Nullable Types in VB.NET?

Question

VB.Net does have nullable types, they can be declared in the following two different ways.

Dim iNullable As Integer?

or

Dim iNullable As Nullable(Of Integer)

Nullable types can be used in VB.NET same as in C#.

You can't assign Null, Nothing or DBNull to a bare Integer in VB but you can use a Nullable(Of Integer) instead:

Dim x As Integer? = Nothing

Alternatively, it sometimes (but rarely) makes sense to box the integer value in an Object (which can be Nothing).

Integers (System.Int32 etc) in .NET are not directly nullable; however, there is Nullable-of-T that allows you to make any value-type nullable-ish. Note that you may have to check the database against DBNull rather than null/Nothing.

So yes, you can do something very similar.

In a number of cases Nothing will get converted to the default value. To use Nothing the same way you would use null you need to cast it to the correct nullable type.

Dim str As String
Dim int As Nullable(Of Integer) ' or use As Integer?
Dim reader As SqlDataReader
Dim colA As Integer = reader.GetOrdinal("colA")
Dim colB As Integer = reader.GetOrdinal("colB")
str = If(reader.IsDBNull(colA), DirectCast(Nothing, String), reader.GetString(colA))
int = If(reader.IsDBNull(colB), DirectCast(Nothing, Nullable(Of Integer)), reader.GetInt32(colB))