Is it possible (or advisable) to use Activity as switched component of ActionBar's navigation tab or drop-down navigation
<p>I have 2 Activities. One of it is displaying line chart, another is displaying pie chart. I would like to embed both in a single launched Activity. User is allowed to perform single click, to switch between line chart and pie chart.</p>

<p>I realize ActionBar's navigation tab, or drop-down navigation is the best candidate to help me achieve this purpose. </p>

<p>From Android API demo, and guideline found from <a href="http://developer.android.com/guide/topics/ui/actionbar.html" rel="nofollow">http://developer.android.com/guide/topics/ui/actionbar.html</a>, I realize all switched components are implemented as <code>Fragment</code>, not <code>Activity</code></p>

<ol>
<li>Does it mean that I need to port my previous 2 Activities into 2 Fragments, in order to embed them into ActionBar's tab navigation view/ drop-down navigation view?</li>
<li>Is there any other ways I can do without porting? But, is it advisable as I do not find an official example by using Activity.</li>
<li>In API demo, I realize most Fragment is implemented in the following pattern.</li>
</ol>

<hr>

<pre><code>public class FragmentStack extends Activity {
    ...
    public static class CountingFragment extends Fragment {
        // CountingFragment never access any members in FragmentStack
    }
}
</code></pre>

<p>Is there any reason to do so? Why don't they have <code>CountingFragment</code> is a separated file? </p>
