title: Back button in fragment
body: <p>I have a navigation drawer and 8 fragment (one of which is my "main fragment"), selecting the item I select the fragment corresponding content in MainActiviy.
  When I am in one of the fragment and I press the back button the application closes, while I would like it closed only when it is in a specific fragment ("main fragment"), while when I am in the other must return to the "main fragment"
  How can I do this?
  Thanks in advance</p>