片段中的 Listview 适配器给出空指针异常

Question

I made a listview in a fragment There is a null pointer exception for the adapter of the list view But the Arraylist and the adapter are not null.

Error: lvElevator cannot be null

The error is for the below line

lvElevator.adapter = EAdapter

Fragment Class

var EList=ArrayList<E1List>()

class EDetails: Fragment() {

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        EList.add(E1List(1))
        EList.add(E1List(2))
        var EAdapter = EleAdapter(EList)
        lvElevator.adapter = EAdapter
        return inflater.inflate(R.layout.fragment_elevators, container, false)

    }

    inner class EleAdapter : BaseAdapter {
        var EListAdapter = ArrayList<E1List>()

        constructor(EListAdapter: ArrayList<E1List>) : super() {
            this.EListAdapter = EListAdapter
        }

        override fun getView(position: Int, convertView: View?, parent: ViewGroup?): View {
            var myView = layoutInflater.inflate(R.layout.elevator_ticket, null)
            var myEle = EListAdapter[position]
            myView.tvEnum.text = myEle.elevatornum.toString()
            return myView
        }

        override fun getItem(position: Int): Any {
            return EListAdapter[position]
        }

        override fun getItemId(position: Int): Long {
            return position.toLong()
        }

        override fun getCount(): Int {
            return EListAdapter.size
        }

    }
}

Answer 1

You are trying to define lvElevator before fragment inflate the xml layout file. There is two way to fix it.

1) Use onViewCreated() method instead to load data into views. And use onCreateView method to just inflate the view only.

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    EList.add(E1List(1))
    EList.add(E1List(2))
    var EAdapter = EleAdapter(EList)
    lvElevator.adapter = EAdapter
}

2) Modify onCreateView() method like below.

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {

    // Define views manually..
    val view = inflater.inflate(R.layout.fragment_elevators, container, false)
    val lvElevator = view.findViewById<ListView>(R.id.lvElevator)

    EList.add(E1List(1))
    EList.add(E1List(2))
    var EAdapter = EleAdapter(EList)
    lvElevator.adapter = EAdapter
    return view
}

As an experienced developer, I would recommended to use the first way as that method will only come in scope after layout completely inflated.