How to create a Tabbed Activity with ListViews - Android
<p>First of all, I'm a beginner in Android programming. What I'm trying to do is to program three Tabs with each a ListView inside (you know it from e.g. WhatsApp). Android Studio makes it easy to automatically create a Tabbed Activity. So the question is: how can I implement a ListView for each Tab? 
Actually there is a nice tutorial on <a href="http://www.androidhive.info/2012/05/android-combining-tab-layout-and-list-view/" rel="nofollow">http://www.androidhive.info/2012/05/android-combining-tab-layout-and-list-view/</a> which uses TabActivity. However this method is deprecated and Fragments should be used instead. I have extended main_fragment.xml (which was created by Android Studio) with a ListView. But what is the correct way to set the corresponding list adapters and especially where to set them? Setting them like <code>ListView list_all = (ListView) findViewById(R.id.listViewAll)</code> in <code>onCreate()</code> does not work because of a null object reference error. Also I didn't find out how to use the <code>rootView</code> which is returned by <code>onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState)</code> So how can I solve this problem?</p>

<p>main_fragment.xml:</p>

<pre><code>&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:background="@color/colorAccent"
    android:paddingTop="@dimen/activity_vertical_margin"&gt;

    &lt;ListView
        android:id="@+id/listViewAll"
        android:layout_width="match_parent"
        android:layout_height="match_parent"&gt;&lt;/ListView&gt;

&lt;/RelativeLayout&gt;
</code></pre>

<p>main.xml:</p>

<pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;

&lt;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"
    android:background="@color/white"

    tools:context="de.url.members"&gt;

    &lt;android.support.design.widget.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingTop="@dimen/appbar_padding_top"
        android:background="@color/bg_login_dark"
        android:theme="@style/AppTheme.AppBarOverlay"&gt;

        &lt;android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/bg_login_dark"
            app:layout_scrollFlags="scroll|enterAlways"
            app:popupTheme="@style/AppTheme.PopupOverlay"&gt;

        &lt;/android.support.v7.widget.Toolbar&gt;

        &lt;android.support.design.widget.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:tabMaxWidth="0dp"
            app:tabGravity="fill"
            app:tabMode="fixed"
            android:fillViewport="false" /&gt;

    &lt;/android.support.design.widget.AppBarLayout&gt;

    &lt;android.support.v4.view.ViewPager
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" /&gt;

    &lt;android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="end|bottom"
        android:layout_margin="@dimen/fab_margin"
        android:src="@android:drawable/ic_dialog_email" /&gt;

&lt;/android.support.design.widget.CoordinatorLayout&gt;
</code></pre>

<p>main.java:</p>

<pre><code>public class main extends AppCompatActivity {

    /**
     * The {@link android.support.v4.view.PagerAdapter} that will provide
     * fragments for each of the sections. We use a
     * {@link FragmentPagerAdapter} derivative, which will keep every
     * loaded fragment in memory. If this becomes too memory intensive, it
     * may be best to switch to a
     * {@link android.support.v4.app.FragmentStatePagerAdapter}.
     */
    private SectionsPagerAdapter mSectionsPagerAdapter;


    // The {@link ViewPager} that will host the section contents.
    private ViewPager mViewPager;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);


        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        // Create the adapter that will return a fragment for each of the three
        // primary sections of the activity.
        mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

        // Set up the ViewPager with the sections adapter.
        mViewPager = (ViewPager) findViewById(R.id.container);
        mViewPager.setAdapter(mSectionsPagerAdapter);

        TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(mViewPager);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
            // action here
            }
        });
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_members, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.logout) {
            //action here
        }

        return super.onOptionsItemSelected(item);
    }


    /**
     * A placeholder fragment containing a simple view.
     */

    public static class PlaceholderFragment extends Fragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */
        private static final String ARG_SECTION_NUMBER = "section_number";

        public PlaceholderFragment() {
        }

        /**
         * Returns a new instance of this fragment for the given section
         * number.
         */
        public static PlaceholderFragment newInstance(int sectionNumber) {
            PlaceholderFragment fragment = new PlaceholderFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_SECTION_NUMBER, sectionNumber);
            fragment.setArguments(args);
            return fragment;
        }

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

            int sectionNumber = getArguments().getInt(ARG_SECTION_NUMBER);//INDEX of selected TAB
            View rootView;

            if (sectionNumber == 1){
                rootView = inflater.inflate(R.layout.main_fragment, container, false);
            }else if (sectionNumber == 2){
                rootView = inflater.inflate(R.layout.main_fragment, container, false);                 
            }else if (sectionNumber == 3){
                rootView = inflater.inflate(R.layout.main_fragment, container, false);                  
            }else{
                rootView = inflater.inflate(R.layout.main_fragment, container, false);

            }

            return rootView;
        }
    }

    /**
     * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
     * one of the sections/tabs/pages.
     */
    public class SectionsPagerAdapter extends FragmentPagerAdapter {

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

        @Override
        public Fragment getItem(int position) {
            // getItem is called to instantiate the fragment for the given page.
            // Return a PlaceholderFragment (defined as a static inner class below).
            return PlaceholderFragment.newInstance(position + 1);
        }

        @Override
        public int getCount() {
            // Show 3 total pages.
            return 3;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            switch (position) {
                case 0:
                    return getResources().getString(R.string.title_section1);
                case 1:
                    return getResources().getString(R.string.title_section2);
                case 2:
                    return getResources().getString(R.string.title_section3);
            }
            return null;
        }
    }
}
</code></pre>