android - Fragment onKeyDown() not working as intended -

i have framgments called in order fragone calls fragtest , fragtest calls fragbook. when current fragment fragbook on pressing button, fragtest shown split second , app sent app tray.

@override public boolean onkeydown(int keycode, keyevent event) {     fragmentmanager fragmanager = getsupportfragmentmanager();     fragment frag = fragmanager.findfragmentbytag("frag_book");      if ((keycode == keyevent.keycode_back)) {         if (frag.isvisible()) {             fragmanager.begintransaction()                     .replace(r.id.container, fragment.instantiate(mainactivity.this, fragments[1]),"frag_test")                     .commit();         }     }     return super.onkeydown(keycode, event); } 

where have gone wrong in approach? thanks...

    @override     public boolean onkeydown(int keycode, keyevent event) {         fragmentmanager fragmanager = getsupportfragmentmanager();         fragment frag = fragmanager.findfragmentbytag("frag_book");          if ((keycode == keyevent.keycode_back)) {             if (frag.isvisible()) {                 fragmanager.begintransaction()                         .replace(r.id.container, fragment.instantiate(mainactivity.this, fragments[1]),"frag_test")                         .commit();              return true; //"------------- should add"             }         }         return super.onkeydown(keycode, event);     }