I wanted to assign null value to DateTime type in c#, so I used:
public DateTime? LockTime;
When LockTime is not assigned LockTime.Value contains null by default. I want to be able to change LockTime.Value to null after it has been assigned other value.
No, if LockTime hasn't been assigned a value, it will be the nullable value by default - so LockTime.Value will throw an exception if you try to access it.
You can't assign null to LockTime.Value itself, firstly because it's read-only and secondly because the type of LockTime.Value is the non-nullable DateTime type.
However, you can set the value of the variable to be the null value in several different ways:
LockTime = null; // Probably the most idiomatic way
LockTime = new DateTime?();
LockTime = default(DateTime?);
You could assign null directly to the variable (the Value property is readonly and it cannot be assigned a value):
LockTime = null;
Have you tried LockTime = null?
The Value porperty is readonly, so you can't assign a value to it. What you can do is to assign null to the LockTime field:
LockTime = null;
However, this will create a new DateTime? instance, so any other pieces of code having a reference to the original LockTime instance will not see this change. This is nothing strange, it's the same thing that would happen with a regular DateTime, so it's just something your code has to deal with gracefully.
DateTime? nullableDT = null;
Console.WriteLine("{0}\t{1}", nullableDT.HasValue, nullableDT);
nullableDT = DateTime.Now;
Console.WriteLine("{0}\t{1}", nullableDT.HasValue, nullableDT);
nullableDT = null;
Console.WriteLine("{0}\t{1}", nullableDT.HasValue, nullableDT);
/*
False
True 30.07.2010 11:17:59
False
*/
You can define the variable this way:
private Nullable<DateTime> _assignedDate;
_assignedDate = DateTime.Now;
and then assign a null value:
_assignedDate = null;
