gistfile1.txt

open class LinearLayoutManagerExt @JvmOverloads constructor (
        val name : String,
        val fragment: Fragment,
        val adapter : RecyclerView.Adapter<out RecyclerView.ViewHolder>,
        attrs : AttributeSet? = null,
        defStyleAttr : Int = 0,
        defStyleRes : Int = 0
) : LinearLayoutManager(fragment.requireContext(),attrs,defStyleAttr,defStyleRes){

    protected var savedState : SavedState? = fragment.arguments?.getParcelable<SavedState?>(name)

    protected val lifecycleObserver = object  : LifecycleEventObserver {
        override fun onStateChanged(source: LifecycleOwner, event: Lifecycle.Event) {
            when (event) {
                Lifecycle.Event.ON_PAUSE -> {
                    val parc = onSaveInstanceState()
                    if (fragment.arguments == null) {
                        fragment.arguments = Bundle()
                    }
                    fragment.arguments?.putParcelable(name, parc)
                    fragment.lifecycle.removeObserver(this)
                }
            }
        }

    }

    protected val adapterDataObserver = object : RecyclerView.AdapterDataObserver() {

        override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
            if(savedState != null && itemCount > 0){
                onRestoreInstanceState(savedState)
                savedState = null
            }
            if(itemCount > 0){
                adapter.unregisterAdapterDataObserver(this)
            }
        }
    }

    init {
        fragment.lifecycle.addObserver(lifecycleObserver)
        adapter.registerAdapterDataObserver(adapterDataObserver )
    }

    override fun onDetachedFromWindow(view: RecyclerView?, recycler: RecyclerView.Recycler?) {
        super.onDetachedFromWindow(view, recycler)
        try{
            adapter.unregisterAdapterDataObserver(adapterDataObserver )
        } catch (_ : Exception){}
    }

}