Is there such a thing as a nullable bool in vb.net

Question

I am working through my new MVC book and of course, the samples are all in c# as usual.

There is a line of code that says

public bool? WillAttend { get; set; }

The author explains that the question mark indicates that this is a nullable (tri-state) bool that can be true, false. or null. (A new C# 3 convention.)

Does vb.net support any convention like this. Certainly I can declare a boolean in vb.net and I can explicitly set it to Null (Nothing in vb.net).

What's the difference. IS there more to it in c#. Advantages?

Answer 1

You can declare a nullable value 3 ways in VB:

Dim ridesBusToWork1? As Boolean
Dim ridesBusToWork2 As Boolean?
Dim ridesBusToWork3 As Nullable(Of Boolean)

Further Reading: MSDN - Nullable Value Types (Visual Basic).

Answer 2

1. bool? is just shorthand syntax for a nullable value type: i.e. Nullable<bool>
2. In VB.NET you can use either one: Boolean? or Nullable(Of Boolean).

You can write it like this with a backing property:

Private _willAttend As Nullable(Of Boolean)
Public Property WillAttend As Nullable(Of Boolean)
    Get
        Return _willAttend
    End Get
    Set(value As Nullable(Of Boolean))
        _willAttend = value
    End Set
End Property

Or just use an auto-implemented property like this:

Public Property WillAttend As Boolean?

Answer 3

Nullables are available since .NET 2.0. In that version Microsoft implemented Generics (Nullable is a Generic type). Since .NET 3.0 you are able to use the ? in VB.NET too (previously you were only able to use Nullable(of Boolean)).

So as said by Lucas Aardvark in .NET 3.0 you are able to use 3 declarations of nullables, but in .NET 2.0 only 1 being

Dim myBool as Nullable(of Boolean)