问安卓MapView内存使用率高的原因

EN

public class DetailMapTab extends MapActivity{
private MapView map=null;
private MyLocationOverlay me=null;
private SitesOverlay sites=null;
String placename;
int position;
String lat;
String lon;
ArrayList<HashMap<String, String>> mylist =new ArrayList<HashMap<String, String>>();


@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mapdetail);


//position -> is the selected record of the list 
//mylist -> contains record sets to display like name , lat and lon of various location
placename=mylist.get(position).get("Name");
lat=mylist.get(position).get("Latitude");
lon=mylist.get(position).get("Longitude");





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

map.getController().setCenter(getPoint(Double.valueOf(lat),Double.valueOf(lon)));

map.getController().setZoom(17);
map.setBuiltInZoomControls(true);

sites=new SitesOverlay();
map.getOverlays().add(sites);

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




}//oncreate

@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) {

        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 List<CustomItem> items=new ArrayList<CustomItem>();


    public SitesOverlay() {
        super(null);

        //show selected record geo-point with a new map pin1

        items.add(new CustomItem(getPoint(Double.valueOf(lat),Double.valueOf(lon))," ", placename,getMarker(R.drawable.pin1)));



          //show the geo-points names with pin2

            for(int i=0;i<mylist.size();i++)
            {


                if(position!=i)
                {

                items.add(new CustomItem(getPoint(Double.valueOf(mylist.get(i).get("Latitude")),Double.valueOf(mylist.get(i).get("Longitude"))),"",mylist.get(i).get("Name"),getMarker(R.drawable.pin2)));
                }
            }
        }

    }
    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);
        Toast.makeText(getApplicationContext(),items.get(i).getSnippet(),Toast.LENGTH_SHORT).show();
        return(true);
    }

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



    private Drawable getMarker(int resource) {
        Drawable marker=getResources().getDrawable(resource);

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

        return(marker);
    }
}



 class CustomItem extends OverlayItem {
    Drawable marker=null;


    CustomItem(GeoPoint pt, String name, String snippet, Drawable marker) {
        super(pt, name, snippet);

        this.marker=marker;

    }

    @Override
    public Drawable getMarker(int stateBitset) {
        Drawable result= marker;

        setState(result, stateBitset);

        return(result);
    }


}


  public void onDestroy(){
         super.onDestroy();


        map=null;
        me=null;
        sites=null;

        gr=null;
        placename=null;
        lat=null;
        lon=null;
        mylist =null;
         System.gc();



     }
 }

 11-11 15:39:55.072: DEBUG/dalvikvm(222): GC freed 439 objects / 83360 bytes in 106ms
 11-11 15:39:56.052: DEBUG/dalvikvm(107): GC freed 3568 objects / 197464 bytes in 138ms
 11-11 15:39:57.451: DEBUG/dalvikvm(222): GC freed 135 objects / 41456 bytes in 101ms
 11-11 15:39:59.891: DEBUG/dalvikvm(222): GC freed 94 objects / 42112 bytes in 134ms
 11-11 15:44:27.481: DEBUG/dalvikvm(104): GC freed 7472 objects / 406240 bytes in 140ms