draw lines between GPS coordinates

问题:

I want to track user's positions using GPS and draw lines between visited GPS points.

My code draw one time, then it doesn't draw

public class Test extends Activity {

    float lat1, lon1 = 0;
    float lat0, lon0 = 0;
    private LocationManager locManager;
    private LocationListener locListener;
    private MapController mc;
    private MapView mapView;
    private MyOverlay myoverlay;
    private Projection projection;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_tracklocation);

        mapView = (MapView) findViewById(R.id.map);
        mc = mapView.getController();
        mapView.setBuiltInZoomControls(true);

        locManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        locListener = new MylocListener();

        GeoPoint initGeoPoint = new GeoPoint((int) ( locManager.getLastKnownLocation(LocationManager.GPS_PROVIDER).getLatitude() * 1000000 ),
                (int) ( locManager.getLastKnownLocation(LocationManager.GPS_PROVIDER).getLongitude() * 1000000 ));

        Toast.makeText(getBaseContext(),
                "Initial Latitude: " + locManager.getLastKnownLocation(LocationManager.GPS_PROVIDER).getLatitude() * 1000000 +
                "Initial Longitude: " + locManager.getLastKnownLocation(LocationManager.GPS_PROVIDER).getLongitude() * 1000000,
                Toast.LENGTH_LONG).show();

        lat0 = (float) locManager.getLastKnownLocation(LocationManager.GPS_PROVIDER).getLatitude() * 1000000;
        lon0 = (float) locManager.getLastKnownLocation(LocationManager.GPS_PROVIDER).getLongitude() * 1000000;

        GeoPoint gPe = new GeoPoint((int) lat0, (int) lon0);//starting point Abbottabad

        mc.animateTo(gPe);
        mc.setZoom(16);

        locManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locListener);
    }

    public class MylocListener implements LocationListener {

        public void onLocationChanged(Location arg0) {
            GeoPoint gP2 = new GeoPoint(
                    (int) ( arg0.getLatitude() * 1E6 ),
                    (int) ( arg0.getLongitude() * 1E6 ));


            Toast.makeText(getBaseContext(),
                    "Latitude: " + arg0.getLatitude() +
                    " Longitude: " + arg0.getLongitude(),
                    Toast.LENGTH_LONG).show();

            lat1 = (float) gP2.getLatitudeE6() / 1000000;
            lon1 = (float) gP2.getLongitudeE6() / 1000000;

            MyOverlay mapOverlay = new MyOverlay();
            projection = mapView.getProjection();

            List<Overlay> listOfOverlays = mapView.getOverlays();
            listOfOverlays.clear();
            listOfOverlays.add(mapOverlay);

            mapView.invalidate();
        }

        public void onStatusChanged(String arg0, int arg1, Bundle arg2) {
        }

    }

    class MyOverlay extends Overlay {

        public MyOverlay() {
        }

        public void draw(Canvas canvas, MapView mapv, boolean shadow) {
            super.draw(canvas, mapv, shadow);
            //Configuring the paint brush
            Paint mPaint = new Paint();
            mPaint.setDither(true);
            mPaint.setColor(Color.RED);
            mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
            mPaint.setStrokeJoin(Paint.Join.ROUND);
            mPaint.setStrokeCap(Paint.Cap.ROUND);
            mPaint.setStrokeWidth(4);

            GeoPoint gPe = new GeoPoint((int) lat0, (int) lon0);//starting point Abbottabad
            GeoPoint gP2 = new GeoPoint((int) lat1, (int) lon1);//starting point Abbottabad

            Point p1 = new Point();
            Point p2 = new Point();
            Path path1 = new Path();

            projection.toPixels(gP2, p2);
            projection.toPixels(gPe, p1);

            mc.animateTo(gP2);

            path1.moveTo(p2.x, p2.y);//Moving to Islamabad location
            path1.lineTo(p1.x, p1.y);//Path to Rawalpindi

            canvas.drawPath(path1, mPaint);

            Toast.makeText(getBaseContext(),
                    "I've drawn" + (float) gP2.getLatitudeE6() / 1000000 +
                            (float) gP2.getLongitudeE6() / 1000000,
                    Toast.LENGTH_LONG).show();

            gPe = new GeoPoint((int) lat1, (int) lon1);
        }
    }
}