title: OnResume() not called in Fragment using tabLayout and ViewPager
body: <p>i'm developing an app using <code>tabLayout</code>.</p>
  
  <p>I've a problem: When I try to reactivate a <code>Fragment</code>, the method <code>OnResume</code> is non called. </p>
  
  <p>This is my activity:</p>
  
  <pre><code> private void init() {
      fab = (FloatingActionButton) findViewById(R.id.fab);
      fab.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View view) {
              Snackbar.make(view, "Nuovo Ticket", Snackbar.LENGTH_LONG)
                      .setAction("Action", null).show();
          }
      });
  
  
      TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout);
      tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);
  
      final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
      final PagerAdapter adapter = new PagerAdapter
              (getSupportFragmentManager(), tabLayout.getTabCount());
      viewPager.setAdapter(adapter);
  
      tabLayout.setupWithViewPager(viewPager);
  }
  </code></pre>
  
  <p>I use a FragmentStatePagerAdapter like this:</p>
  
  <pre><code>public class PagerAdapter extends FragmentStatePagerAdapter {
  int mNumOfTabs;
  
  public PagerAdapter(FragmentManager fm, int NumOfTabs) {
      super(fm);
      this.mNumOfTabs = NumOfTabs;
  }
  
  @Override
  public Fragment getItem(int position) {
  
      switch (position) {
          case 0:
              return new LavorazioneFragment();
          case 1:
              return new PendingFragment();
          case 2:
              return new StoriciFragment();
          default:
              return null;
      }
  }
  
  @Override
  public int getCount() {
      return mNumOfTabs;
  }
  </code></pre>
  
  <p>}</p>
  
  <p>When i reactivate the <code>TAB1</code> Fragment from <code>TAB3</code> Fragment (the last one), the <code>OnResume</code> Method is called. But, for example, </p>
  
  <p>When I try to reactivate the first tab from the second, never called.</p>