Was ist die Ursache von NPE hier?

Question

Ich habe die Zeilennummern erwähnt, wo ich Laufzeitfehler Zeile 27,118,62 und 134 bekomme. Logcat ist auch da. Ich bekomme diese Fehler nach 30-35 Sekunden.

Warum erhalte ich es auf der Linie 27

Linie. 134: Listview Listview = (Listview) getView() findViewById (R.id.list4);

Die Warnung zeigt, dass NPE kann

public class Quizze extends android.support.v4.app.Fragment { //line 27 


JSONObject jsonobject; 
JSONArray jsonarray; 
String idno = " "; 



ArrayList<Details> details; 
LinearLayout layout; 
ArrayList<String> nameList; 
TextView textView; 

public Quizze() { 
} 



@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    SharedPreferences pref = getActivity().getPreferences(0); 
    pref.getString("url-address", "empty"); 

    new DownloadJSON().execute(); 
    return inflater.inflate(R.layout.quiz_result, container, false); 





} 


class DownloadJSON extends AsyncTask<Void, Void, Void> { //line 62 

    @Override 
    protected Void doInBackground(Void... params) { 


     SharedPreferences pref = getActivity().getPreferences(0); 
     String url = pref.getString("url-address", "empty"); 

     details = new ArrayList<>(); 

     jsonobject = JSONfunctions 
       .getJSONfromURL(url); 

     try { 
      // Locate the NodeList name 
      jsonarray = jsonobject.getJSONArray("results"); 
      for (int i = 0; i < jsonarray.length(); i++) { 
       jsonobject = jsonarray.getJSONObject(i); 
       Collections.reverse(details); 
       if (jsonobject.getString("resType").contains("Multiple Choice Questions")) { 
        { 
         Details detailAll = new Details(); 

         detailAll.setResType(jsonobject.optString("resType")); 
         detailAll.setName(jsonobject.optString("resName")); 
         detailAll.setUrl(jsonobject.optString("resLink")); 
         detailAll.setId(jsonobject.optInt("id")); 


         details.add(detailAll); 
         Collections.reverse(details); 
        } 
       } 

      } 


     } catch (JSONException e) { 
      Log.e("Error", "" + e.getMessage()); 
      e.printStackTrace(); 
     } 
     return null; 


} 

    @Override 
    protected void onPostExecute(Void args) { 


     nameList = new ArrayList<>(); 
     for (Details bean : details) { 
      nameList.add(bean.getResType()); 


      aero(details); //line 118 
     } 
    } 
} 

private void aero(List<Details> mList) { 


    for (Details bean : details) { 
     final String urlChar = bean.getUrl(); 

     idno = String.valueOf(bean.getId()); 

     if (bean.getResType().equals("Multiple Choice Questions")) 

     { 
      ListView listView = (ListView) getView().findViewById(R.id.list4);  //Line 134 

      CustomListViewAdapterMindMaps adapter = new CustomListViewAdapterMindMaps(getContext(), 
        R.layout.quiz_result, mList); 
      listView.setAdapter(adapter); 


      listView.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
       @Override 
       public void onItemClick(AdapterView<?> parent, View view, 
             int position, long id) { 


        Toast.makeText(getActivity(), 
          "Click ListItem Number " + idno, Toast.LENGTH_LONG); 


        Intent intent = new Intent(getContext(), Main_Activity_For_Quiz.class); 
        //add data to the Intent object 
        intent.putExtra("idquiz", idno); 
        intent.putExtra("urlchar", urlChar); 
        Toast.makeText(getActivity(), 
          "Click ListItem Number " +idno+ urlChar, Toast.LENGTH_LONG) 
          .show(); 
        //start the second activity 
        startActivity(intent); 

       } 


      }); 
     } 
    } 

    } 
} 




FATAL EXCEPTION: main 
                     Process: com.example.wonder5.player, PID: 21792 
                     java.lang.NullPointerException 
                      at com.example.wonder5.player.Quizze.aero(Quizze.java:134) 
                      at com.example.wonder5.player.Quizze.access$000(Quizze.java:27) 
                      at com.example.wonder5.player.Quizze$DownloadJSON.onPostExecute(Quizze.java:118) 
                      at com.example.wonder5.player.Quizze$DownloadJSON.onPostExecute(Quizze.java:62) 

Answer 1

IDE warnt Sie führt dazu, dass getView() nicht NULL safe ist Wenn Sie ändern:

ListView listView = (ListView) getView().findViewById(R.id.list4); 

zu:

ListView listView; 
View view = getView(); 
if(view != null){ 
listView = (ListView) view .findViewById(R.id.list4); 
} 

Sie bekommen es nicht mehr