问MKPolygonView填充颜色属性不起作用

EN

- (MKOverlayView *)mapView:(MKMapView *)mapView viewForOverlay:(id )overlay
{
    NSLog(@"inside the viewForOverlay delegate");

    NSLog(@"draw polygon inside the viewForOverlay delegate");
    //for draw polygon---
    if ([overlay isKindOfClass:[MKPolygon class]]) {
        MKPolygonView* v = nil;
        v = [[[MKPolygonView alloc] initWithPolygon:(MKPolygon*)overlay]
             autorelease];

                v.lineWidth = 10;
                v.strokeColor = [[UIColor redColor] colorWithAlphaComponent:1];
                v.fillColor = [[UIColor greenColor] colorWithAlphaComponent:1];
        return v;
    }

    return nil;
}