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.
回答2:
According to this question it would seem the answer is If()
回答3:
No. Use GetValueOrDefault; that's why it's there!
回答4:
I don't believe that there is a built in VB.Net equivalent, but here's an answer: null coalesce operator in VB.Net(8)
来源：https://stackoverflow.com/questions/6792729/vb-net-null-coalescing-operator