NullPointerException in FragmentTransaction

Question

Ich habe ein Layout FrameLayout und ein LinearLayout in MainActivity. Das Linearlayout besteht aus 7 Bildern. Ich ändere Fragmente beim Klicken auf diese Bilder. In einem der Fragmente erhalte ich Werte von json und füge sie in 2 Spinner ein. Das erste Mal, wenn ich das Fragment von diesem Fragment zu irgendeinem anderen Fragment ändere, funktioniert es gut. Aber wenn ich zum zweiten Mal zu diesem Fragment zurückkehre und dann das Fragment ändere, stürzt die App mit einer NPE ab. Was mache ich in meiner MainActivity falsch?

Logcat:

FATAL EXCEPTION: main 
Process: com.rishta.rishtabliss, PID: 26506 
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference 
at android.view.LayoutInflater.from(LayoutInflater.java:228) 
at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:178) 
at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:163) 
at com.rishta.rishtabliss.fragment.FragmentTwo$1.onResponse(FragmentTwo.java:81) 
at com.rishta.rishtabliss.fragment.FragmentTwo$1.onResponse(FragmentTwo.java:64) 
at com.android.volley.toolbox.StringRequest.deliverResponse(StringRequest.java:60) 
at com.android.volley.toolbox.StringRequest.deliverResponse(StringRequest.java:30) 
at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:99) 
at android.os.Handler.handleCallback(Handler.java:746) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5443) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 

activity_main.xml

<?xml version="1.0" encoding="utf-8"?> 
    <android.support.design.widget.CoordinatorLayout 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:id="@+id/main_content" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:fitsSystemWindows="true" 
     tools:context=".activity.MainActivity"> 

     <RelativeLayout 
      android:layout_width="match_parent" 
      android:layout_height="match_parent" 
      android:orientation="vertical"> 

      <LinearLayout 
       android:id="@+id/llfooter" 
       android:background="#ffffff" 
       android:layout_alignParentBottom="true" 
       android:orientation="horizontal" 
       android:layout_width="match_parent" 
       android:layout_height="45dp"> 

       <ImageView 
        android:id="@+id/img1" 
        android:layout_weight="1" 
        android:src="@drawable/number_one" 
        android:layout_width="match_parent" 
        android:layout_height="wrap_content" 
        android:onClick="selectFrag"/> 
       <ImageView 
        android:id="@+id/img2" 
        android:layout_weight="1" 
        android:src="@drawable/number_two" 
        android:layout_width="match_parent" 
        android:layout_height="wrap_content" 
        android:onClick="selectFrag"/> 
       <ImageView 
        android:id="@+id/img3" 
        android:layout_weight="1" 
        android:src="@drawable/number_three" 
        android:layout_width="match_parent" 
        android:layout_height="wrap_content" 
        android:onClick="selectFrag"/> 
       <ImageView 
        android:id="@+id/img4" 
        android:layout_weight="1" 
        android:src="@drawable/number_four" 
        android:layout_width="match_parent" 
        android:layout_height="wrap_content" 
        android:onClick="selectFrag"/> 
       <ImageView 
        android:id="@+id/img5" 
        android:layout_weight="1" 
        android:src="@drawable/number_five" 
        android:layout_width="match_parent" 
        android:layout_height="wrap_content" 
        android:onClick="selectFrag"/> 
       <ImageView 
        android:id="@+id/img6" 
        android:layout_weight="1" 
        android:src="@drawable/number_six" 
        android:layout_width="match_parent" 
        android:layout_height="wrap_content" 
        android:onClick="selectFrag"/> 
       <ImageView 
        android:id="@+id/img7" 
        android:layout_weight="1" 
        android:src="@drawable/number_seven" 
        android:layout_width="match_parent" 
        android:layout_height="wrap_content" 
        android:onClick="selectFrag"/> 

      </LinearLayout> 

      <FrameLayout 
       android:id="@+id/frame_main" 
       android:layout_width="match_parent" 
       android:layout_height="match_parent" 
       android:layout_alignParentTop="true" 
       android:layout_above="@+id/llfooter" /> 

     </RelativeLayout> 
    </android.support.design.widget.CoordinatorLayout> 

Hauptaktivität:

public class MainActivity extends AppCompatActivity { 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     if (findViewById(R.id.frame_main) != null) { 
      if (savedInstanceState != null) { 
       return; 
      } 

