title: ActionBar Back Arrow/Button not appearing
body: <p>I am switching between my fragments using:</p>
  
  <pre><code>FragmentTransaction tx = getSupportFragmentManager().beginTransaction();
  tx.replace(R.id.main, Fragment.instantiate(MainActivity.this, fragments[pos]));
  tx.addToBackStack("tag");
  tx.commit();
  </code></pre>
  
  <p>But when I do switch fragments, the back button or left caret is not appearing on my action bar. I have set</p>
  
  <pre><code>getActionBar().setDisplayHomeAsUpEnabled(true);
  getActionBar().setHomeButtonEnabled(true);
  </code></pre>
  
  <p>on the main activity but still doesnt work.</p>
  
  <p>Am I placing the 2 previous lines of code in the wrong place or class? Or is it my navigation from fragment to another fragment that is not showing the left arrow/caret?</p>