问题:

Possible Duplicates:
Coalesce operator and Conditional operator in VB.NET
Is there a VB.NET equivalent for C#'s ?? operator?

Is there a built-in VB.NET equivalent to the C# null coalescing operator?

回答1:

Yes, there is, a long as you're using VB 9 or later (included with Visual Studio 2008).

You can use the version of the If operator overloaded to accept only two arguments:

Dim myVar? As Integer = Nothing
Console.WriteLine(If(myVar, 7))

More information can be found here in a blog post by the VB.NET team.

(Yes, this is an operator, even though it looks like a function. It will compile down to the same IL as the "proper" null-coalescing operator in C#.)

Example

Dim b As Boolean?
Console.WriteLine("{0}.", If(b, "this is expected when b is nothing"))
'output: this is expected when b is nothing.

b = False
Console.WriteLine("{0}.", If(b, "this is unexpected when b is false"))
'output: False.

b = True
Console.WriteLine("{0}.", If(b, "this is unexpected when b is true"))
'output: True.