      FragmentOne firstFragment = new FragmentOne(); 
      getSupportFragmentManager().beginTransaction().add(R.id.frame_main, firstFragment).commit(); 
     } 


    } //End OnCreate Method 


    public void selectFrag(View view) { 
     FragmentManager fm = getSupportFragmentManager(); 

     Fragment currentFragment = fm.findFragmentById(R.id.frame_main); 
     Fragment newFragment = null; 

     switch (view.getId()) { 
      case R.id.img1: 
       if (currentFragment instanceof FragmentOne) { 
        return; 
       } 
       newFragment = new FragmentOne(); 
       break; 
      case R.id.img2: 
       if (currentFragment instanceof FragmentTwo) { 
        return; 
       } 
       newFragment = new FragmentTwo(); 
       break; 
      case R.id.img3: 
       if (currentFragment instanceof FragmentThree) { 
        return; 
       } 
       newFragment = new FragmentThree(); 
       break; 
      case R.id.img4: 
       if (currentFragment instanceof FragmentFour) { 
        return; 
       } 
       newFragment = new FragmentFour(); 
       break; 
      case R.id.img5: 
       if (currentFragment instanceof FragmentFive) { 
        return; 
       } 
       newFragment = new FragmentFive(); 
       break; 
      case R.id.img6: 
       if (currentFragment instanceof FragmentSix) { 
        return; 
       } 
       newFragment = new FragmentSix(); 
       break; 
      case R.id.img7: 
       if (currentFragment instanceof FragmentSeven) { 
        return; 
       } 
       newFragment = new FragmentSeven(); 
       break; 
     } 

     FragmentTransaction fragmentTransaction = fm.beginTransaction(); 
     fragmentTransaction.replace(R.id.frame_main, newFragment); 
     fragmentTransaction.commit(); 
    } 


} 

Fragment:

public class FragmentTwo extends Fragment { 

     private Spinner religion, subreligion, mtoungue; 
     private List<String> religionlist; 

     @Override 
     public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
      return inflater.inflate(R.layout.fragment_two, container, false); 

     } 

     @Override 
     public void onViewCreated(View view, @Nullable Bundle savedInstanceState) { 
      super.onViewCreated(view, savedInstanceState); 

      religion = (Spinner)view.findViewById(R.id.spinner_religion); 
      fetchlist(); 

     } 

     private void fetchlist() { 

      StringRequest stringRequest = new StringRequest(Request.Method.GET, URLUtils.SIGNUP_COTAIN_URL, new Response.Listener<String>() { 

       @Override 
       public void onResponse(String response) { 
        Log.e("ResponceFragmentTwo","***********************"+response); 
        try { 


         religionlist = new ArrayList<String>(); 

         JSONObject jo = new JSONObject(response); 
         JSONArray arr = jo.getJSONArray("all_religion"); 
         for (int i = 0; i < arr.length(); i++) { 
          JSONObject obj = arr.getJSONObject(i); 
          religionlist.add(obj.getString("name")); 
         } 

         religion.setAdapter(new ArrayAdapter<String>(getActivity(), R.layout.spinner_item, religionlist)); 



        } catch (JSONException e) { 
         // TODO Auto-generated catch block 
         e.printStackTrace(); 
        } 

       } 
      }, new Response.ErrorListener() { 
       @Override 
       public void onErrorResponse(VolleyError error) { 
        Toast.makeText(getActivity(), "VolleyError" + error.toString(), Toast.LENGTH_LONG).show(); 
       } 


      }) { 



      }; 

      RequestQueue requestQueue = Volley.newRequestQueue(getActivity()); 
      requestQueue.add(stringRequest); 

     } 


    } 

Answer 1

Nach etwas mehr auf den Code der Suche bin ich ziemlich sicher, dass der Kern Ihrer Frage ist, dass getActivity() kehrt null wenn die reponse geliefert wird. Das liegt wahrscheinlich daran, dass das Fragment nicht mehr an Ihre Aktivität angehängt ist (d. H. Sie haben replace mit einem anderen Fragment aufgerufen).

Es ist wahrscheinlich am besten für null zu überprüfen, bevor setAdapter zu nennen (obwohl ich keine Ahnung, ob dass keine unerwünschten Folgen für die Funktionalität hat):

if (getActivity() != null) { 
    religion.setAdapter(new ArrayAdapter<String>(getActivity(), R.layout.spinner_item, religionlist)); 
}