Passing a null value to a DateTime property

[Mark Rae]

Hi,

I have a class with several properties, one of which is of the DateTime
datatype. However, this property will not always have a value, and I need to
check later whether it has a value or not.

When I create a new instance of the class, this property acquires a default
value of {1/1/1}, which I don't want at all, as that is a perfectly valid
date.

Is there any way to cause a DateTime datatype to have no value at all, which
I can check later?

Or is the answer not to use a DataTime datatype and use a generic object
datatype instead?

Any assistance gratefully received.

Mark

 

[Carlos J. Quintero [.NET MVP]]

Dates are value types, not reference types, so they can not be null, they
hold always a value. Could you use DateTime.MinValue as a special value to
denote no value?

--

Best regards,

Carlos J. Quintero

MZ-Tools: Productivity add-ins for Visual Studio .NET, VB6, VB5 and VBA
You can code, design and document much faster.
Free resources for add-in developers:
http://www.mztools.com

 

[Nicholas Paldino [.NET/C# MVP]]

Mark,

In .NET 2.0, you would use the Nullable<T>, with the type parameter T
equal to DateTime. This will produce a structure which has a HasValue
property which is true if there is a value, false if it is null.

If you are using a version of .NET before 2.0, then you could use the
SqlDateTime, which supports null semantics.

Hope this helps.

 

[Mark Rae]

Could you use DateTime.MinValue as a special value to denote no value?

Possibly - thanks for the answer.

 

[Mark Rae]

In .NET 2.0, you would use the Nullable<T>, with the type parameter T
equal to DateTime. This will produce a structure which has a HasValue
property which is true if there is a value, false if it is null.

Still using v1.1

If you are using a version of .NET before 2.0, then you could use the
SqlDateTime, which supports null semantics.

I'll try that - thanks.

 

[Guest]

You could also write your own class containing a DateTime that would then be
nullable. This might be easier than having to reference System.Data to use
SqlDateTime.

class MyDateTime
{
public MyDateTime(DateTime dt) { this._dt = dt; }

private DateTime _dt;

public DateTime Value { get { return this._dt; } }
};

 

[Mark Rae]

You could also write your own class containing a DateTime that would then
be
nullable. This might be easier than having to reference System.Data to use
SqlDateTime.

class MyDateTime
{
public MyDateTime(DateTime dt) { this._dt = dt; }

private DateTime _dt;

public DateTime Value { get { return this._dt; } }
};

Hmm - that looks rather good! Thanks very much

 

[Chris Dunaway]

Just for completeness, C# also allows declaring a nullable type like
this:

int? NullableInteger;

The ? denotes a nullable type.

VB does not have a similar syntax.

 

[Mark Rae]

Just for completeness, C# also allows declaring a nullable type like
this:

int? NullableInteger;

The ? denotes a nullable type.

VB does not have a similar syntax.

Interesting - could I apply that here...?

public class CSecurityClassn
{
private DateTime pMaturityDate;
public DateTime MaturityDate
{
get {return pMaturityDate;}
set {pMaturityDate = value;}
}
}

 

[Chris Dunaway]

This applies only to VC#.2005

 

[Chris Dunaway]

If this were VS.2005 then you wouldn't need a special class. You could
just do this:

DateTime? pNullableDate;

if pNullableDate.HasValue .....

 

[Mark Rae]

This applies only to VC#.2005

That's what I thought. I've been using 2005 for a while now at home, but
none of my clients is willing to upgrade to a beta product, unsurprisingly!