在OSM Androidf中聚焦标记

Question

我尝试使用自定义Overlay类为OSMdroid地图制作自定义标记。我在OSM中有自定义类标记。我想通过更改此标记的图标来显示聚焦标记。我该怎么办？

import android.app.AlertDialog;
import android.content.Context;
import android.graphics.Point;
import android.graphics.drawable.Drawable;

import org.osmdroid.ResourceProxy;
import org.osmdroid.api.IMapView;
import org.osmdroid.util.GeoPoint;
import org.osmdroid.views.overlay.ItemizedOverlay;
import org.osmdroid.views.overlay.OverlayItem;

import java.util.ArrayList;

public class MyItemizedOverlay extends ItemizedOverlay<OverlayItem> {

    private ArrayList<OverlayItem> overlayItemList = new ArrayList<OverlayItem>();
    private Context context;

    public MyItemizedOverlay(Drawable pDefaultMarker,
                             ResourceProxy pResourceProxy,Context context) {
        super(pDefaultMarker, pResourceProxy);
        this.context=context;
        // TODO Auto-generated constructor stub
    }

    public int addItem(GeoPoint p, String title, String snippet){
        OverlayItem newItem = new OverlayItem(title, snippet, p);
        overlayItemList.add(newItem);
        populate();
        return overlayItemList.size()-1;
    }

    @Override
    public boolean onSnapToItem(int arg0, int arg1, Point arg2, IMapView arg3) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    protected OverlayItem createItem(int arg0) {
        // TODO Auto-generated method stub
        return overlayItemList.get(arg0);
    }

    @Override
    public int size() {
        // TODO Auto-generated method stub
        return overlayItemList.size();
    }
    @Override
    protected boolean onTap(int index) {
        OverlayItem item = overlayItemList.get(index);
        AlertDialog.Builder dialog = new AlertDialog.Builder(context);
        dialog.setTitle(item.getTitle());
        dialog.setMessage(item.getSnippet());
        dialog.show();
        return true;
    }
}