java - My app crashes when I press navigation item twice using map View -

this onnavigationitemselected method:

        } 

do this:

 int id = item.getitemid(); fragmenttransaction fragmenttransaction;      if (id == r.id.nav_sports) {          fragment = new fragmentone();       } else if (id == r.id.nav_food) {         fragment = new fragmenttwo();        } else if (id == r.id.nav_security) {         fragment = new fragmentthree();      } if (fragment != null) {                 fragmenttransaction = getsupportfragmentmanager().begintransaction();                 fragmenttransaction.replace(r.id.containerview, fragment).commit();             }