如何在Android Java中的SINGLETON模式下初始化Google Maps API v2？

Question

我想创建一个搜索预定义标记并在地图上显示的应用。我试图使用MVC，SINGLETON和CALLBACK模式。我在单例中创建了一个方法，它将在地图上显示标记：

问题是它在尝试创建IconGenerator时会给我一个NullPointerException。是否有可能在这里创建地图？我看到主要活动扩展了FragmentActivity并实现了OnMapReadyCallback。

public class Controller {
GoogleMap mMap;

private Controller() {
}

public static Controller getInstance() {
    return new Controller();
}


public Map<String, List<Marker>> adaugaRuta(ShowTheRute theRoute) {
    Map<String, List<Marker>> objectMap = new HashMap<>();

    Context context = MapsActivity.getAppContext();

    IconGenerator iconita = new IconGenerator(context);
    iconita.setContentPadding(5, -5, 5, -5);
    iconita.setRotation(-270);
    iconita.setContentRotation(270);

    Bitmap iconbit = iconita.makeIcon("test2");
    final Marker mae = mMap.addMarker(new MarkerOptions().icon(BitmapDescriptorFactory.fromBitmap(iconbit)).position(new LatLng(46.762035, 23.597659)).anchor(0f, 0.5f));
    mae.isVisible();

    List<Marker> marker1 = new ArrayList<>();
    marker1.add(mae);
    objectMap.put("UK", marker1);
    theRoute.getTheRute(objectMap);
    return objectMap;
}}

界面是：

public interface ShowTheRute {
void getTheRute(Map<String, List<Marker>> rute);}

主要活动是：

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback, ShowTheRute {

private GoogleMap mMap;
private static Context appContext;
private ArrayList<Polyline> mPolyline;
AutoCompleteTextView autoCompleteTextView;
Map<String, List<Marker>> mObjectMap = new HashMap<>();

String countries[] = {"INDIA", "ITALY", "JAPAN", "USA", "ICELAND",
        "INDONESIA", "UK", "IRAN", "IRAQ"};
ArrayAdapter<String> adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_maps);
    appContext=this;

    // Obtain the SupportMapFragment and get notified when the map is ready to be used.
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);


    autoCompleteTextView = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView1);
    autoCompleteTextView.setThreshold(1);
    adapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, countries);
    autoCompleteTextView.setAdapter(adapter);
    Controller.getInstance().adaugaRuta(MapsActivity.this);
    autoCompleteTextView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            String s = parent.getItemAtPosition(position).toString();
            if (s.equals("INDIA")) {
                PolylineOptions ruta1 = new PolylineOptions()
                        .add(new LatLng(46.760464, 23.561524))
                        .add(new LatLng(46.760795, 23.564249))
                        .add(new LatLng(46.761853, 23.568144))
                        .add(new LatLng(46.763139, 23.572757))
                        .add(new LatLng(46.764719, 23.575010))
                        .add(new LatLng(46.767137, 23.581737))
                        .add(new LatLng(46.770459, 23.588861))
                        .add(new LatLng(46.774594, 23.587409))
                        .add(new LatLng(46.774594, 23.587409));
                Polyline polyline = mMap.addPolyline(ruta1);


            } else for (String key : mObjectMap.keySet()) {
                if (s.equals(key)) {
                    mMap.clear();
                    PolylineOptions ruta1 = new PolylineOptions()
                            .add(new LatLng(46.756706, 23.597723))
                            .add(new LatLng(46.762035, 23.597659))
                            .add(new LatLng(46.766731, 23.598421))
                            .add(new LatLng(46.772441, 23.595556));
                    Polyline polyline1 = mMap.addPolyline(ruta1);
                }

            } /*else {
                Toast toast = Toast.makeText(getApplicationContext(), s + " is clicked", Toast.LENGTH_SHORT);
                toast.setGravity(Gravity.CENTER, 0, 0);
                toast.show();
            }*/
        }
    });
}
public static Context getAppContext() {
    return appContext;
}

@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;

    LatLng medias = new LatLng(46.767108, 23.581757);
    mMap.addMarker(new MarkerOptions().position(medias).title("medias"));
    mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(medias, 9));
    mMap.setMyLocationEnabled(true);
}
@Override
public void getTheRute(Map<String, List<Marker>> rute) {
    mObjectMap.putAll(rute);
}

}