emulator only shows one marker

i am trying to put a new marker everytime the user touches the screen. the following is my code, my problem is that the new marker doesn't appear at all

package com.org;

import java.io.IOException;
import java.util.List;
import java.util.Locale;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Point;
import android.location.Address;
import android.location.Geocoder;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.Toast;

import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapActivity;
import com.google.android.maps.MapController;
import com.google.android.maps.MapView;
import com.google.android.maps.MyLocationOverlay;
import com.google.android.maps.MapView.LayoutParams;
import com.google.android.maps.Overlay;

public class MapExampleActivity extends MapActivity {
MapView mapView;
MapController mc;
GeoPoint p;
MapOverlay mapOverlay = new MapOverlay();
private MyLocationOverlay myLocOverlay;

class MapOverlay extends com.google.android.maps.Overlay {
    @Override
    public boolean draw(Canvas canvas, MapView mapView, boolean shadow,
            long when) {
        super.draw(canvas, mapView, shadow);

        // ---translate the GeoPoint to screen pixels---
        Point screenPts = new Point();
        mapView.getProjection().toPixels(p, screenPts);

        // ---add the marker---
        Bitmap bmp = BitmapFactory.decodeResource(getResources(),
                R.drawable.marker);
        canvas.drawBitmap(bmp, screenPts.x + 25, screenPts.y - 50,null);
        return true;
    }
}


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


            mapView = (MapView) findViewById(R.id.mymap);
     LinearLayout zoomLayout = (LinearLayout)findViewById  (R.id.myzoom);  
            View zoomView = mapView.getZoomControls(); 

            zoomLayout.addView(zoomView, 
                new LinearLayout.LayoutParams(
                    LayoutParams.WRAP_CONTENT, 
                    LayoutParams.WRAP_CONTENT)); 
            mapView.displayZoomControls(true);

            mc = mapView.getController();
            String coordinates[] = {"1.352566007", "103.78921587"};
            double lat = Double.parseDouble(coordinates[0]);
            double lng = Double.parseDouble(coordinates[1]);

            p = new GeoPoint(
                (int) (lat * 1E6), 
                (int) (lng * 1E6));

            mc.animateTo(p)开发者_如何学编程;
            mc.setZoom(17); 


    // ---Add a location marker---
    MapOverlay mapOverlay = new MapOverlay();
    List<Overlay> listOfOverlays = mapView.getOverlays();
    listOfOverlays.clear();
    listOfOverlays.add(mapOverlay);

    mapView.invalidate();

}


@Override
protected boolean isRouteDisplayed() {
    // TODO Auto-generated method stub
    return false;
}
public boolean onTouchEvent(MotionEvent event, MapView mapView) 
     {   
     //---when user lifts his finger---
     if (event.getAction() == 1) {                
          GeoPoint p1 = mapView.getProjection().fromPixels(
             (int) event.getX(),
             (int) event.getY());


                 mc.animateTo(p1);
                 mc.setCenter(p1);
                 return true;
     }                            
     else 
         return false;
  }        


  }

Try this one. Replace your overlay onDraw() method with this one:

@Override
public boolean draw(Canvas canvas, MapView mapView, boolean shadow, long when) {
super.draw(canvas, mapView, shadow);    
Point screenPts = new Point();
mapView.getProjection().toPixels(p, screenPts);
for(int i=0;i<markerList.size();i++) {
    canvas.drawBitmapbmp(markerList.get(i), screenPts.x + 25, screenPts.y - 50,null);
}
   return false;
}

and add this method to your overlay class and also create a markerList at the top of your overlay class.

public boolean onTap(GeoPoint p, MapView map) {

Point screenPts = new Point();
mapView.getProjection().toPixels(p, screenPts);

// ---add the marker---
Bitmap bmp = BitmapFactory.decodeResource(getResources(),R.drawable.marker);
markerList.add(bmp);
return true;            
}