getSupportFragmentManager().findFragmentById retur

I have a problem with Google Maps, i.e. getSupportFragmentManager().findFragmentById returns always null. Do you have an idea how to solve this?

Here is the code:

fragment_map.xml:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.myapp.something.MapFragment">
<fragment
    android:id="@+id/map"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    class="com.google.android.gms.maps.SupportMapFragment" />                  
</FrameLayout>

MapsFragment.java:

public class MapFragment extends Fragment implements OnMapReadyCallback, android.location.LocationListener

public void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    SupportMapFragment mapFragment = (SupportMapFragment) this.getActivity().getSupportFragmentManager().findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);
...

I have Google Maps in Activity and it works with code:

SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);

I am trying to reuse this in fragment, becouse I need maps in fragment, not in activity, but it doesn't work.

I tried:

calling this code in "onCreateView" function
SupportMapFragment mapFragment = (SupportMapFragment) getFragmentManager().findFragmentById(R.id.map);
GoogleMap mGoogleMap = ((SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map)).getMap(); is deprecated, and application crashes
SupportMapFragment mapFragment = (SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map); and similar variations, but in all cases I get null for mapFragment.

Do you know how could I solve this problem?

The problem is that you're trying to use the Activity's FragmentManager, and you should be using the Fragment's child FragmentManager.

Remove the onCreate() override in the Fragment, and add an onCreateView() Override where you inflate the layout and call getMapAsync():

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.fragment_map, container, false);

    SupportMapFragment mapFragment = (SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map);

    mapFragment.getMapAsync(this);

    return rootView;
}