android - handle back button in single fragment -

i have application navigation drawer. when start application, have on main screen (screen a) "hello world" , when select item navigation drawer, load fragment , "new hello world" , again when select item navigation drawer, load fragment , "hello universe". since happening via 1 single fragment, when press device button should previous fragment below:

"hello universe" >press back> "new hello world" >press back> "hello world"

how handle ?

note:

while changing fragment have tried

fragmentmanager.begintransaction().replace(r.id.maincontent, fragment).commit(); 

then changed :

fragmentmanager.begintransaction().add(r.id.maincontent, fragment).addtobackstack("tag").commit(); 

but nothing worked. app exits on button press. due same fragment getting replaced content again , again?

the second approach tried correct.try call popbackstack() on backpressed() overriding onbackpressed() method.

 @override public void onbackpressed() {     if (getfragmentmanager().getbackstackentrycount() > 0) {         getfragmentmanager().popbackstack();     } else if (getfragmentmanager().getbackstackentrycount() == 0) {         super.onbackpressed();     } }