Dagger 2 Named cannot be provided without a @Provides method

问题

Trying to grok Dagger 2 and having an issue with named providers. I have a simple setup as follows:

// Module
@Module
class AppModule(private val app: App) {
    @Provides @AppScope fun providesApp() = app

    @Provides @AppScope fun provideSharedPreferences(app: App) = PreferenceManager.getDefaultSharedPreferences(app)

    @Provides @AppScope @Named("Uri1") fun providesUri1() = Uri.Builder().scheme("https").authority("authory1").build()

    @Provides @AppScope @Named("Uri2") fun providesUri2() = Uri.Builder().scheme("https").authority("authory2").build()
}

// Component
@AppScope
@Component(modules = arrayOf(AppModule::class))
interface AppComponent {
    fun inject(target: MainActivity)
}

// MainActivity
@Inject @AppScope lateinit var preferences: SharedPreferences
@Inject @AppScope @Named("Uri1") lateinit var uri1: Uri
@Inject @AppScope @Named("Uri2") lateinit var uri2: Uri

When rebuilding my project I am given:

Error:Gradle: android.net.Uri cannot be provided without an @Provides- or @Produces-annotated method.

I don't understand why adding the Named qualifier doesn't work for me here. If I remove these I can get an instance of SharedPreferences without issue.

Any insight into what I'm doing wrong would be appreciated!

EDIT:

Changes per suggestions with the same results as above.

// New module
@Module
class AppModule(private val app: App) {
    @Provides @AppScope fun providesApp() = app

    @Provides @AppScope fun provideSharedPreferences(app: App) = PreferenceManager.getDefaultSharedPreferences(app)

    @Provides @AppScope @Tag("Uri1") fun providesUri1(): Uri = Uri.Builder().scheme("https").authority("authority1").build()

    @Provides @AppScope @Tag("Uri2") fun providesUri2(): Uri = Uri.Builder().scheme("https").authority("authority2").build()
}

// Tag annotation
@Qualifier
@Retention(AnnotationRetention.RUNTIME)
annotation class Tag(val tag: String = "")

// MainActivity
@Inject @AppScope lateinit var preferences: SharedPreferences
@Inject @AppScope @Tag("Uri1") lateinit var uri1: Uri
@Inject @AppScope @Tag("Uri2") lateinit var uri2: Uri

Project Repo @ Github

回答1:

I think I found the problem (at least I checked out your project and it generated dagger classes correctly). If you need to inject fields annotated with @Named or some @Qualifier annotation you have to use this kind of syntax:

class MainActivity : AppCompatActivity() {
    @Inject lateinit var preferences: SharedPreferences
    @Inject @field:[Named ("Uri1")] lateinit var uri1: Uri // for @Named annotation or...
    @Inject @field:Uri2 lateinit var uri2: Uri // ...for @Qualifier annotation

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        app().component.inject(this)

        println(uri1)
        println(uri2)
    }
}

Notice how @Named / qualifier annotation goes inside @field: (without @ itself).

Idea borrowed from this repo.

来源：https://stackoverflow.com/questions/36199796/dagger-2-named-cannot-be-provided-without-a-provides-method

标签

android

dependency-injection

kotlin

dagger-2