MainActivity.java

public class MainActivity extends android.support.v4.app.FragmentActivity {
	// Only one MapView instance is allowed per MapActivity,
	// so we inflate it in the MainActivity and tie its
	// lifetime here to the MainActivity.  Package scope
	// so we can grab them from different instances of map 
	// fragments.
	//
	// The other option was to make them static, but that causes
	// memory leaks on screen rotation.
	View mMapViewContainer;
	MapView mMapView;
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);

		// only init fragment the first time onCreate() is called.  Even if the Activity is
		// killed / recreated, FragmentManager will add the Fragment once the Activity is back.
		if( null == savedInstanceState ) {
			// do not add to backstack, or user will be able to press back and
			// view MainActivity's blank layout with nothing in it.
			// In this case, we want the back button to exit the app.
			getSupportFragmentManager()
				.beginTransaction()
				.add( R.id.main_layout, MyMapFragment.newInstance() )
				.setTransition( FragmentTransaction.TRANSIT_FRAGMENT_FADE )
				.commit();
		}
		
		mMapViewContainer = LayoutInflater.from( this ).inflate( R.layout.mapview, null );
		mMapView = (MapView)mMapViewContainer.findViewById( R.id.map );
	}
}

MyMapFragment.java

public class MyMapFragment extends Fragment {
	private View mMapViewContainer;
	private MapView mMapView;

	public static MyMapFragment newInstance() {
		MyMapFragment fragment = new MyMapFragment();

		Bundle args = new Bundle();
		// add any necessary args here
		fragment.setArguments( args );

		return fragment;
	}
	
	@Override
	public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
		super.onCreateView( inflater, container, savedInstanceState );

		// We can't grab the MapView onCreate() since Fragment#onCreate() is 
		// called before Activity#onCreate() (where the MapView is created).
		// We also can't do it in Fragment#onActivityCreated() since its called 
		// after Fragment#onCreateView().  So, we grab it every time here.
		//
		// Yes, its ugly that this fragment has to know that it lives inside
		// a MainActivity.
		MainActivity mainActivity = (MainActivity) getActivity();
		mMapViewContainer = mainActivity.mMapViewContainer;
		mMapView = mainActivity.mMapView;
	}

	// your other fragment code
}