Question

I am trying to display a polygon on a mapview in android. I have created a custom overlay class(polygon) and overridden the draw method. After adding an instance of polygon to the mapview’s overlay list a polygon “should” be displayed. But when the map is displayed, there is no overlay to be found. What am I missing? Here is the main map activity where the polygon is created:

public class GPSLocator extends MapActivity {
MapView mapView;
Polygon polygon;

@Override
protected boolean isRouteDisplayed() {
    return false;
}

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mapView = (MapView) findViewById(R.id.mapview);
    mapView.setBuiltInZoomControls(true);

    ArrayList<GeoPoint> points = new ArrayList<GeoPoint>();
    points.add(new GeoPoint((int)(-86.63283601665323*1e6), (int)(34.6857467079488*1e6)));
    points.add(new GeoPoint((int)(-86.63172145427183*1e6), (int)(34.68572865382659*1e6))); 
    points.add(new GeoPoint((int)(-86.63172141228351*1e6), (int)(34.68613493108094*1e6))); 
    points.add(new GeoPoint((int)(-86.63288804303616*1e6), (int)(34.68611093719812*1e6)));     
    polygon = new Polygon(points);

    mapView.getOverlays().clear();
    mapView.getOverlays().add(polygon);
    mapView.invalidate();
}

And here is the custom overlay Polygon:

public class Polygon extends Overlay {

ArrayList<GeoPoint> geoPoints;

public Polygon(ArrayList<GeoPoint> points)
{
    geoPoints = points;
}

@Override
public void draw(Canvas canvas, MapView mapView, boolean shadow)
{
    //Set the color and style
    Paint paint = new Paint();
    paint.setColor(Color.RED);
        paint.setStyle(Paint.Style.FILL_AND_STROKE);

    //Create path and add points
    Path path = new Path();
    Point firstPoint = new Point();
    mapView.getProjection().toPixels(geoPoints.get(0), firstPoint);
    path.moveTo(firstPoint.x, firstPoint.y);

    for(int i = 1; i < geoPoints.size(); ++i)
    {
        Point nextPoint = new Point();
        mapView.getProjection().toPixels(geoPoints.get(i), nextPoint);
        path.lineTo(nextPoint.x, nextPoint.y);
    }

    //Close polygon
    path.lineTo(firstPoint.x, firstPoint.y);
    path.setLastPoint(firstPoint.x, firstPoint.y);
    canvas.drawPath(path, paint);
    super.draw(canvas, mapView, shadow);

}
}

Answer 1

You have to use path.moveTo(pixelPoint.x, pixelPoint.y); in your drawing loop. Otherwise you will draw a star not a polygon. Here is my (working) code for similar task:

public void draw(Canvas canvas, MapView mapv, boolean shadow) {
        super.draw(canvas, mapv, shadow);
        Log.i("BikeComputer", "MyOverlay draw");
        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(5);

        Point p1 = new Point();
        path = new Path();

        GeoPoint point = geoPoints.get(0);
        mapv.getProjection().toPixels(point, p1);
        path.moveTo(p1.x, p1.y);

        Point pixelPoint = new Point();
        Iterator<GeoPoint> i = geoPoints.iterator();
        while (i.hasNext()) {

            GeoPoint trackPoint = i.next();
            mapv.getProjection().toPixels(trackPoint, pixelPoint);
            path.lineTo(pixelPoint.x, pixelPoint.y);
            path.moveTo(pixelPoint.x, pixelPoint.y);
        }
        // draw track
        canvas.drawPath(path, mPaint);

        // start point
        mapv.getProjection().toPixels(geoPoints.get(0), pixelPoint);
        canvas.drawBitmap(startFlag, pixelPoint.x, pixelPoint.y - 32, null);

        // finish point

        mapv.getProjection().toPixels(geoPoints.get(geoPoints.size() - 1),
                pixelPoint);
        canvas.drawBitmap(finishFlag, pixelPoint.x, pixelPoint.y - 32, null);
    }

}

and how is this this class instaniazed:

        mapView = (MapView) findViewById(R.id.mapview);
    mapView.setBuiltInZoomControls(true);

    mapOverlays = mapView.getOverlays();
    mapView.getProjection();
    mapOverlays.add(new MyOverlay());