Android getSupportFragmentManager NULL pointer exception in Fragment

Question

i'm trying to display new fragment with TabBar and View Pager after click on the Navigation drawer item.

Problem is that newly created Fragment is causing NULL pointer exception on

viewPager.setAdapter(mAdapter);

I'm stucked on swipeable-views with tabs in Fragment a several hours but without luck, can somebody helps me with this problem please?

For swipable views i followed this tutorial:

http://www.androidhive.info/2013/10/android-tab-layout-with-swipeable-views-1/

Code of the fragment is here:

import android.app.ActionBar;
import android.support.v4.app.Fragment;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import eu.com.mycompany.adapter.TabsPagerAdapter;

public class Fragment_AboutApplication extends Fragment implements ActionBar.TabListener {

    public Fragment_AboutApplication(){}
    private ViewPager viewPager;
    private TabsPagerAdapter mAdapter;
    private ActionBar actionBar;
    // Tab titles
    private String[] tabs = { "Top Rated", "Games", "Movies" };

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

        View rootView = inflater.inflate(R.layout.fragment_about_app, container, false);


        // Initilization
        viewPager = (ViewPager) getActivity().findViewById(R.id.pager);
        actionBar = getActivity().getActionBar();
        mAdapter = new TabsPagerAdapter(getActivity().getSupportFragmentManager());

        /*HERE IS THROWED NULL POINTER EXCEPTION*/ 
        viewPager.setAdapter(mAdapter);
        actionBar.setHomeButtonEnabled(false);
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);


        // Adding Tabs
        for (String tab_name : tabs) {
            actionBar.addTab(actionBar.newTab().setText(tab_name)
                    .setTabListener(this));
        }
        return rootView;
    }

    @Override
    public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

    }

    @Override
    public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

    }
}

Class TabPagerAdapter:

public class TabsPagerAdapter extends FragmentPagerAdapter {

    public TabsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int index) {

        switch (index) {
            case 0:
                // Top Rated fragment activity
                return new Fragment_TopRated();
            case 1:
                // Games fragment activity
                return new Fragment_TopRated();
            case 2:
                // Movies fragment activity
                return new Fragment_TopRated();
        }

        return null;
    }

    @Override
    public int getCount() {
        // get item count - equal to number of tabs
        return 3;
    }

}

Main fragment layout with View Pager

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </android.support.v4.view.ViewPager>

    <TextView
        android:id="@+id/txtLabel"
         android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:textSize="16dp"
        android:text="Settings"/>

    <ImageView android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/txtLabel"
        android:src="@drawable/ic_communities"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="10dp"/>    

</RelativeLayout>

Exception is:

E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.NullPointerException
    at android.support.v4.app.Fragment.performCreateView(Fragment.java:1504)
                at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:942)
                at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1121)
                at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
                at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1484)
                at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:450)
                at android.os.Handler.handleCallback(Handler.java:725)
                at android.os.Handler.dispatchMessage(Handler.java:92)
                at android.os.Looper.loop(Looper.java:153)
                at android.app.ActivityThread.main(ActivityThread.java:5330)
                at java.lang.reflect.Method.invokeNative(Native Method)
                at java.lang.reflect.Method.invoke(Method.java:511)
                at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:608)
                at dalvik.system.NativeStart.main(Native Method)

Answer 1

change:

mAdapter = new TabsPagerAdapter(getActivity().getSupportFragmentManager())

to:

 mAdapter = new TabsPagerAdapter(getChildFragmentManager())

when you are using fragment inside another fragment you must use ChildFragmentManager not FragmentManager.