New Post: where data.SelectedReminder is defined..

var viewModel = new ReminderDetailsViewModel
            {
                VehicleList = new VehicleListViewModel(vehicles, vehicle.VehicleId) { IsCollapsed = true },
                Reminder = ToFormModel(reminders.FirstOrDefault()),
                Reminders = new SelectedItemList<ReminderSummaryModel>(list, Enumerable.FirstOrDefault),
            };

public SelectedItemList(IEnumerable<T> source, T selectedItem)
        {
            List = source;
            SelectedItem = selectedItem;
        }