTY_SETTER)
    @Retention(RetentionPolicy.RUNTIME)
    @MapKey
    internal annotation class ViewModelKey(val value: KClass<out ViewModel>)

回答3:

You can also do this:

  @Inject
  lateinit var viewModelFactory: ViewModelProvider.Factory
  val mainViewModel: MainViewModel by lazy {
      ViewModelProviders.of(this, viewModelFactory)[MainViewModel::class.java]
  }