How to check if DateTime object is null

Question

I'm looking to validate a DateTime variable to ensure that it isn't blank on the UI. The string equivalent checking would be String.IsNullOrEmpty(), but how would I go about it with my DateTime variable?

Solution 1

DateTime is a value type, so it cannot be null. To check if a DateTime variable has the default (all 0) value you can compare it with new DateTime() or default(DateTime).

Another option would be to use DateTime? instead of DateTime for user input and check HasValue property.

Solution 2

To check if a DateTime is null in C#, you must first ensure the DateTime is nullable.

// DateTime? means it is nullable
var DateTime? date = null;

// .HasValue only exists if DateTime is nullable
if(date.HasValue)
    Console.WriteLine("date has a value");
else
    Console.WriteLine("date is null");

If your DateTime is not nullable, make it nullable (unless you are absolutely certain in will never be null). You don't want to go down the road of assigning "nullish" values to your DateTimes. In my experience, this creates confusing bugs / code.