System.DateTime? vs System.DateTime

Question

I was writing to some code where I needed to read the date value from a Calendar control in my page (Ajax toolkit: calendar extender).

The code below:

Answer 1

? means that the type is nullable. For details, see e.g. MSDN

Nullable is a compiler-supported wrapper around value types that allows value types to become null.

To access the DateTime value, you need to do the following:

DateTime? dateOrNull = myCalendarExtender.SelectedDate;
if (dateOrNull != null)
{
    DateTime newSelectedDate = dateOrNull.Value;
}