title: Prevent last Fragment from being removed from backstack
body: <p>I am currently writing a drawer layout as my main layout, with an embedded FrameLayout that I will be using to hold each “page” when an item on the drawer is clicked on. When the app first starts, an initial fragment will be show. Other fragments may be added/replaced later which is fine, however, my problem is that when the user clicks the back button on the very first “initial fragment”, I don’t want that particular fragment to be removed from the layout. Currently, it is being removed and it’s just showing a drawer layout with no other content (which makes sense). I want the app to automatically exit if the initial fragment was the last one showing and the back button is pressed, instead of removing that initial fragment and then after another back press, then it exits.</p>
  
  <p>Things I have thought of doing:</p>
  
  <ul>
  <li>Not adding the first fragment to the backstack.  (If I do this, I can compare it with the classname of the fragment which is a somewhat longer string, or I can use a boolean value for once the first fragment has been placed (and not added to backstack), the boolean is set which allows the fragments to now be added.</li>
  <li>Overriding the onBackPressed function of the activity</li>
  </ul>
  
  <p>Does anyone have a suggested way of doing this or can think of a better way? Thanks</p>