Puntatore nullo su visualizzazione gonfiata quando si carica per la seconda volta un frammento di mappa di google

Question

Sto utilizzando un DrawerLayout e quando carico per la seconda volta un frammento di mappa di google, l'eccezione verrà catturata come previsto; tuttavia, più avanti nello stesso metodo quando provo

Button btnShowList = (Button) ui.findViewById(R.id.btnShowList); 

e ottengo un'eccezione di puntatore nullo. Immagino che sia perché allo ui non è stato assegnato alcun valore.

Come posso gestire questo?

Page2.java:

public class Page2 extends Fragment { 

    View ui; 
    final String TAG = "POPE"; 
    final int CODIGO_DE_RESULTADO_1 = 1; // Es para usarlo en onActivityResult(); 

    private GoogleMap mMap; 

    public Page2(){ 
     // Este es el constructor 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 

     if (ui != null) { 
      ViewGroup parent = (ViewGroup) ui.getParent(); 
      if (parent != null){ 
       parent.removeView(ui); 
      } 
     } 

     try { 
      ui = inflater.inflate(R.layout.activity_page2,container,false); 
     } catch (InflateException e) { 
      Log.i(TAG,"HERE COMES THE STACK TRACE"); 
      e.printStackTrace(); 
     } 

     FragmentManager fm = getFragmentManager(); 
     mMap = ((MapFragment) fm.findFragmentById(R.id.map)).getMap(); 
     mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);  
     mMap.setMyLocationEnabled(true); 


     Button btnShowList = (Button) ui.findViewById(R.id.btnShowList); 
     btnShowList.setOnClickListener(new View.OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       showFileslist(); 
      } 
     }); 

     return ui; 

    } 
} 

activity_page2.xml:

<RelativeLayout 
android:layout_width="fill_parent" 
android:layout_height="fill_parent" 
xmlns:android="http://schemas.android.com/apk/res/android"> 

<fragment 
    android:id="@+id/map" 
    android:name="com.google.android.gms.maps.MapFragment" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" /> 

<Button 
    android:id="@+id/btnShowList" 
    style="?android:attr/buttonStyleSmall" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentLeft="true" 
    android:layout_alignParentTop="true" 
    android:text="Load points" /> 

Log:

07-08 22:17:44.203: I/POPE(11859): HERE COMES THE STACK TRACE 
07-08 22:17:44.213: W/System.err(11859): android.view.InflateException: Binary XML file line #6: Error inflating class fragment 
07-08 22:17:44.213: W/System.err(11859): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:710) 
07-08 22:17:44.213: W/System.err(11859): at android.view.LayoutInflater.rInflate(LayoutInflater.java:752) 
07-08 22:17:44.213: W/System.err(11859): at android.view.LayoutInflater.inflate(LayoutInflater.java:495) 
07-08 22:17:44.213: W/System.err(11859): at android.view.LayoutInflater.inflate(LayoutInflater.java:397) 
07-08 22:17:44.213: W/System.err(11859): at com.jorgeandresserrano.gpstools.Page2.onCreateView(Page2.java:52) 
07-08 22:17:44.213: W/System.err(11859): at android.app.Fragment.performCreateView(Fragment.java:1695) 
07-08 22:17:44.213: W/System.err(11859): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:903) 
07-08 22:17:44.213: W/System.err(11859): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1075) 
07-08 22:17:44.213: W/System.err(11859): at android.app.BackStackRecord.run(BackStackRecord.java:682) 
07-08 22:17:44.213: W/System.err(11859): at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1455) 
07-08 22:17:44.223: W/System.err(11859): at android.app.FragmentManagerImpl$1.run(FragmentManager.java:441) 
07-08 22:17:44.223: W/System.err(11859): at android.os.Handler.handleCallback(Handler.java:725) 
07-08 22:17:44.223: W/System.err(11859): at android.os.Handler.dispatchMessage(Handler.java:92) 
07-08 22:17:44.223: W/System.err(11859): at android.os.Looper.loop(Looper.java:137) 
07-08 22:17:44.223: W/System.err(11859): at android.app.ActivityThread.main(ActivityThread.java:5293) 
07-08 22:17:44.223: W/System.err(11859): at java.lang.reflect.Method.invokeNative(Native Method) 
07-08 22:17:44.223: W/System.err(11859): at java.lang.reflect.Method.invoke(Method.java:511) 
07-08 22:17:44.223: W/System.err(11859): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102) 
07-08 22:17:44.223: W/System.err(11859): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869) 
07-08 22:17:44.223: W/System.err(11859): at dalvik.system.NativeStart.main(Native Method) 
07-08 22:17:44.223: W/System.err(11859): Caused by: java.lang.IllegalArgumentException: Binary XML file line #6: Duplicate id 0x7f05003f, tag null, or parent id 0xffffffff with another fragment for com.google.android.gms.maps.MapFragment 
07-08 22:17:44.223: W/System.err(11859): at android.app.Activity.onCreateView(Activity.java:4863) 
07-08 22:17:44.233: W/System.err(11859): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:686) 
07-08 22:17:44.233: W/System.err(11859): ... 19 more 
07-08 22:17:44.233: D/AndroidRuntime(11859): Shutting down VM 
07-08 22:17:44.233: W/dalvikvm(11859): threadid=1: thread exiting with uncaught exception (group=0x410feac8) 
07-08 22:17:44.233: E/AndroidRuntime(11859): FATAL EXCEPTION: main 
07-08 22:17:44.233: E/AndroidRuntime(11859): java.lang.NullPointerException 
07-08 22:17:44.233: E/AndroidRuntime(11859): at com.myname.myapp.Page2.onCreateView(Page2.java:66) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at android.app.Fragment.performCreateView(Fragment.java:1695) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:903) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1075) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at android.app.BackStackRecord.run(BackStackRecord.java:682) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1455) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at android.app.FragmentManagerImpl$1.run(FragmentManager.java:441) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at android.os.Handler.handleCallback(Handler.java:725) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at android.os.Handler.dispatchMessage(Handler.java:92) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at android.os.Looper.loop(Looper.java:137) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at android.app.ActivityThread.main(ActivityThread.java:5293) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at java.lang.reflect.Method.invokeNative(Native Method) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at java.lang.reflect.Method.invoke(Method.java:511) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869) 
07-08 22:17:44.233: E/AndroidRuntime(11859): at dalvik.system.NativeStart.main(Native Method) 

Linea 66 è:

Button btnShowList = (Button) ui.findViewById(R.id.btnShowList); 

Answer 1

Il problema può essere risolto rimuovendo il frammento di mappa nel metodo onDestroyView() poco prima di uscire. Come questo:

@Override 
public void onDestroyView() { 
    super.onDestroyView(); 
    MapFragment f = (MapFragment) getFragmentManager().findFragmentById(R.id.map); 
    if (f != null){ 
     getFragmentManager().beginTransaction().remove(f).commit(); 
    } 
} 

Questo post spiega più in dettaglio https://stackoverflow.com/a/14484640/2422833

Answer 2

Come sull'utilizzo OnResume per il frammento. Fai riferimento al tuo ui. E OnResume controlla nuovamente che l'oggetto ui è nullo o no, quindi lo gonfia nuovamente. Dal momento che ha chiamato la seconda volta, c'è la possibilità che non riesca più a visitare il tuo onCreateView.