Fragment lifecycle is slightly different from activity, most notably you have to break down view initialization because it has separate lifecycle (unlike activity it can be detached and undergo view destruction while leaving fragment itself intact). For that you should use onViewCreated method and implement onDestroyView to clear view references.

Best practice inside fragment to obtain context is to use requireContext() then you can proceed to pull applicationContext from it if needed.

Also fragment doesn’t have setContentView method. You have to either override onCreateView method or if you’re using static layout you can use Fragment (int contentLayoutId) constructor instead:

class HomeFragment : Fragment(R.layout.activity_main) {
    private var alphaAdapters: AlphaAdapters? = null
    private var charItem: ArrayList<CharItem>? = null

    private var recyclerView: RecyclerView? = null
    private var gridLayoutManager: GridLayoutManager? = null

    // initialize adapter in onCreate, it's unaffected by views state
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        charItem = ArrayList()
        charItem = setAlphas()
        alphaAdapters = AlphaAdapters(requireContext(), charItem!!)
    }

    // initialize recyclerView and layout manager
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        gridLayoutManager = GridLayoutManager(requireContext(), 2, LinearLayoutManager.VERTICAL, false)
        recyclerView = view.findViewById(R.id.recycler_view_item).also {
            it.layoutManager = gridLayoutManager
            it.setHasFixedSize(true)
            it.adapter = alphaAdapters
        }
   }

    // release recyclerView and layout manager
   override fun onDestroyView() {
       super.onDestroyView()
       recyclerView?.adapter = null
       recyclerView = null
       gridLayoutManager = null
   }

   private fun setAlphas(): ArrayList<CharItem> {
       // (....)
   }
}

I am new with using GridLayoutManager and need some help with its initializing. I created test version of recyclerview with cardview and it worked perfectly when my code was placed in mainactivity. But now when I copied it to main project to my HomeFragment there was shown errors with GridLayout manager initializing.

my code in HomeFragment:

class HomeFragment : Fragment() {
private var recyclerView: RecyclerView? = null
private var charItem: ArrayList<CharItem>? = null
private var gridLayoutManager: GridLayoutManager? = null
private var alphaAdapters: AlphaAdapters? = null

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    applicationContext
    recyclerView = findViewById(R.id.recycler_view_item)
    gridLayoutManager =
        GridLayoutManager(**applicationContext**, 2, LinearLayoutManager.VERTICAL, false)
    recyclerView?.layoutManager = gridLayoutManager
    recyclerView?.setHasFixedSize(true)
    charItem = ArrayList()
    charItem = setAlphas()
    alphaAdapters = AlphaAdapters(**applicationContext,** charItem!!)
    recyclerView?.adapter = alphaAdapters

}

private fun setAlphas(): ArrayList<CharItem> {

    var arrayList: ArrayList<CharItem> = ArrayList()

    arrayList.add(CharItem(R.drawable.image_3__2_, R.drawable.ic_nail,"Nail 
услуги")).....

}

Problem is in application context

So the problem is in HomeFragment code especially with ApplicationContext in GridLayoutManager. What is the solution? Is there anything which can help me?