NullPointerException on setMenuVisibility

Question

Ich folge dem nächsten Tutorial, um eine Registerkarte http://www.truiton.com/2015/06/android-tabs-example-fragments-viewpager/ einzufügen. Mein Problem ist, dass ich versuche, es in ein Fragment einzufügen, nicht in eine Aktivität, aber ich bekomme den nächsten Fehler.

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.app.Fragment.setMenuVisibility(boolean)' on a null object reference 
    at android.support.v4.app.FragmentStatePagerAdapter.instantiateItem(FragmentStatePagerAdapter.java:116) 
    at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:943) 
    at android.support.v4.view.ViewPager.populate(ViewPager.java:1157) 
    at android.support.v4.view.ViewPager.populate(ViewPager.java:1025) 
    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1545) 
    at android.view.View.measure(View.java:18797) 
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) 
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1458) 
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:746) 
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:629) 
    at android.view.View.measure(View.java:18797) 
    at android.widget.ScrollView.measureChildWithMargins(ScrollView.java:1283) 
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) 
    at android.widget.ScrollView.onMeasure(ScrollView.java:340) 
    at android.view.View.measure(View.java:18797) 
    at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715) 
    at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461) 
    at android.view.View.measure(View.java:18797) 
    at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715) 
    at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461) 
    at android.view.View.measure(View.java:18797) 
    at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715) 
    at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461) 
    at android.view.View.measure(View.java:18797) 
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) 
    at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:668) 
    at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:735) 
    at android.view.View.measure(View.java:18797) 
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) 
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) 
    at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135) 
    at android.view.View.measure(View.java:18797) 
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) 
    at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:391) 
    at android.view.View.measure(View.java:18797) 
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) 
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) 
    at android.view.View.measure(View.java:18797) 
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) 
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1458) 
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:746) 
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:629) 
    at android.view.View.measure(View.java:18797) 
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951) 
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) 
    at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2658) 
    at android.view.View.measure(View.java:18797) 
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2108) 
    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1224) 
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1460) 
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1115) 
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6023) 
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858) 
    at android.view.Choreographer.doCallbacks(Choreographer.java:670) 
    at android.view.Choreographer.doFrame(Choreographer.java:606) 
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844) 
at an... 

Das Fragment, das das TabHost und die viewpager enthält, ist die nächste:

public class AdministrarFragment extends Fragment { 

    public static final String TAG = "AdministrarFragment"; 
    private FragmentIterationListener mCallback = null; 
    public interface FragmentIterationListener{ 
     public void onFragmentIteration(Bundle parameters); 
    } 

    public static AdministrarFragment newInstance(Bundle arguments){ 
     AdministrarFragment f = new AdministrarFragment(); 
     if(arguments != null){ 
      f.setArguments(arguments); 
     } 
     return f; 
    } 

    public AdministrarFragment(){ 

    } 

    //El fragment se ha adjuntado al Activity 
    @Override 
    public void onAttach(Context context) { 
     super.onAttach(context); 

     Activity activity = context instanceof Activity ? (Activity) context : null; 
    } 

    //El Fragment ha sido quitado de su Activity y ya no está disponible 
    @Override 
    public void onDetach() { 
     super.onDetach(); 
    } 

    //La vista ha sido creada y cualquier configuración guardada está cargada 
    @Override 
    public void onViewStateRestored(Bundle savedInstanceState) { 
     super.onViewStateRestored(savedInstanceState); 
    } 

    //El Activity que contiene el Fragment ha terminado su creación 
    @Override 
    public void onActivityCreated(Bundle savedInstanceState) { 
     super.onActivityCreated(savedInstanceState); 
    } 

    //El fragment se ha adjuntado al Activity 
    @Override 
    public void onAttach(Activity activity) { 
     super.onAttach(activity); 

     mCallback = (FragmentIterationListener) activity; 

    } 

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

     TabLayout tabLayout = (TabLayout) view.findViewById(R.id.tab_layout); 
     tabLayout.addTab(tabLayout.newTab().setText(getString(R.string.tiempo))); 
     tabLayout.addTab(tabLayout.newTab().setText(getString(R.string.gastos))); 
     tabLayout.setTabGravity(TabLayout.GRAVITY_FILL); 

     final ViewPager viewPager = (ViewPager) view.findViewById(R.id.pager); 
     final AdministrarPageAdapter adapter = new AdministrarPageAdapter(getActivity().getSupportFragmentManager(), tabLayout.getTabCount()); 
     viewPager.setAdapter(adapter); 
     viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout)); 
     tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() { 
      @Override 
      public void onTabSelected(TabLayout.Tab tab) { 
       viewPager.setCurrentItem(tab.getPosition()); 
      } 

      @Override 
      public void onTabUnselected(TabLayout.Tab tab) { 

      } 

      @Override 
      public void onTabReselected(TabLayout.Tab tab) { 

      } 
     }); 

     return view; 
    } 
} 

Und das ist mein Pageadapter:

public class AdministrarPageAdapter extends FragmentStatePagerAdapter { 
    int mNumOfTabs; 

    public AdministrarPageAdapter(FragmentManager fm, int NumOfTabs) { 
     super(fm); 
     this.mNumOfTabs = NumOfTabs; 
    } 

    @Override 
    public Fragment getItem(int position) { 

     switch (position) { 
      case 0: 
       AdministrarTiemposFragment tab_tiempos = new AdministrarTiemposFragment(); 
       return tab_tiempos; 
      /*case 1: 
       TabFragment2 tab2 = new TabFragment2(); 
       return tab2; 
      case 2: 
       TabFragment3 tab3 = new TabFragment3(); 
       return tab3;*/ 
      default: 
       return null; 
     } 
    } 

    @Override 
    public int getCount() { 
     return mNumOfTabs; 
    } 
} 

Answer 1

Ich habe so etwas wie dies stattdessen getan hätte. Könnte das Problem nicht lösen, aber probiere es aus, da wahrscheinlich dein switch: default aufgerufen wird. Fragmente in der Liste sollten in der Reihenfolge hinzugefügt werden, in der sie angezeigt werden sollen.

public class AdministrarPageAdapter extends FragmentStatePagerAdapter { 
     List<Fragment> mFragments; 

     public AdministrarPageAdapter(FragmentManager fm, List<Fragment> fragments) { 
      super(fm); 
      this.mFragments = fragments; 
     } 

     @Override 
     public Fragment getItem(int position) { 
      return mFragments.get(position); 
     } 

     @Override 
     public int getCount() { 
      return mFragments.size(); 
     } 
    } 

In Ihrem Fragmente, die Liste vor dem Adapter initialisieren

final ViewPager viewPager = (ViewPager) view.findViewById(R.id.pager); 

List<Fragment> fragments = new ArrayList<>(); 
fragments.add(new AdministrarTiemposFragment());  

final AdministrarPageAdapter adapter = new AdministrarPageAdapter(getActivity().getSupportFragmentManager(), fragments); 
viewPager.setAdapter(adapter); 

oder eine Methode auf dem Adapter, die Fragmente in eine Liste hinzufügen, die in dem Adapter contructor initialisiert wird.

final ViewPager viewPager = (ViewPager) view.findViewById(R.id.pager); 
final AdministrarPageAdapter adapter = new AdministrarPageAdapter(getActivity().getSupportFragmentManager()); 
adapter.addFragment(new AdministrarTiemposFragment()); 
viewPager.setAdapter(adapter);