title: getChildFragmentManager () cannot be resolved or cannot be referenced
body: <p><strong>I know, there are many forum posts on this topic already, but none did solve my issue</strong></p>
  
  <p>My code looks like this:</p>
  
  <pre><code>private SectionsPagerAdapter myAdapt;
  private ViewPager myPager;
  ....
  
      @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_home_screen);
  
      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.
      if (mSectionsPagerAdapter == null) {
          mSectionsPagerAdapter = new SectionsPagerAdapter(getChildFragmentManager());
      }
      // Set up the ViewPager with the sections adapter.
      mViewPager = (ViewPager) findViewById(R.id.container);
      mViewPager.setAdapter(mSectionsPagerAdapter);
  ....
  </code></pre>
  
  <p>But I get the <code>Cannot resolve method getChildFragmentManager ()</code> which seems to make many problems.</p>
  
  <p>I already tried a pretty whole lot of things:</p>
  
  <ul>
  <li>I checked the inbound support library for the correct version.</li>
  <li>I tried to reference the method as <code>android.support.v7.app.getChildFragmentManager()</code> which got me the <code>Cannot make static reference from non-static context</code> error.</li>
  <li>I reimported the v4 support library </li>
  </ul>
  
  <p><strong>The whole issue arose because the Fragments turn empty whenever I return to the activity. If you have another idea, feel free to answer or comment it, then the whole issue regarding the getChildFragmentManager is solved anyway</strong></p>
  
  <p>I have no clue what to do...</p>
  
  <p>ps: here is the whole class implementation:</p>
  
  <pre><code>import android.support.v4.app.FragmentManager;
  import android.content.Intent;
  import android.os.AsyncTask;
  import android.support.design.widget.TabLayout;
  import android.support.design.widget.FloatingActionButton;
  import android.support.design.widget.Snackbar;
  import android.support.v4.app.Fragment;
  import android.support.v7.app.AppCompatActivity;
  import android.support.v7.widget.Toolbar;
  
  import android.support.v4.app.FragmentPagerAdapter;
  import android.support.v4.view.ViewPager;
  import android.os.Bundle;
  
  import android.util.Log;
  import android.view.LayoutInflater;
  import android.view.Menu;
  import android.view.MenuItem;
  import android.view.View;
  
  
  public class HomeScreen extends AppCompatActivity {
  
      int index = 0;
      int semIndex = 0;
  
      public static final String GROUP_EXTRA = "Group";
      public static final String HOME_SCREEN_LOG = "HomeScreen Activity";
  
      /**
       * 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;
  
      LayoutInflater inflater;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_home_screen);
  
          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.
          if (mSectionsPagerAdapter == null) {
              mSectionsPagerAdapter = new SectionsPagerAdapter(getChildFragmentManager());
          }
          // 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);
  
          final Bundle b;
          if ((b =this.getIntent().getExtras()) != null) {
              AsyncTask at = new AsyncTask() {
                  @Override
                  protected Object doInBackground(Object[] params) {
  
                      String  groupName = b.getString(HomeScreen.GROUP_EXTRA),
                              desc = b.getString(NewEditGroupActivity.DESC_EXTRA),
                              time = b.getString(NewEditGroupActivity.TIME_EXTRA),
                              date = b.getString(NewEditGroupActivity.DATE_EXTRA);
  
                      int numOfPart = b.getInt(NewEditGroupActivity.NUM_EXTRA);
  
                      boolean regular = b.getBoolean(NewEditGroupActivity.IS_NEW);
  
                      ExpandListChild elc = new ExpandListChild(desc,String.valueOf(numOfPart),date,time,regular);
                      ExpandListGroup elg = new ExpandListGroup(groupName);
  
                      MyLgFragment lf = (MyLgFragment) mSectionsPagerAdapter.getItem(0);
                      AllLgFragment af = (AllLgFragment) mSectionsPagerAdapter.getItem(1);
  
                      af.add(elc,elg);
                      lf.add(elc,elg);
                      return null;
                  }
              };
          }
  
          mViewPager = (ViewPager) findViewById(R.id.container);
          mViewPager.setAdapter(mSectionsPagerAdapter);    
          inflater = getLayoutInflater();
      }
  
  
      @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_home_screen, 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.action_settings) {
              return true;
          }
  
          return super.onOptionsItemSelected(item);
      }
  }
  </code></pre>
  
  <p>Let me know if you need further information.</p>