Features Separating

DynamicConfig.kt

class DynamicConfig {
    companion object {
        // Here could be your feature toggle request
        var isTheFeatureAvailable = true
        var isOtherFeatureAvailable = false
    }
}

Featured.kt

interface Featured {
    fun doOnActivityCreated(action: (savedInstanceState: Bundle?) -> Unit)
    fun doOnActivityResult(action: (requestCode: Int, resultCode: Int, 
                                    data: Intent?) -> Unit)
}

FeatureFragment.kt

abstract class FeatureFragment : Fragment(), Featured {
    private var onActivityCreatedAction: MutableList<((savedInstanceState: Bundle?)
    -> Unit)>? = mutableListOf()
    
    private var onActivityResultAction: MutableList<((
        requestCode: Int, resultCode: Int, data: Intent?
    ) -> Unit)>? = mutableListOf()

    override fun doOnActivityCreated(action: (savedInstanceState: Bundle?) -> Unit) {
        onActivityCreatedAction?.add(action)
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        onActivityCreatedAction?.forEach { 
            it.invoke(savedInstanceState) 
        }
    }

    override fun doOnActivityResult(action: (requestCode: Int, resultCode: Int, 
                                             data: Intent?) -> Unit) {
        onActivityResultAction?.add(action)
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        onActivityResultAction?.forEach { 
            it.invoke(requestCode, resultCode, data) 
        }
    }
}

MainFragment.kt

class MainFragment : Fragment() {
    private var theFeature: TheFeature? = null
    private val viewModel: MainFragmentViewModel by viewModels()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        if (DynamicConfig.isTheFeatureAvailable) 
            theFeature = TheFeature(viewModel, this)
    }

    private fun someFunctionWhereTheFeatureMethodIsUsed(){
        // ...
        theFeature?.featureActions()
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        theFeature?.onActivityCreated(savedInstanceState)
    }

}

MainFragmentAdvanced.kt

class MainFragmentAdvanced : FeatureFragment() {
    private var theFeature: TheFinalFeature<MainFragmentAdvanced>? = null
}

TheFeature.kt

class TheFeature(private val viewModel: MainFragmentViewModel, 
                 private val fragment: Fragment) {
    fun featureActions() {
        // Some actions in the feature
        viewModel.doSomeActions()
    }

    fun onActivityCreated(savedInstanceState: Bundle?) {
        Toast.makeText(fragment.requireContext(), "Some feature text", 
                       Toast.LENGTH_LONG).show()
    }
}

TheFinalFeature.kt

class TheFinalFeature<T>(
    private val viewModel: ViewModel,
    private val fragment: T
) where T : Fragment, T : Featured {

    init {
        fragment.doOnActivityCreated(::onActivityCreated)
        fragment.doOnActivityResult(::onActivityResult)
    }

    private fun onActivityCreated(savedInstanceState: Bundle?) {
        //...
    }

    private fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        //...
    }
}

TheUnfinishedFeature.kt

class TheUnfinishedFeature(private val viewModel: ViewModel, 
                           private val fragment: Fragment) {
    init {
        fragment.onActivityCreated = onActivityCreated // How to do it?
    }
}