标记没有出现在Android谷歌地图上

Question

我正在尝试使用Android Studio向Android Google Maps API添加标记。当我运行时它不显示制造商，也不会放大区域。

import android.support.v4.app.FragmentActivity;
import android.os.Bundle;

import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;


public class MapWindow extends FragmentActivity implements OnMapReadyCallback {

    private GoogleMap mMap;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_map_window);
        MapFragment mapFragment = (MapFragment) getFragmentManager().findFragmentById(R.id.map);
        mapFragment.getMapAsync(MapWindow.this);
    }

    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        LatLng sydney = new LatLng(-34, 151);
        mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
        mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
    }
}