title: findFragmentByTag returns null on all fragments except one
body: <p>I know there are some questions that cover this issue, but mines kind of different because it doesn't use <code>fragment</code> transition (I don't know how it works so I didnt use it).</p>
  
  <p>What my <code>MainActivity</code> does is, it adds <code>fragments</code> on the <code>tabBar</code> and creates functions to pass in a message data from one <code>fragment</code> to another <code>fragment</code>. </p>
  
  <pre><code>public class MainActivity extends AppCompatActivity implements InputTab.SendMessage, FollowingTab.SendMessage, FollowerTab.SendMessage, ProfileTab.SendMessage, UserSearchResultTab.SendMessage {
  
      private SectionsPageAdapter pageAdapter;
      ViewPager viewPager;
      public static String currentUser;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  
          FragmentManager fragmentManager = getSupportFragmentManager();
          FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
          fragmentTransaction.replace(R.id.container, new ProfileTab());
  
          fragmentTransaction.commit();
  
          pageAdapter = new SectionsPageAdapter(getSupportFragmentManager());
  
          // Sets up the ViewPager with the sections adapter
  
          viewPager = (ViewPager) findViewById(R.id.container);
          setupViewPager(viewPager);
  
          TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
          tabLayout.setupWithViewPager((viewPager));
  
      }
  
      // Adds fragments to SectionsPageAdapter and gives names for the corresponding tab
  
      private void setupViewPager(ViewPager viewPager) {
          SectionsPageAdapter adapter = new SectionsPageAdapter(getSupportFragmentManager());
          adapter.addFragment(new InputTab(), "Search");
          adapter.addFragment(new ProfileTab(), "Profile");
          adapter.addFragment(new GithubTab(), "Github Repos");
          adapter.addFragment(new FollowerTab(), "Followers");
          adapter.addFragment(new FollowingTab(), "Followings");
          adapter.addFragment(new UserSearchResultTab(), "test");
          viewPager.setAdapter(adapter);
      }
  
      @Override
      public void sendDataToProfile(String message) {
          String tag = "android:switcher:" + R.id.container + ":" + 1;
          ProfileTab profile = (ProfileTab) getSupportFragmentManager().findFragmentByTag(tag);
          profile.displayReceivedData(message);
      }
  
      @Override
     public void sendDataToFollowers(String message) {
         String tag = "android:switcher:" + R.id.container + ":" + 3;
         FollowerTab follower = (FollowerTab) getSupportFragmentManager().findFragmentByTag(tag);
         follower.displayReceivedData(message);
     }
  </code></pre>
  
  <p>The data successfully passes in to the <code>profileTab</code>, but when I debug it, it gives me <code>null</code> for other tabs like</p>
  
  <pre><code>FollowerTab follower = (FollowerTab) getSupportFragmentManager().findFragmentByTag(tag);
  </code></pre>
  
  <p>This one. Thus, it gives me a crash whenever I try to send a data to <code>FollowerTab</code>.</p>
  
  <p>What am I missing and how can I make it to become a non-null <code>fragment</code>?</p>