lateinit property adapter has not been initialized in Kotlin4Android

Question

I have created RecyclerView in fragment inside activity, all are working good but when i do notifyDataSetChanged() to adapter from activity through interface,I got an error "lateinit property adapter has not been initialized" but I have already initialized adapter

    class BuildingListFragment : Fragment(), MainActivity.EditInterface {


    lateinit var adapter: BuildingListAdapter

    private var mListener: OnFragmentInteractionListener? = null

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

    override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        // Inflate the layout for this fragment
        return inflater!!.inflate(R.layout.fragment_building_list, container, false)
    }

    override fun onViewCreated(view: View?, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        val buildingList = ArrayList<BuildingDetailModel>()

        val alphaList = arrayOf("A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K",
                "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "z")
        for (i in alphaList.indices) {

            val building = BuildingDetailModel()
            building.buildingName = alphaList[i] + " Building"
            buildingList.add(building)

        }

        //initialize adapter
        adapter = BuildingListAdapter(buildingList)
        // RV_Building_List.layoutManager = LinearLayoutManager(context, LinearLayout.VERTICAL, false)
        RV_Building_List.adapter = adapter

        RV_Building_List.layoutManager = object : LinearLayoutManager(activity, LinearLayoutManager.VERTICAL, false) {
            override fun onLayoutChildren(recycler: RecyclerView.Recycler?, state: RecyclerView.State) {
                super.onLayoutChildren(recycler, state)
                //TODO if the items are filtered, considered hiding the fast scroller here
                val firstVisibleItemPosition = findFirstVisibleItemPosition()
                if (firstVisibleItemPosition != 0) {
                    // this avoids trying to handle un-needed calls
                    if (firstVisibleItemPosition == -1)
                    //not initialized, or no items shown, so hide fast-scroller
                    {
                        fastscroller.visibility = View.GONE
                    }
                    return
                }
                val lastVisibleItemPosition = findLastVisibleItemPosition()
                val itemsShown = lastVisibleItemPosition - firstVisibleItemPosition + 1
                //if all items are shown, hide the fast-scroller
                fastscroller.visibility = if (adapter.itemCount > itemsShown) View.VISIBLE else View.GONE
            }
        }
        fastscroller.setRecyclerView(RV_Building_List)
        fastscroller.setViewsToUse(R.layout.recycler_view_fast_scroller__fast_scroller, R.id.fastscroller_bubble, R.id.fastscroller_handle)

    }

    override fun editClickFromMainActivity() {
        // TODO("not implemented") //To change body of created functions use File | Settings | File Templates.

        //at this line error  is lateinit property adapter has not been initialized
        if (adapter.getIsSelected()) adapter.setIsSelected(false) else adapter.setIsSelected(true)
    }

    override fun onDetach() {
        super.onDetach()
        mListener = null
    }

    override fun onResume() {
        super.onResume()

    }

    interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        fun onFragmentInteraction(uri: Uri)
    }

    companion object {

        // TODO: Rename and change types and number of parameters
        fun newInstance(): BuildingListFragment {
            val fragment = BuildingListFragment()
            return fragment
        }
    }
}

My mainActivity

    class MainActivity : AppCompatActivity() {

    private val mOnNavigationItemSelectedListener =
            BottomNavigationView.OnNavigationItemSelectedListener { item ->
                when (item.itemId) {
                    R.id.navigation_list -> {
                        val fragment = BuildingListFragment.Companion.newInstance();
                        addFragment(fragment, R.anim.slide_re_in, R.anim.slide_re_out)
                        return@OnNavigationItemSelectedListener true
                    }
                    R.id.navigation_map -> {
                        val fragment = BuildingMapFragment.Companion.newInstance();
                        addFragment(fragment, R.anim.slide_in, R.anim.slide_out)
                        return@OnNavigationItemSelectedListener true
                    }
                }
                false
            }

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

        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener)

        val fragment = BuildingListFragment.Companion.newInstance()
        addFragment(fragment, R.anim.slide_re_in, R.anim.slide_re_out)

        iv_Add.setOnClickListener {
            var intent = Intent(this, AddBuildingMapsActivity::class.java)
            startActivity(intent)
        }
        iv_edit.setOnClickListener {
            (BuildingListFragment.newInstance() as EditInterface).editClickFromMainActivity()
        }
    }


    /**
     * add/replace fragment in container [framelayout]
     */
    private fun addFragment(fragment: Fragment, slide_re_in: Int, slide_re_out: Int) {

        supportFragmentManager
                .beginTransaction()
                .setCustomAnimations(slide_re_in, slide_re_out)
                .replace(R.id.fragmentContainer, fragment, null)//fragment.javaClass.getSimpleName()
                .addToBackStack(null)//fragment.javaClass.getSimpleName()
                .commit()
    }

    override fun onBackPressed() {
        super.onBackPressed()
        Log.e("TAG", "TAG")
    }

    interface EditInterface {
        fun editClickFromMainActivity()
    }
}

please help me to solve this issue thanks..

Answer 1

Your problem is that you're creating a new instance of the fragment when the click handler is being called in the main activity line

(BuildingListFragment.newInstance() as EditInterface).editClickFromMainActivity()

You will need to call the method on the actual fragment instance that's currently on screen. There's various ways of getting around this but I think the safest path for now is doing something like

iv_edit.setOnClickListener {
    val fragment = supportFragmentManager.findFragmentByTag(FRAGMENT_TAG) as? BuildingListFragment
    fragment?.editClickFromMainActivity()
}

though this will mean that you must also use the same FRAGMENT_TAG in addFragment on the .replace(R.id.fragmentContainer, fragment, null) line (FRAGMENT_TAG instead of null)