为什么我在使用微调器的片段中不断收到 null 参考错误？

Question

I am trying to put a spinner in my android fragment, but when ever I open the fragment, I get a java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)' on a null object reference. I tried putting the same code in main activity, and it works. Is there something wrong with a context?

 class AlarmLabelDialogFragment: DialogFragment() {

    val alarmRepository = AlarmRepository.get()

    lateinit var alarm: Alarm
    private val TAG = "tag1"



    override fun onCreateView(

        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        dialog?.window?.setBackgroundDrawable(R.drawable.ic_launcher_background.toDrawable())
            var rootView: View = inflater.inflate(R.layout.alarm_label_dialog_fragment, container, false)


        val tonesArray = arrayOf("Geese", "Thunder")
        ArrayAdapter.createFromResource(
            requireActivity().applicationContext,
            R.array.tonesArray,
            android.R.layout.simple_spinner_item
        ).also { adapter ->            
            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item)
            tonePickerDropDown.adapter = adapter
        }
        //val toneArrayAdapter =  ArrayAdapter(rootView.context, android.R.layout.simple_spinner_item, tonesArray)
        //tonePickerDropDown.adapter = toneArrayAdapter
        val bundle = arguments
        val id = bundle!!.get("id")
        alarm = alarmRepository.getAlarm(id.toString().toLong())

        rootView.alarmLabelEditTextTextMultiLine.setText(alarm.alarmLabel)
        rootView.alarmTimeFragmentLabel.setText(alarm.hour + ":" + alarm.minute)



        rootView.cancelButton.setOnClickListener {
        dismiss()
        }

        rootView.clearButton.setOnClickListener {
            rootView.alarmLabelEditTextTextMultiLine.setText("")
        }

        tonePickerDropDown.setOnItemSelectedListener(object : AdapterView.OnItemSelectedListener {
            override fun onItemSelected(parent: AdapterView<*>?, view: View?, position: Int, id: Long) {
                Log.i(
                    TAG,
                    "SELECTED TONE = $position "
                )
            } // to close the onItemSelected

            override fun onNothingSelected(parent: AdapterView<*>?) {}
        })

        rootView.confirmButton.setOnClickListener {

            if (alarmLabelEditTextTextMultiLine.text.toString() == ""){
                alarm.alarmLabel = "Label"

            }
            else {
                alarm.alarmLabel = alarmLabelEditTextTextMultiLine.text.toString()
            }

            alarmRepository.updateAlarm(alarm)
            (activity as MainActivity).alarmListRefresh()
            (activity as MainActivity).rvSet()
            dismiss()


        }

        //rootView.alarmLabelEditTextTextMultiLine.setSelection()


        return rootView
    }





}

Answer 1

tonePickerDropDown is null, debug and check out why? You might have to do rootView.tonePickerDropDown instead – Nongthonbam Tonthoi 2 days ago

2 days ago Nongthonbam Tonthoi's solution worked. thanks so much. you are a genius. Please submit it as an answer so I can accept it.