只要有活动，Android Dagger 2 就会保持片段活着

Question

I have activity with bottom bar, that switches two fragments galleryFrament and profilefragment , that are injected into MainActivity :

class MainActivity : DaggerAppCompatActivity(), MainContract.View {

@Inject
lateinit var galleryFragment: GalleryFragment

@Inject
lateinit var profileFragment: ProfileFragment

I switch between them in this way:

val transaction = fragmentManager.beginTransaction()
transaction.replace(frameId, fragment)
transaction.commit()

Module that provides MainActivity , with Scope @ActivityScoped :

  @Module
  abstract class ActivityBindingModule {

    @ActivityScoped
    @ContributesAndroidInjector(modules = arrayOf(MainModule::class, GalleryModule::class, ProfileModule::class))
    internal abstract fun mainActivity(): MainActivity

Module that provides GalleryFragment :

  @Module
internal abstract class GalleryModule {

    @FragmentScoped
    @ContributesAndroidInjector
    abstract fun galleryFragment(): GalleryFragment

    @ActivityScoped
    @Binds
    abstract fun galleryPresenter(galleryPresenter: GalleryPresenter): GalleryContract.Presenter


    @Module
    companion object {
        @ActivityScoped
        @Provides
        @JvmStatic
        fun galleryAdapter(context: Context): GalleryAdapter {
            return GalleryAdapter(context);
        }
    }
}

And, finaly AppComponent :

@Singleton
@Component(modules = arrayOf(ImagesRepositoryModule::class,
        ApplicationModule::class,
        ActivityBindingModule::class,
        AndroidSupportInjectionModule::class,
        EventsModule::class))
interface AppComponent : AndroidInjector<MyApplication> {

GalleryFragment is provided with @FragmentScoped annotation from GaleryModule . I took aproach with annotatins @FragmentScoped and @ActivityScoped from google blueprints samples posted here: https://github.com/googlesamples/android-architecture][google-archutecture

The probem is: When I switch fragments, the new instance of GalleryFrament is created ( onCreate() called every time), but I want to use previously created instance of it. As I understand dagger scopes, GalleryFragment should be @ActivityScoped (to keep it alive as long as activity lives), but if I set it, @ContributesAndroidInjector produces Subcomponent with the same scope as its parent, and that is illegal.

Answer 1

If you want to have your fragment in your activity scope you mustn't create fragment subcomponent with @ContributesAndroidInjector so instead of

@FragmentScoped
@ContributesAndroidInjector
abstract fun galleryFragment(): GalleryFragment

try to move it in your companion like so

@Provides
@ActivityScoped
@JvmStatic
fun galleryFragment(): GalleryFragment = GalleryFragment.newInstance()

or remove it and from your GalleryFragment class

@ActivityScope
class GalleryFragment 
@Inject
constructor() : Fragment()

Though i wouldn't recommanded to do so, why would you want to have fragments matching your activity lifecycle?