Fragment IoC issue

1_FragmentIocIssue.kt

//region UserFragment module

class UserFragment(dataSource: UserDataSource) : Fragment()

interface UserDataSource {
    fun getUser(): User
}

//endregion UserFragment module

//region ParentFragment module, depends on the UserFragment module

class ParentFragment : Fragment() {

    private val fragmentFactory = FragmentFactoryImpl()

    override fun onCreate(savedInstanceState: Bundle?) {
        childFragmentManager.fragmentFactory = fragmentFactory
        super.onCreate(savedInstanceState)
    }

    // Call this method when you need to show UserFragment displaying current user's info
    private fun showCurrentUser() {
        childFragmentManager.commit {
            add(R.id.content, fragmentFactory.currentUserFragment())
        }
    }

    // Call this method when you need to show UserFragment displaying other user's info
    private fun showOtherUser(id: String) {
        childFragmentManager.commit {
            add(R.id.content, fragmentFactory.otherUserFragment(id = id))
        }
    }
}

internal class FragmentFactoryImpl : FragmentFactory() {
    override fun instantiate(classLoader: ClassLoader, className: String): Fragment =
        when (loadFragmentClass(classLoader, className)) {
            UserFragment::class.java ->
                // We need somehow distinguish between current and other users here,
                // and call either currentUserFragment() or otherUserFragment().
                // In case of Other User we also need an id.
                TODO()

            else -> super.instantiate(classLoader, className)
        }

    fun currentUserFragment(): UserFragment = UserFragment(CurrentUserDataSource())

    fun otherUserFragment(id: String): UserFragment = UserFragment(OtherUserDataSource(id = id))
}

internal class CurrentUserDataSource : UserDataSource {
    override fun getUser(): User = TODO() // Load current user
}

internal class OtherUserDataSource(id: String) : UserDataSource {
    override fun getUser(): User = TODO() // Load other user
}

//endregion ParentFragment module

2_FragmentIocWorkaround.kt

//region UserFragment module

class UserFragment(dataSourceFactory: (Mode) -> UserDataSource) : Fragment() {

    private val mode by lazy { requireArguments().getParcelable<Mode>(KEY_MODE)!! }
    private val dataSource by lazy { dataSourceFactory(mode) }

    companion object {
        private const val KEY_MODE = "MODE"

        operator fun invoke(mode: Mode, dataSourceFactory: (Mode) -> UserDataSource): UserFragment =
            UserFragment(dataSourceFactory).apply {
                arguments = bundleOf(KEY_MODE to mode)
            }
    }

    // This makes the UserFragment aware of the Mode in one dimension - Current/Other.
    // It also makes impossible to reuse the UserFragment in a different context,
    // supplying the UserDataSource based on an another dimension (e.g. based on gender, relationship with current user, etc.).
    // You will need to add more variants here.
    sealed class Mode : Parcelable {
        @Parcelize
        object Current : Mode()

        @Parcelize
        data class Other(val id: String) : Mode()
    }
}

interface UserDataSource {
    fun getUser(): User
}

//endregion UserFragment module

//region ParentFragment module, depends on the UserFragment module

class ParentFragment : Fragment() {

    private val fragmentFactory = FragmentFactoryImpl()

    override fun onCreate(savedInstanceState: Bundle?) {
        childFragmentManager.fragmentFactory = fragmentFactory
        super.onCreate(savedInstanceState)
    }

    // Call this method when you need to show UserFragment displaying current user's info
    private fun showCurrentUser() {
        childFragmentManager.commit {
            add(R.id.content, fragmentFactory.currentUserFragment())
        }
    }

    // Call this method when you need to show UserFragment displaying other user's info
    private fun showOtherUser(id: String) {
        childFragmentManager.commit {
            add(R.id.content, fragmentFactory.otherUserFragment(id = id))
        }
    }
}

internal class FragmentFactoryImpl : FragmentFactory() {
    override fun instantiate(classLoader: ClassLoader, className: String): Fragment =
        when (loadFragmentClass(classLoader, className)) {
            UserFragment::class.java -> UserFragment(::userDataSource)
            else -> super.instantiate(classLoader, className)
        }

    fun currentUserFragment(): UserFragment = UserFragment(UserFragment.Mode.Current, ::userDataSource)

    fun otherUserFragment(id: String): UserFragment = UserFragment(UserFragment.Mode.Other(id), ::userDataSource)

    private fun userDataSource(mode: UserFragment.Mode): UserDataSource =
        when (mode) {
            is UserFragment.Mode.Current -> CurrentUserDataSource()
            is UserFragment.Mode.Other -> OtherUserDataSource(id = mode.id)
        }
}

internal class CurrentUserDataSource : UserDataSource {
    override fun getUser(): User = TODO() // Load current user
}

internal class OtherUserDataSource(id: String) : UserDataSource {
    override fun getUser(): User = TODO() // Load other user
}

//endregion ParentFragment module

3_FragmentIocImaginarySolution.kt

class ParentFragment : Fragment() {

    private val fragmentFactory = FragmentFactoryImpl()

    override fun onCreate(savedInstanceState: Bundle?) {
        childFragmentManager.fragmentFactory = fragmentFactory
        super.onCreate(savedInstanceState)
    }

    // Call this method when you need to show UserFragment displaying current user's info
    private fun showCurrentUser() {
        childFragmentManager.commit {
            add(R.id.content, fragmentFactory.configurationBundle(FragmentFactoryImpl.Configuration.CurrentUser))
        }
    }

    // Call this method when you need to show UserFragment displaying other user's info
    private fun showOtherUser(id: String) {
        childFragmentManager.commit {
            add(R.id.content, fragmentFactory.configurationBundle(FragmentFactoryImpl.Configuration.OtherUser(id = id)))
        }
    }
}

internal class FragmentFactoryImpl : FragmentFactory() {
    override fun instantiate(bundle: Bundle): Fragment =
        when (val configuration = bundle.getParcelable<Configuration>(KEY_CONFIGURATION)!!) {
            is Configuration.CurrentUser -> currentUserFragment()
            is Configuration.OtherUser -> otherUserFragment(id = configuration.id)
        }

    fun configurationBundle(configuration: Configuration): Bundle = 
        bundleOf(KEY_CONFIGURATION to configuration)
    
    private fun currentUserFragment(): UserFragment = UserFragment(CurrentUserDataSource())

    private fun otherUserFragment(id: String): UserFragment = UserFragment(OtherUserDataSource(id = id))
    
    private companion object {
        private const val KEY_CONFIGURATION = "CONFIGURATION"
    }
    
    sealed class Configuration : Parcelable {
        @Parcelize
        object CurrentUser : Configuration()

        @Parcelize
        data class OtherUser(val id: String): Configuration()
    }
}