As a former VB6 programmer, I am used to being able to test for a null reference

e.g.: 
If ObjectReference = null then 
     'Do Stuff
End If

I know that .net does not support direct testing for null (or,
"nothing" in this case). I would like to know the best way to test an
object reference for a null value.

I am using an array of a custom class to hold school grade entries
deleted from a listbox, so that a user may undo the deletion of an
entry (up to the 20 most recent deletions). My "btnRestore" click
event has code similar to the following:

'module level declarations
Dim intDeletedGradeIndex as Integer
Dim DeletedGrades(20) as GradeEntry

   Private Sub btnRestore_Click(ByVal sender As System.Object, _
   ByVal e As System.EventArgs) Handles btnRestore.Click

            ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
            'If DeletedGrades(intDeletedGradeIndex) <> Nothing Then'
            ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
            DeletedGrades(intDeletedGradeIndex).ListBoxDisplay(lstGrade)
            DeletedGrades(intDeletedGradeIndex) = Nothing
            intDeletedGradeIndex -= 1
            ''''''''
            'End If'
            ''''''''
    End Sub

Thanks,
Sceleratus

---

Clarification of Question by sceleratus-ga on 25 Apr 2004 17:41 PDT

Thanks for clearing that up. I was confused. You are correct in
assuming I was refering to ADO.NET. I must not have been forming my
boolean expressions correctly in vb.

Sceleratus-

.Net most definatly supports Null reference types (and checking for Null)

Quick example

VB:

        Dim obj As Object = Nothing

        If Not obj = Nothing Then
            MessageBox.Show("Is Not Nothing")
        Else
            MessageBox.Show("Is Nothing")
        End If

C#:

       object obj = null;

       if(obj != null)
       {
           MessageBox.Show("Is Not Nothing")
       }
       else
       {
           MessageBox.Show("Is Nothing")
       }

When you say ".Net does not support direct testing for null", I think
you may be refering to ADO.NET.

If your have a field in a ADO.NET table that is null you have to compare its
value against System.DBNull.Value, you cannot do a direct test against
null (or nothing).  However this does not affect you here.

Regards,

Brett