void RefreshDistricts()
{
if (Region != null)
{
Districts = new ObservableCollection <District>(
(from district in Session.DataModel.Districts
where district.RegionId == Region.Id
orderby district.Name
select district));
}
else
{
Districts = new ObservableCollection <District>();
}
if (!Districts.Contains(District))
{
District = null;
}
}