How to check if DateTime is null

Question

I have my two DateTime as follow:

        DateTime startDate = CalendarFrom.SelectedDate;
        DateTime endDate = CalendarTo.SelectedDate;

Now, I want to check if the startDate and endDate is selected or not. As I know, we cannot assign null to DateTime so I write in this way:

       if (startDate == DateTime.MinValue && endDate == DateTime.MinValue)
       {
             // actions here
       }

However I realise that for the endDate, it is not "1/1/0001 12:00:00 AM" so it cannot be checked by using DateTime.MinValue.

I would like to know how will I be able to do checking for the endDate. Thanks!

Solution 1

A DateTime itself can't be null - it's cleanest to use DateTime? aka Nullable<DateTime> to represent nullable values.

It's not clear what CalendarFrom and CalendarTo are, but they may not support Nullable<DateTime> themselves - but it would be a good idea to centralize the conversion here so you can use Nullable<DateTime> everywhere other than where you're directly using CalendarFrom and CalendarTo.

Solution 2

DateTime is a struct and so it can never be null.

I can think of two options:

1. If you really want to support null, use DateTime? to create a nullable DateTime.

2. Alternatively, it may be appropriate in your application to simply set a DateTime value to a default value that indicates no real value has been set. For this default value, you could use either default(DateTime) or something like DateTime.MinValue.

Solution 3

I am not sure what are your CalenderFrom and CalenderTo are; but I am assuming that they are static classess. Based on that assumption, this is how I would write this code.

public static class CalendarFrom
{
    public static DateTime SelectedFrom { get; set; }
}

public static class CalendarTo
{
    public static DateTime SelectedDate { get; set; }
}

DateTime? startDate = CalendarFrom.SelectedFrom;
            DateTime? endDate = CalendarTo.SelectedDate;

            if (startDate.HasValue 
                && ( startDate.Value != DateTime.MaxValue || startDate.Value != DateTime.MinValue))
            {
            }