Why does fragmentmanager get destroyed after config change?

Question

Android

There is a fragment that is attached to Activuty as follows.

override fun onAttach(context: Context) {
        super.onAttach(context)
        try{
            activityContract = context as IActivity
        }catch (e:ClassCastException){
            throw ClassCastException(context.toString() + "Активити должна реализовывать интерфейс IActivityView")
        }
    }

IActivity is the interface that my activity implements. It contains methods for managing the Progress Bar element and a method for creating an ErrorDialogFragment.
By reference activityContract I call the methods of Activity. They all work, but after rotating the screen in one method that uses the FragmentManager, an exception is thrown:

illegalstateexception: fragmentmanager has been destroyed

I don't understand why this is happening... In the onCreate() method, the Activity() fragmentManager is initialized.

lateinit var fragmentManager:FragmentManager
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_search)
        fragmentManager = supportFragmentManager
}

Answer 1

The problem arose due to the fact that I did not unbind the fragment from the Activity when changing the screen configuration.
In the fragment's onDestroy() method, you need to nullify the reference to the Activity.