{String1 = Nothing or "Blahblah"} ... String1 should = "Blahblah" not exception?

[JBlue]

{String1 = Nothing or "Blahblah"} ... String1 should = "Blahblah" not exception?

Hi everyone, I'm brand new here, sorry about the title but it was the best way I could summarise my problem.

My code scenario is this:

Dim String1 as String
Dim PotentialNullString as String = Nothing



String1 = PotentialNullString Or "This is an Empty String"

Now this code returns a null reference exception. What I want is a way to get String1 to get the value of PotentialNullString but if that happens to be Nothing then it should be "This is an Empty String".

I know this is quite easily doable by checking If PotentialNullString IsNot Nothing first but I want to do it all on one line, one expression.

Is this possible?

 

[JohnH]

If Operator (Visual Basic) see "If Operator Called with Two Arguments"

        Dim PotentialNullString As String = Nothing

        Dim String1 = If(PotentialNullString, "This is an Empty String")

 

[JBlue]

Ah thanks for the reply JohnH. I had tried the If operator with two arguments and it didn't work and on double checking I noticed it works in this scenario but my actual scenario was a little more complicated. It involved a Null object reference as opposed to just an empty string. This problem happens when the string is from another object. I'll try explain this better this time:

Public Class Book
Public Title as String
End Class

Public Sub TheProblem()

Dim String1 as String
Dim NullBook as Book = Nothing

String1 = If(Book.Title, "Invalid Book") 'This line causes a nullreference exception
End Sub

Because Book doesn't exist its faulting on getting the title value, but in principal shouldn't it work in the same manner as you suggested to me?

 

[JohnH]

You mean NullBook.Title, not Book.Title. No, there would have to be a Book object for that to work, accessing the Title property on a null reference throws that exception.
You have to use the If operator with three arguments, checking for object before using it:

Dim String1 = If(NullBook IsNot Nothing, NullBook.Title, "Invalid Book")

This would still not have the exact same meaning, because the Title can be Nothing also.

 

[JBlue]

You have to use the If operator with three arguments, checking for object before using it

Perfect, this is exactly what I was looking for. I didn't realise I could use more than 2 arguments for If().

Thanks for your help!

 

[JohnH]

Perfect, this is exactly what I was looking for. I didn't realise I could use more than 2 arguments for If().!

So you didn't read the article I linked to? It was for you I posted it.