google map中施用多种图钉来标示地点

google map中使用多种图钉来标示地点
如题：要在google 地图中使用多种图钉来表示地点的不同状态,如红色图钉表示可用,黑色表示不可用等。找到一示例,是google论坛上的例子(http://groups.google.com/group/android-developers/browse_thread/thread/60666b7dae3f77b8)
源码如下：

public class NooYawk extends MapActivity {
  private MapView map=null;
  private MyLocationOverlay me=null;
  private SitesOverlay sites=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,
                                            -73.98180484771729));
    map.getController().setZoom(17);
    map.setBuiltInZoomControls(true);
    
    sites=new SitesOverlay();
    map.getOverlays().add(sites);
    
    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);
    }
    else if (keyCode == KeyEvent.KEYCODE_H) {
      sites.toggleHeart();
      
      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<CustomItem> {
    private Drawable heart=null;
    private List<CustomItem> items=new ArrayList<CustomItem>();
    private PopupPanel panel=new PopupPanel(R.layout.popup);
    
    public SitesOverlay() {
      super(null);
      
      heart=getMarker(R.drawable.heart_full);
      
      items.add(new CustomItem(getPoint(40.748963847316034,
                                          -73.96807193756104),
                                "UN", "United Nations",
                                getMarker(R.drawable.blue_full_marker),
                                heart));
      items.add(new CustomItem(getPoint(40.76866299974387,
                                          -73.98268461227417),
                                "Lincoln Center",
                                "Home of Jazz at Lincoln Center",
                                getMarker(R.drawable.orange_full_marker),
                                heart));
      items.add(new CustomItem(getPoint(40.765136435316755,
                                          -73.97989511489868),
                                "Carnegie Hall",
              "Where you go with practice, practice, practice",
                                getMarker(R.drawable.green_full_marker),
                                heart));
      items.add(new CustomItem(getPoint(40.70686417491799,
                                          -74.01572942733765),
                                "The Downtown Club",
                        "Original home of the Heisman Trophy",
                                getMarker(R.drawable.purple_full_marker),
                                heart));

      populate();
    }
    
    @Override
    protected CustomItem createItem(int i) {
      return(items.get(i));
    }
    
    @Override
    public void draw(Canvas canvas, MapView mapView,
                      boolean shadow) {
      super.draw(canvas, mapView, shadow);
      
    }
    
    @Override
    protected boolean onTap(int i) {
      OverlayItem item=getItem(i);
      GeoPoint geo=item.getPoint();
      Point pt=map.getProjection().toPixels(geo, null);
      
      View view=panel.getView();
      
      ((TextView)view.findViewById(R.id.latitude))
        .setText(String.valueOf(geo.getLatitudeE6()/1000000.0));
      ((TextView)view.findViewById(R.id.longitude))
        .setText(String.valueOf(geo.getLongitudeE6()/1000000.0));
      ((TextView)view.findViewById(R.id.x))
                              .setText(String.valueOf(pt.x));
      ((TextView)view.findViewById(R.id.y))
                              .setText(String.valueOf(pt.y));
      
      panel.show(pt.y*2>map.getHeight());
      
      return(true);
    }
    
    @Override
    public int size() {
      return(items.size());
    }
    
    void toggleHeart() {
      CustomItem focus=getFocus();
      
      if (focus!=null) {
        focus.toggleHeart();
      }
      
      map.invalidate();
    }
    
    private Drawable getMarker(int resource) {
      Drawable marker=getResources().getDrawable(resource);
      
      marker.setBounds(0, 0, marker.getIntrinsicWidth(),
                        marker.getIntrinsicHeight());
      boundCenter(marker);

      return(marker);
    }
  }
  
  class PopupPanel {
    View popup;
    boolean isVisible=false;
    
    PopupPanel(int layout) {
      ViewGroup parent=(ViewGroup)map.getParent();

      popup=getLayoutInflater().inflate(layout, parent, false);
                  
      popup.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
          hide();
        }
      });
    }
    
    View getView() {
      return(popup);
    }
    
    void show(boolean alignTop) {
      RelativeLayout.LayoutParams lp=new RelativeLayout.LayoutParams(
            RelativeLayout.LayoutParams.WRAP_CONTENT,
            RelativeLayout.LayoutParams.WRAP_CONTENT
      );
      
      if (alignTop) {
        lp.addRule(RelativeLayout.ALIGN_PARENT_TOP);
        lp.setMargins(0, 20, 0, 0);
      }
      else {
        lp.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM);
        lp.setMargins(0, 0, 0, 60);
      }
      
      hide();
      
      ((ViewGroup)map.getParent()).addView(popup, lp);
      isVisible=true;
    }
    
    void hide() {
      if (isVisible) {
        isVisible=false;
        ((ViewGroup)popup.getParent()).removeView(popup);
      }
    }
  }
  
  class CustomItem extends OverlayItem {
    Drawable marker=null;
    boolean isHeart=false;
    Drawable heart=null;
    
    CustomItem(GeoPoint pt, String name, String snippet,
               Drawable marker, Drawable heart) {
      super(pt, name, snippet);
      
      this.marker=marker;
      this.heart=heart;
    }
    
    @Override
    public Drawable getMarker(int stateBitset) {
      Drawable result=(isHeart ? heart : marker);
      
      setState(result, stateBitset);
    
      return(result);
    }
    
    void toggleHeart() {
      isHeart=!isHeart;
    }
  }
}

整个项目链接：https://github.com/commonsguy/cw-advandroid/tree/master/Maps/ILuvNooYawk