Android ListView.setAdapter(android.widget.ListAdapter)' on a null object reference

Question

我创建了一个Android应用程序，我尝试有一个自定义的列表视图。所有数据都来自我的休息服务，我已经检查了这些值是否在我的列表中。但是当我设置适配器时，出现此错误：

07-29 15:56:00.357 6552-6552/ejplanningandroid.ejplanningandroid W/System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
07-29 15:56:00.357 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at ejplanningandroid.ejplanningandroid.PlanningFragment.onCreateView(PlanningFragment.java:68)
07-29 15:56:00.357 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
07-29 15:56:00.357 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
07-29 15:56:00.358 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
07-29 15:56:00.358 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
07-29 15:56:00.358 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
07-29 15:56:00.358 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
07-29 15:56:00.358 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at android.os.Handler.handleCallback(Handler.java:739)
07-29 15:56:00.358 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:95)
07-29 15:56:00.358 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at android.os.Looper.loop(Looper.java:148)
07-29 15:56:00.358 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:5417)
07-29 15:56:00.358 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at java.lang.reflect.Method.invoke(Native Method)
07-29 15:56:00.358 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
07-29 15:56:00.358 6552-6552/ejplanningandroid.ejplanningandroid W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

但是我初始化我的适配器有一个我的片段：

规划片段：

public class PlanningFragment extends Fragment {
private ListView mListView;
private View view;
private List<Planning> listPlanning = new ArrayList<Planning>();
@Override
public View onCreateView(LayoutInflater inflater, @Nullable final ViewGroup container, @Nullable Bundle savedInstanceState) {
view = inflater.inflate(R.layout.menu_fragment, container, false);
mListView = (ListView) view.findViewById(R.id.listViewPlanning);
String path = "http://192.168.128.13:8081/EJPlanningRest-Colart/planning/moniteur?login="+
((MainActivity) getActivity()).getUtilisateur().getLogin()
+"&password="+((MainActivity) getActivity()).getUtilisateur().getMotDepasse();
try {
JsonArrayTask JsonArray = (JsonArrayTask) new JsonArrayTask().execute(path);
if(JsonArray.get() != null) {
for (int i = 0; i < JsonArray.get().length(); i++) {
Log.i("ICI",""+JsonArray.get().length());
Planning planning = new Planning();
planning.setDate(JsonArray.get().getJSONObject(i).getString("dateEvenement"));
planning.setType(JsonArray.get().getJSONObject(i).getString("Type"));
JSONObject json_data = JsonArray.get().getJSONObject(i);
JSONArray jsonArrayActivitePlanning = json_data.getJSONArray("ActivitePlannings");
JSONArray jsonArrayUtilisateurPlannings = json_data.getJSONArray("UtilisateurPlannings");
JSONObject Groupe =json_data.getJSONObject("Groupe");
planning.setNomGroupe(Groupe.getString("NomGroupe"));
if(jsonArrayActivitePlanning != null || jsonArrayUtilisateurPlannings != null ) {
List<String> NomActivite = new ArrayList<String>();
List<String> NomUtilisateur = new ArrayList<String>();
for (int j = 0; j < jsonArrayActivitePlanning.length(); j++) {
NomActivite.add(jsonArrayActivitePlanning.getJSONObject(j).getString("nomActivite"));
}
for (int j = 0; j < jsonArrayUtilisateurPlannings.length(); j++) {
NomUtilisateur.add(jsonArrayUtilisateurPlannings.getJSONObject(j).getString("nomUtilisateur"));
}
planning.setNomActivite(NomActivite);
planning.setUtilisateurs(NomUtilisateur);
}
listPlanning.add(planning);
}
Log.i("Count",""+listPlanning.size());
PlanningAdapter adapter = new PlanningAdapter(view.getContext(),listPlanning);
mListView.setAdapter(adapter);
}
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
} catch (JSONException e) {
e.printStackTrace();
}
return view;
}

规划视图持有人 ：

public class PlanningViewHolder {
public TextView Date;
public TextView NomGroupe;
public TextView Type;
public TextView NomActivite;
public TextView Utilisateur;
}

还有我的类，我在其中创建适配器。没有什么复杂的，但我不知道为什么我有一个空异常......

