可以为空的日期时间值

Question

Can a DateTime value be NULL ?

I have this code:

From here I inherit my variable

namespace Transakcija
{
     public class Line
     {
        public System.DateTime DateOfProduction { get; set; }
     }
}

Then for each loop:

foreach (var rw_det in dt_stavke.Rows)
{
    var list = new List<Transakcija.Line>();
    var l = new Transakcija.Line();

     //DateOfProduction
    if (rw_det["DPRO02"].ToString().Length <= 0)
    {
        l.DateOfProduction = default(DateTime);
    }
    else
    {
        l.DateOfProduction = new DateTime();
        prod_date = rw_det["DPRO02"].ToString();
        DateTime pro_date = DateTime.ParseExact(prod_date, "dd.MM.yyyy", CultureInfo.InvariantCulture);
        string p_date = pro_date.ToString("yyyy-MM-dd");
        l.DateOfProduction = DateTime.Parse(p_date);
    }
}

So the value l.DateOfProduction needs to be null. I have tried this:

DateTime? dt = null;
l.DateOfProduction = (DateTime)dt;

But I got error: nullable object must have a value

So is this possible or do I have to pass the minimum datetime value to the variable?

Answer 1

DateTime is a value type, so no it can never be null . If you need a "no value" value, use a Nullable<DateTime> or for short DateTime?

Answer 2

You can assigne a nullable DateTime by using the constructor :

DateTime? dt = new Nullable<DateTime>(); 

You can check if a nullable type is null by using the HasValue property:

if(dt.HasValue)
{
    // now you can safely use dt.Value as DateTime, 
    // otherwise accessing the Value property raises an InvalidOperationException
    DateTime otherDate = dt.Value;
}

Answer 3

yoe can have Dateime Nullable this way

DateTime? dtNullable = new Nullable<DateTime>(); 

if(dtNullable.HasValue)
 l.DateOfProduction = dtNullable.Value;

PS: example if you passing a non nullable DateTime to a Nullable DateTime then it will require casting

Like this

DateTime? nullableDateTime = (DateTime?)nonNullableDateTime;