Объект ViewPager с нулевой ссылкой на скрытый фрагмент

Question

Я использую пример, предоставленный студией Android для активности с вкладками, и я изменяю его на фрагмент.

По какой-то причине объект ViewPager имеет нулевую ссылку, когда я пытаюсь извлечь ее из идентификатора.

Вот код:

public class POI extends Fragment implements ActionBar.TabListener { 

    SectionsPagerAdapter mSectionsPagerAdapter; 
    ViewPager mViewPager; 

    public static POI newInstance() { 
     POI fragment = new POI(); 
     return fragment; 
    } 


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

    final ActionBar actionBar = ((AppCompatActivity) getActivity()).getSupportActionBar(); 
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); 

    mSectionsPagerAdapter = new SectionsPagerAdapter(getActivity().getSupportFragmentManager()); 

    mViewPager = (ViewPager) getView().findViewById(R.id.pager); 
    mViewPager.setAdapter(mSectionsPagerAdapter); 

    mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() { 
     @Override 
     public void onPageSelected(int position) { 
      actionBar.setSelectedNavigationItem(position); 
     } 
    }); 

    for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) { 

     int resourceName = getResources().getIdentifier("POI_Section" + i, "string", getActivity().getPackageName()); 
     actionBar.addTab(
       actionBar.newTab() 
         .setText(resourceName) 
         .setTabListener(this)); 
    } 
    actionBar.setDisplayShowHomeEnabled(false); 
    actionBar.setDisplayShowTitleEnabled(false); 

    return rootView; 
} 

Вот лог:

12-10 20:29:14.506 1297-1297/abff.googlemapsappteste E/AndroidRuntime﹕ FATAL EXCEPTION: main 
Process: abff.googlemapsappteste, PID: 1297 
java.lang.RuntimeException: Unable to start activity ComponentInfo{abff.googlemapsappteste/abff.googlemapsappteste.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.support.v4.view.ViewPager.toString()' on a null object reference 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2442) 
     at android.app.ActivityThread.access$800(ActivityThread.java:156) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1351) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:211) 
     at android.app.ActivityThread.main(ActivityThread.java:5389) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:372) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1020) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:815) 
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.support.v4.view.ViewPager.toString()' on a null object reference 
     at abff.googlemapsappteste.POI.onCreateView(POI.java:49) 
     at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962) 
     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1026) 
     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1207) 
     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738) 
     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1572) 
     at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:330) 
     at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:511) 
     at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1236) 
     at android.app.Activity.performStart(Activity.java:6006) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2342) 
      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2442) 
     at android.app.ActivityThread.access$800(ActivityThread.java:156) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1351) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:211) 
     at android.app.ActivityThread.main(ActivityThread.java:5389) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:372) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1020) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:815) 

Answer 1

с вашей XML было бы полезно, но за исключением, что попытаться изменить

mViewPager = (ViewPager) getView().findViewById(R.id.pager); 

в

mViewPager = (ViewPager) rootView.findViewById(R.id.pager);