Nullpointerexception When Trying to Access Views in a Kotlin Fragment

NullPointerException when trying to access views in a Kotlin fragment

Kotlin synthetic properties are not magic and work in a very simple way. When you access btn_K, it calls for getView().findViewById(R.id.btn_K).

The problem is that you are accessing it too soon. getView() returns null in onCreateView. Try doing it in the onViewCreated method:

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    btn_K.setOnClickListener { Log.d(TAG, "onViewCreated(): hello world"); }
}

How to detect cause of Null Pointer Exception on Android Extensions inside fragments

Android extensions plugin is deprecated and the official proposal is to use ViewBinding instead which provided compile time access to the views of an xml layout without the need to do viewFindById on each view you have.

This page here will provide you with the steps to set up your code to use view binding, make sure to check the code snippet on a fragment to clear the reference you have on the views

kotlin fragment error NullPointerException

Done. this my complete fix code with separate onCreateView and onViewCreate. thanks all

class FragBaru : Fragment() {

    private lateinit var rv: RecyclerView

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        return inflater.inflate(R.layout.mainex, container, false)
    }

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

        rv = view.findViewById(R.id.recycler_view)

        val groupAdapter = GroupAdapter<ViewHolder>().apply {
            spanCount = 2
        }

        rv.apply {
            layoutManager = GridLayoutManager(rootView.context, groupAdapter.spanCount).apply {
                spanSizeLookup = groupAdapter.spanSizeLookup
            }
            adapter = groupAdapter
        }

        var headerTab: ArrayList<mTop>
        headerTab = arguments?.getSerializable("headertab") as ArrayList<mTop>

        for (h in 0 until headerTab.size) {
            val header = headerTab.get(h).kategori

            ExpandableGroup(ExpandableHeaderItem(header), true).apply {

                for (c in 0 until headerTab[h].sub.size) {
                    val gambar = (headerTab[h].sub).get(c).gambar
                    val nama_menu = (headerTab[h].sub).get(c).nama_menu
                    add(Section(FancyItem(gambar, nama_menu)))
                }

                groupAdapter.add(this)
            }

        }
    }

    companion object {
        fun newInstance(headertab: ArrayList<mTop>): FragBaru {
            val f = FragBaru()

            val args = Bundle()
            args.putSerializable("headertab", headertab)

            f.setArguments(args)
            return f
        }
    }

}

Kotlin Fragment NullPointerException

You are doing asynchronous I/O directly in a fragment. Then you are trying to update the UI of the fragment when that work completes.

The problem is that sometimes your fragment will be destroyed before that work completes (e.g., the user pressed the BACK button). In that case, context will be null and context!! will be... bad.

The tactical fix is to only update the UI if you have a context:

activity?.let {
    userAdapter = UsersAdapter(it, mUsers as ArrayList<Users>, false)
    recyclerView.adapter = userAdapter
}

The better fix, by a fair margin, is to get this I/O out of the fragment entirely. If the user triggers a configuration change (rotates the screen, toggles dark mode, etc.), your new fragment will not be getting the I/O results from the original fragment. It would be better to move this I/O into a ViewModel that your fragment uses, where you make those results available via a LiveData or similar mechanism. Your fragment would observe the LiveData and apply the results. This not only fixes the crash, but it also handles configuration changes better.

Android View Binding in Thread error NullPointerException

You may find this easier if you ditch the !! getter and just use nullable types with local non-null variables as-needed. If you have a lot of places to use the binding inside the loop you could grab a non-null value of it at the start of the loop.

private fun updateHomeUI() {
    Thread {
        // this could also be while(true) since the calls just
        // inside will break out when it goes null
        while (_binding != null) {  // Stop the loop after onDestroyView sets this to null
            val binding = _binding ?: break
            val a = activity as? MainActivity ?: break
            
            
            // Lots of UI update like this:
            a.runOnUiThread { binding.tvName.text = str }
            
            ...
            Thread.sleep(1000)
        }
    }.start()
}

I'm not sure how your existing bind.tvName != null loop condition would ever return false without first failing the !! check. The views in the binding class are non-null by default (unless they don't exist in all layout permutations), so that would either be true, or would fail in the bind getter when _binding is null.

Kotlin Null Pointer Exception when trying to open Activity

Activity or Fragment may be destroyed before request is finished executing. You can check if activity is not null:

val a = activity
if (a != null) {
    recyclerAdapter = HomeRecyclerAdapter(a, displayList) 
    recyclerHome.adapter = recyclerAdapter
    recyclerHome.layoutManager = layoutManager
}

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