I have a global variable that is an instance of my custom class.
How do I check if the object is set or if I need to initialize it?
Add a comment
|
3 Answers
If obj Is Nothing Then
' need to initialize obj: '
Set obj = ...
Else
' obj already set / initialized. '
End If
Or, if you prefer it the other way around:
If Not obj Is Nothing Then
' obj already set / initialized. '
Else
' need to initialize obj: '
Set obj = ...
End If
answered Apr 13, 2010 at 17:22
stakx - no longer contributing
85.1k20 gold badges176 silver badges277 bronze badges
5 Comments
Icode4food
I knew it had to be simple when I Googled it and found nothing! Thanks for your help!
Matt Browne
Note that checking
obj Is Nothing is NOT the same as checking IsNothing(obj)! Thanks for the correct syntax to check this...not sure why IsNothing() behaves differently...
Martin F
I find
Not (obj Is Nothing) easier to understand than Not obj Is Nothing. My brain doesn't know what a "Not obj" is!
Alexandre
You can also write : If obj IsNot Nothing which I find it much more clearer than the rest. It also kinda feel the same as C# (ojb != null)
Hristo
Thanks for the short and clear answer! IMO, the straight read "if obj is nothing then create the obj else exit" is the best human readable syntax. The double negation is weird, even in real human relations...
When using global variables it's possible to run into a situation in which the object is empty. So, the code:
If Not obj Is Nothing Then
'obj is already set
Else
'set obj
End If
produces an 'object required' error.
In this situation, the following works:
'First check it is initialized
If IsObject(obj) Then
'Then check if it is set
If Not obj Is Nothing Then
'obj is set
Else
'set obj
End If
Else
'set obj
End If
The (un)safe way to do this - if you are ok with not using option explicit - is...
Not TypeName(myObj) = "Empty"
This also handles the case if the object has not been declared. This is useful if you want to just comment out a declaration to switch off some behaviour...
Dim myObj as Object
Not TypeName(myObj) = "Empty" '/ true, the object exists - TypeName is Object
'Dim myObj as Object
Not TypeName(myObj) = "Empty" '/ false, the object has not been declared
This works because VBA will auto-instantiate an undeclared variable as an Empty Variant type. It eliminates the need for an auxiliary Boolean to manage the behaviour.
3 Comments
Andre
Nobody should ever have any VBA code without
Option Explicit. It gains nothing except problems. To "switch" behavior, use Conditional Compiling.
Cool Blue
@andre, yes, fair point. I feel ok without it because I use hungarian notation for scope, but I try to avoid vba these days if I can. Most of what I see is about explicit declarations, name safety and avoiding the dreaded variants. What are your key reasons?
Patrick Lepelletier
In fact i get "Nothing" as result of typename , and not "Empty"