我一直在尝试为Android中的布局元素设置新的自定义ArrayAdapter（我已经做了很多次了），但是每当我开始活动时，似乎在代码中的某个地方出现了空对象引用错误。
我检查了每个细节，似乎没有什么不寻常的。
我的CustomAdapter文件（CustomAdapterRangliste）：
package ba.unsa.etf.rma.klase;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import java.util.ArrayList;
import ba.unsa.etf.rma.R;
public class CustomAdapterRangliste extends ArrayAdapter<RangLista> {
private Context mContext;
private int resources;
private ArrayList<RangLista> rang;
public CustomAdapterRangliste(Context context, int res, ArrayList<RangLista> rang) {
super(context, res, rang);
mContext = context;
resources = res;
this.rang = rang;
}
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = LayoutInflater.from(mContext);
convertView = inflater.inflate(R.layout.rangliste, parent, false);
//View view = inflater.inflate(R.layout.activity_igraj_kviz_akt, null);
TextView textView = (TextView) convertView.findViewById(R.id.etRangliste);
final RangLista rangIgraca = rang.get(position);
textView.setText(rangIgraca.toString());
return convertView;
}
}
布局元素（rangliste.xml）
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/etRangliste"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="8dp"
android:layout_marginBottom="696dp"
android:text="TextView"
android:textSize="24sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
我用于初始化和绑定CustomAdapter的代码（在实现该片段的活动中）：
final ListView rangLista = (ListView) findViewById(R.id.lvRanglista);
final ArrayList<RangLista> ranking = new ArrayList<>();
final CustomAdapterRangliste rangAdapter = new CustomAdapterRangliste(this, R.layout.rangliste, ranking);
rangLista.setAdapter(rangAdapter);
具有ListView元素的布局文件（fragment_ranglista.xml）：
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".fragmenti.RanglistaFrag">
<!-- TODO: Update blank fragment layout -->
<ListView
android:id="@+id/lvRanglista"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#4FD80000"
android:scrollbars="vertical" />
</FrameLayout>
片段文件：
package ba.unsa.etf.rma.fragmenti;
import android.content.Context;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import ba.unsa.etf.rma.R;
/**
* A simple {@link Fragment} subclass.
* Activities that contain this fragment must implement the
* {@link RanglistaFrag.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {@link RanglistaFrag#newInstance} factory method to
* create an instance of this fragment.
*/
public class RanglistaFrag extends Fragment {
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
public RanglistaFrag.OnFragmentInteractionListener2 mListener;
public void postaviListener (RanglistaFrag.OnFragmentInteractionListener2 mListener)
{
this.mListener=mListener;
}
public RanglistaFrag() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment ba.unsa.etf.rma.fragmenti.RanglistaFrag.
*/
// TODO: Rename and change types and number of parameters
public static RanglistaFrag newInstance(String param1, String param2) {
RanglistaFrag fragment = new RanglistaFrag();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_ranglista, container, false);
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
/* if (mListener != null) {
mListener.onFragmentInteraction(uri);
}*/
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
/*if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}*/
}
@Override
public void onDetach() {
super.onDetach();
// mListener = null;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener2 {
// TODO: Update argument type and name
public void azuriranjeRangliste();
}
}
我不知道自己在做什么错，没有类似的问题对我有帮助，我检查了遗漏的行，但没有成功
最佳答案
该错误意味着，当您调用此rangLista.setAdapter(rangAdapter);时，变量rangLista为null。这可以通过多种方式发生，但是我首先要检查的是您是否在夸大正确的布局，因为findViewById(R.id.lvRanglista);行很可能返回null。
检查布局文件是否包含列表视图，该列表视图具有您在findViewById中使用的ID。