reopen Google map stops my Application - google-maps

Question

i have tow fragment. by click in first fragment button second fragment that is Google map will open.
first time all thing is correct but if i back and click again program will stop.
map fragment code is as blow:
public class map extends Fragment implements OnMapReadyCallback {
private GoogleMap mMap;
private double lat;
private double att;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view=inflater.inflate(R.layout.map,container,false);
// GoogleMap map = ((MapFragment) getFragmentManager(.findFragmentById(R.id.map)).getMap();
return view;
}
#Override
public void onStart() {
super.onStart();
if (getArguments() != null) {
lat= getArguments().getDouble("LAT");
att=getArguments().getDouble("ATT");
Toast.makeText(getActivity(),String.valueOf(att),Toast.LENGTH_LONG).show();
MapFragment mapFragment = (MapFragment) getFragmentManager().findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
}
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
}
#Override
public void onMapReady(GoogleMap googleMap) {
// Add a marker in Sydney and move the camera
LatLng sydney = new LatLng(lat, att);
CameraPosition googlePlex = CameraPosition.builder()
.target(new LatLng(lat,att))
.zoom(16).build();
googleMap.addMarker(new MarkerOptions().position(sydney));
googleMap.moveCamera(CameraUpdateFactory.newCameraPosition(googlePlex));
}
}
and main activity is:
public class MainActivity extends AppCompatActivity implements onclicklistener{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(findViewById(R.id.firstpage)!=null)
{
if(savedInstanceState!=null)
return;
firstpage startpage=new firstpage();
FragmentManager fm=getFragmentManager();
FragmentTransaction ft=fm.beginTransaction();
ft.add(R.id.firstpage,startpage);
ft.commit();
}
}
#Override
public void onclickbutton(String index) {
try{ map newmap=new map();
Bundle args = new Bundle();
args.putDouble("LAT",32.657892);
args.putDouble("ATT",51.668643);
FragmentManager fm=getFragmentManager();
FragmentTransaction ft=fm.beginTransaction();
newmap.setArguments(args);
ft.addToBackStack(null);
ft.replace(R.id.firstpage,newmap);
ft.commit();}
catch (Exception e){Toast toast = Toast.makeText(this, "error", Toast.LENGTH_SHORT);}
}
#Override
public void onBackPressed() {
if (getFragmentManager().getBackStackEntryCount() > 0 ){
getFragmentManager().popBackStack();
} else {
super.onBackPressed();
}
}
}
first Run is completely OK but if i click again program will stop. please guide me.

Answer 1

it solved.
i added this code:
#Override
public void onDetach() {
Fragment fragment = (getFragmentManager().findFragmentById(R.id.map));
FragmentTransaction ft = getActivity().getFragmentManager().beginTransaction();
ft.remove(fragment);
ft.commit();
super.onDetach();
}