public class PlanningAdapter extends ArrayAdapter<Planning> {
public PlanningAdapter (Context context, List<Planning> plannings){
super(context, 0, plannings);
}
@Override
public View getView(int position, View view, ViewGroup parent) {
if(view == null){
view = LayoutInflater.from(getContext()).inflate(R.layout.rowplanning,parent, false);
}
PlanningViewHolder planningViewHolder = (PlanningViewHolder)view.getTag();
if(planningViewHolder==null){
planningViewHolder= new PlanningViewHolder();
planningViewHolder.Date = (TextView)view.findViewById(R.id.Date);
planningViewHolder.NomActivite =(TextView)view.findViewById(R.id.Activite);
planningViewHolder.NomGroupe = (TextView)view.findViewById(R.id.NomGroupe);
planningViewHolder.Type = (TextView)view.findViewById(R.id.Type);
planningViewHolder.Utilisateur = (TextView)view.findViewById(R.id.Utilisateur);
view.setTag(planningViewHolder);
}
Planning planning = getItem(position);
planningViewHolder.Type.setText(planning.getType());
planningViewHolder.NomGroupe.setText(planning.getNomGroupe());
String nomActivite = setStringFromArray(planning.getNomActivite());
planningViewHolder.NomActivite.setText(nomActivite);
planningViewHolder.Date.setText(planning.getDate().toString());
String nomUtilisateur =setStringFromArray(planning.getUtilisateurs());
planningViewHolder.Utilisateur.setText(nomUtilisateur);
return view;
}
public String setStringFromArray(List<String> Array ){
String result="";
for (String nomGroupePlanning : Array){
if(nomGroupePlanning !="") {
result += "-" + nomGroupePlanning;
}else{
result += nomGroupePlanning;
}
}
return result;
}
}

行规划 XML

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
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"
android:padding="10dp" >
<TextView
android:id="@+id/Date"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="@android:color/black"
android:layout_marginLeft="10dp"
android:textStyle="bold"
tools:text="Date" />
<TextView
android:id="@+id/NomGroupe"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="@android:color/black"
android:layout_below="@+id/Date"
android:layout_marginLeft="10dp"
android:textStyle="bold"
tools:text="Groupe" />
<TextView
android:id="@+id/Type"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="@android:color/black"
android:layout_below="@+id/NomGroupe"
android:layout_marginLeft="10dp"
android:textStyle="bold"
tools:text="Type" />
<TextView
android:id="@+id/Activite"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="@android:color/black"
android:layout_below="@+id/Type"
android:layout_marginLeft="10dp"
android:textStyle="bold"
tools:text="Activite"
/>
<TextView
android:id="@+id/Utilisateur"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="@android:color/black"
android:layout_below="@+id/Activite"
android:layout_marginLeft="10dp"
android:textStyle="bold"
tools:text="Utilisateur"
/>
</RelativeLayout>

片段规划 XML

<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ListView
android:id="@+id/listViewPlanning"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>

Answer 1

你已经写了

view = inflater.inflate(R.layout.menu_fragment, container, false);

但是您的布局名称(menu_fragment(与您在问题中指定的不同，即FRAGMENTPLANNING，将其更改为正确的XML名称，它应该可以工作。

Answer 2

将此 PlanningViewHolder planningViewHolder 对象设为私有字段，并使用从活动传递到适配器的上下文。

public View getView(int position, View view, ViewGroup parent) {
if(view == null){
LayoutInflater mInflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
view = mInflater.inflate(R.layout.rowplanning,parent, false);
planningViewHolder= new PlanningViewHolder();
planningViewHolder.Date = (TextView)view.findViewById(R.id.Date);
planningViewHolder.NomActivite =(TextView)view.findViewById(R.id.Activite);
planningViewHolder.NomGroupe = (TextView)view.findViewById(R.id.NomGroupe);
planningViewHolder.Type = (TextView)view.findViewById(R.id.Type);
planningViewHolder.Utilisateur = (TextView)view.findViewById(R.id.Utilisateur);
view.setTag(planningViewHolder);
} else {
planningViewHolder = (PlanningViewHolder)view.getTag();
}
Planning planning = getItem(position);
planningViewHolder.Type.setText(planning.getType());
planningViewHolder.NomGroupe.setText(planning.getNomGroupe());
String nomActivite = setStringFromArray(planning.getNomActivite());
planningViewHolder.NomActivite.setText(nomActivite);
planningViewHolder.Date.setText(planning.getDate().toString());
String nomUtilisateur =setStringFromArray(planning.getUtilisateurs());
planningViewHolder.Utilisateur.setText(nomUtilisateur);
return view;
}