public Envelope Extent {get;}

public Task<bool> ExpandExtentAsync(double dx, double dy)
{
  return QueuedTask.Run(() =>
  {
    //Get the active map view.
    var mapView = MapView.Active;
    if (mapView == null)
      return false;

    //Expand the current extent by the given ratio.
    var extent = mapView.Extent;
    var newExtent = ArcGIS.Core.Geometry.GeometryEngine.Instance.Expand(extent, dx, dy, true);
    return mapView.ZoomTo(newExtent);
  });
}