问Android地图显示蓝屏，而不是地图

EN

public class HelloGoogleMaps3 extends MapActivity {
    private MapView map=null;
    private MyLocationOverlay me=null;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        map=(MapView)findViewById(R.id.map);

        map.getController().setCenter(getPoint
                (40.76793169992044,-173.98180484771729));
        map.getController().setZoom(17);
        map.setBuiltInZoomControls(true);

        Drawable marker=getResources().getDrawable(R.drawable.marker);

        marker.setBounds(0, 0, marker.getIntrinsicWidth(),
                        marker.getIntrinsicHeight());

        map.getOverlays().add(new SitesOverlay(marker));

        me=new MyLocationOverlay(this, map);
        map.getOverlays().add(me);
    }

    @Override
    public void onResume() {
        super.onResume();

        me.enableCompass();
    }       

    @Override
    public void onPause() {
        super.onPause();

        me.disableCompass();
    }       

    @Override
    protected boolean isRouteDisplayed() {
        return(false);
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_S) {
            map.setSatellite(!map.isSatellite());
            return(true);
        }
        else if (keyCode == KeyEvent.KEYCODE_Z) {
            map.displayZoomControls(true);
            return(true);
        }

        return(super.onKeyDown(keyCode, event));
    }

    private GeoPoint getPoint(double lat, double lon) {
        return(new GeoPoint((int)(lat*1000000.0),
                            (int)(lon*1000000.0)));
    }

    private class SitesOverlay extends ItemizedOverlay<OverlayItem> {
        private List<OverlayItem> items=new ArrayList<OverlayItem>();
        private Drawable marker=null;

        public SitesOverlay(Drawable marker) {
            super(marker);
            this.marker=marker;

            items.add(new OverlayItem(getPoint
                    (40.748963847316034,-173.96807193756104),
                                "UN", "United Nations"));
            items.add(new OverlayItem(getPoint
                    (40.76866299974387,-173.98268461227417),
                                "Lincoln Center",
                                "Home of Jazz at Lincoln Center"));
            items.add(new OverlayItem(getPoint
                    (40.765136435316755,-173.97989511489868),
                                "Carnegie Hall",
                        "Where you go with practice, practice, practice"));
            items.add(new OverlayItem(getPoint
                    (40.70686417491799,-174.01572942733765),
                                "The Downtown Club",
                        "Original home of the Heisman Trophy"));

            populate();
        }

        @Override
        protected OverlayItem createItem(int i) {
            return(items.get(i));
        }

        @Override
        public void draw(Canvas canvas, MapView mapView,
                                        boolean shadow) {
            super.draw(canvas, mapView, shadow);

            boundCenterBottom(marker);
        }

        @Override
        protected boolean onTap(int i) {
            Toast.makeText(HelloGoogleMaps3.this,
                                items.get(i).getSnippet(),
                                Toast.LENGTH_SHORT).show();

            return(true);
        }

        @Override
        public int size() {
            return(items.size());
        }
    }
}