Refresh overlay object in Map Activity on Android

Question

I have to build a map activity and on top of that, I need to display some location points. These locations are retrieving from a hashtable in another class. The content of this hashtable always changes. So I expect to see those location spots on the Map Activity move as the hashtable is modified. The code is shown below:

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.mapview);

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


    mc.animateTo(...);
    mc.setZoom(12); 

    mapView.invalidate();

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

    MarkerOverlay mark = new MarkerOverlay(p);
     listOfOverlays.add(mark);

    for(Entry<Long,Pair> p: LQTManager.getInstance().ResultTable.entrySet())
    {

        GeoPoint point = new GeoPoint(
                    (int) (p.getValue().x * 1E6), 
                    (int) (p.getValue().y * 1E6));//some code is not shown
         MarkerOverlay markerOverlay = new MarkerOverlay(point);
         listOfOverlays.add(markerOverlay); 



    }

    mapView.postInvalidate();


}


class MarkerOverlay extends com.google.android.maps.Overlay
{
    public GeoPoint pt;

    public MarkerOverlay(GeoPoint pt){
        this.pt=pt;
        }

    @Override
    public boolean draw(Canvas canvas, MapView mapView, 
    boolean shadow, long when) 
    {
        super.draw(canvas, mapView, shadow);                   

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

        Bitmap bmp = BitmapFactory.decodeResource(
            getResources(), R.drawable.pushpin);            

        canvas.drawBitmap(bmp, screenPts.x-16, screenPts.y-32, null); 

        return true;
    }
} 

Is there any way to refresh overlay objects if I touch the screen. I am thinking about put some functions in onTap override method of MarkerOverlay. But I think is is not logically if I try to make the Overlay try to clear itself? Any suggested idea?

Solution 1

mapView.postInvalidate() will update the map view and redraw the overlays. I'm using this with a Runnable to refresh my overlays every second:

private Handler handler = new Handler();

private Runnable refreshTask = new Runnable()
{
  public void run()
  {
    handler.removeCallbacks(this);

    mapView.postInvalidate();

    handler.postDelayed(this, 1000);

  }
};

Solution 2

That might not be perfect but it worked for me, you may move the map a bit forth and back, which updates all overlays afterwards.

mapView.getController().scrollBy(1, 1);
mapView.getController().scrollBy(-1, -1);

Comments

[Martin]

I think that only applies to ItemizedOvelays. Aladine is overriding Overlay directly.

[Martin]

Surely that will jitter the display on lower dpi devices?

[Martin]

Perfect - thanks. @hectichavana - If you don't want periodic updates, just call mapView.postInvalidate() directly, and ignore all the Runnable stuff. For the periodic updates, see developer.android.com/reference/android/os/Handler.html.

[joecks]

Yes it will, so I would recommend the answer of filitchp!