Kotlin dagger 2 Android ViewModel injection error

问题

I'm trying to use dagger 2 on my Android application to inject the new ViewModel from arch android library.

From what I see on this sample https://github.com/googlesamples/android-architecture-components/tree/e33782ba54ebe87f7e21e03542230695bc893818/GithubBrowserSample I need to use this:

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

@Module
abstract class ViewModelModule {
    @Binds
    @IntoMap
    @ViewModelKey(LoginViewModel::class)
    internal abstract fun bindLoginViewModel(viewModel: LoginViewModel): LoginViewModel

    @Binds
    @IntoMap
    @ViewModelKey(MainMenuViewModel::class)
    internal abstract fun bindSearchViewModel(viewModel: MainMenuViewModel): MainMenuViewModel

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

@ApplicationScope
@Component(modules = arrayOf(ApplicationModule::class, NetworkModule::class, ViewModelModule::class))
interface ApplicationComponent {
    fun plusActivityComponent(activityModule: ActivityModule): ActivityComponent
    fun inject(application: LISAApplication)

}

And my factory is:

@ApplicationScope
class ViewModelFactory @Inject constructor(private val creators: Map<Class<out ViewModel>, @JvmSuppressWildcards Provider<ViewModel>>) : ViewModelProvider.Factory {

    @Suppress("UNCHECKED_CAST")
    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        var creator: Provider<out ViewModel>? = creators[modelClass]
        if (creator == null) {
            for ((key, value) in creators) {
                if (modelClass.isAssignableFrom(key)) {
                    creator = value
                    break
                }
            }
        }
        if (creator == null) {
            throw IllegalArgumentException("unknown model class " + modelClass)
        }
        try {
            return creator.get() as T
        } catch (e: Exception) {
            throw RuntimeException(e)
        }

    }
}

But the project doesn't compile :( I have this error (Map<...> cannot be provided without an @Provides-annotated method.):

Using Kotlin incremental compilation
:mobile:transformDataBindingWithDataBindingMergeArtifactsForDebug UP-TO-DATE
:mobile:kaptDebugKotlin
e: /Users/jaumard/LISAProjects/LISA/mobile/build/tmp/kapt3/stubs/debug/com/mylisabox/lisa/dagger/components/ApplicationComponent.java:6: error: [com.mylisabox.lisa.dagger.components.ActivityComponent.inject(com.mylisabox.lisa.common.BaseActivity)] java.util.Map<java.lang.Class<? extends android.arch.lifecycle.ViewModel>,javax.inject.Provider<android.arch.lifecycle.ViewModel>> cannot be provided without an @Provides-annotated method.
e: 

e: public abstract interface ApplicationComponent {
e:                 ^
e:       java.util.Map<java.lang.Class<? extends android.arch.lifecycle.ViewModel>,javax.inject.Provider<android.arch.lifecycle.ViewModel>> is injected at
e:           com.mylisabox.lisa.dagger.ViewModelFactory.<init>(creators)
e:       com.mylisabox.lisa.dagger.ViewModelFactory is injected at
e:           com.mylisabox.lisa.common.BaseActivity.factory
e:       com.mylisabox.lisa.common.BaseActivity is injected at
e:           com.mylisabox.lisa.dagger.components.ActivityComponent.inject(activity)
e: /Users/jaumard/LISAProjects/LISA/mobile/build/tmp/kapt3/stubs/debug/com/mylisabox/lisa/dagger/components/ActivityComponent.java:4: error: com.mylisabox.lisa.dagger.components.ActivityComponent scoped with @com.mylisabox.network.dagger.annotations.ActivityScope may not reference bindings with different scopes:
e: 

Any idea on how fix this ?

回答1:

So ok I found the issue, the problem was under my ViewModelModule I need to return ViewModel from my abstract methods not directly the type I want. It will become like this then :

@Module
abstract class ViewModelModule {
    @Binds
    @IntoMap
    @ViewModelKey(LoginViewModel::class)
    internal abstract fun bindLoginViewModel(viewModel: LoginViewModel): ViewModel

    @Binds
    @IntoMap
    @ViewModelKey(MainMenuViewModel::class)
    internal abstract fun bindSearchViewModel(viewModel: MainMenuViewModel): ViewModel

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

来源：https://stackoverflow.com/questions/46435424/kotlin-dagger-2-android-viewmodel-injection-error