Using a System.DateTime type as optional parameter in Visual Basic VB.Net 2010

Question

I am trying to pass an optional System.DateTime parameter to a constructor in VB.NET 2010.

...
Public Sub New(Optional ByVal givendate As System.DateTime = System.DateTime.MinValue)
    ...

I am getting an error "Konstanter Ausdruck erforderlich" translating to "constant value required". I tried to fill a variable with the MinValue, but I have to make this variable readonly, which leads to exactly the same problem when trying to pass as default value to the optional parameter. Is there a way to pass the MinValue as default value to the optional DateTime (which is actually a Date type). Thank you for your audience.

Answer 1

Well I found a solution in the meantime (thanks to the folks at vbdotnetformums.com, so I would like to share the results:

First possible solution could be defining the parameter as Object and default value as Nothing. Then Cast the DateTime.

Second and cleaner solution (and the one I followed) was to overload the constructor.

Here is the solution by IanRyder (vbdotnetforums.com):

Public Class MyClassExample
  Public Property DateToUseInClass As DateTime

  Public Sub New()
    DateToUseInClass = System.DateTime.Now
  End Sub

  Public Sub New(ByVal GivenDate As System.DateTime)
    DateToUseInClass = GivenDate
  End Sub
End Class

Then I can realise the behavior I wanted to have:

Dim myVariable As New MyClassExample

Dim myVariable As New MyClassExample(DateTime.Today.AddDays(-1))

It worked exactly the way I wanted it. I hope someone else will profit from it some day.

Answer 2

You can set Nothing to default value of function's parameter and then set today's datetime in function

Public Sub New(Optional ByVal fDate As System.DateTime = Nothing)
        If fDate = Nothing Then
            fDate = Now
        End If
    End Sub