random

public class MapFragmentOne extends Fragment implements OnMapReadyCallback,
        GoogleMap.OnMapClickListener {
    private static final int LAYOUT = R.layout.tab_one;
    private static View view;
    private static GoogleMap mMap;
    private SupportMapFragment mapFragment;
    private OnGetMap listener;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        LayoutInflater lf = getActivity().getLayoutInflater();
        view = lf.inflate(LAYOUT, container, false);

        mapFragment = (SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map);
        if (mapFragment == null) {
            FragmentManager fragmentManager = getFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            mapFragment = SupportMapFragment.newInstance();
            fragmentTransaction.replace(R.id.map, mapFragment).commit();
        }
        mapFragment.getMapAsync(this);
        return view;
    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        // А вот здесь не null
        Log.d("MAP2", mMap + "");
        mMap.getUiSettings().setZoomControlsEnabled(true);
        mMap.setBuildingsEnabled(true);
        mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
        mMap.setIndoorEnabled(true);
        mMap.setOnMapClickListener(this);
        if (listener != null) {
            listener.onGetMap(mMap);
        }
    }

    @Override
    public void onMapClick(LatLng point) {
        if (mMap != null) {
            //Actions on clicks
        }
    }

    public void getMap(OnGetMap listener) {
        if (mMap != null) {
            listener.onGetMap(mMap);
        } else {
            this.listener = listener;
        }
    }

    public interface OnGetMap {
        void onGetMap(GoogleMap map);
    }
}

mapFragmentOne.getMap(new OnGetMap() {
            @Override
            public void onGetMap(GoogleMap map) {
                // do something with map
            }
        });

Form2 f2 = new Form2();
if (f2.ShowDialog() == DialogResult.OK)
{
  TextBox1.Text = "ok";
}
else 
{
  TextBox1.Text = "";
}

private void Cancel_Click(object sender, EventArgs e)
{
  dialogResult = DialogResult.Cancel;
  Close();
}

private void OK_Click(object sender, EventArgs e)
{
  dialogResult = DialogResult.OK;
  Close();
}