Bob / Jim,

Thanks for the ideas.

In my particular situation, I don't mind if the add-in does not exist -- I
will simply disable any features that reference the add-in.

However, the problem is that if VBA attempts to compile any code that
references the add-in BEFORE running the code that checks if the add-in
exists, the application will still halt with a compile error.

EXAMPLE 1:
In this example, only the local class clsLocalClass makes any reference to
the add-in. However if the add-in does not exist the Workbook_Open event
will never run because VBA will first attempt to compile BOTH the
ThisWorkbook and clsLocalClass. If the add-in is not loaded then the
clsLocalClass compile will fail, and Workbook_Open will never run.

In ThisWorkbook class:
================================================== ==========

Dim objLocal As clsLocalClass

Sub Workbook_Open()
Dim sResult

On Error Resume Next
sResult = Application.AddIns("MyAddIn").Installed
If sResult Then
'' Add-in exists -- make use of it
Set objLocal = New clsLocalClass
Else
'' Add-in does not exist -- don't use features from Addin
End If
End Sub

------------------------------------------------------------
In clsLocalClass (inside current project)
------------------------------------------------------------
Dim objAddin As AddIn.clsSomething

Private Sub Class_Initialize()
Set objAddin = CreateSomething()
End Sub

================================================== ==========

EXAMPLE 2:
The code below WILL ACTUALLY WORK, but it seems risky. I made two changes:
changed the objLocal definition to Object instead on clsLocalClass, and I
moved the New clsLocalClass line out of Workbook_Open. In this particular
scenario, VBA will not attempt to compile clsLocalClass, so the
Workbook_Open event will run.

It SEEMS RISKY trying to second-guess when/if VBA will decide to compile
clsLocalClass. My real-world scenario is obviously more complex, and if VBA
were to attempt to compile clsLocalClass at any time for any reason, my
application would halt.

In ThisWorkbook:
================================================== ==========
Dim objLocal As clsLocalClass

Sub Workbook_Open()
Dim sResult

On Error Resume Next
sResult = Application.AddIns("MyAddIn").Installed
If sResult Then
'' Add-in exists -- make use of it
IntializeApp
Else
'' Add-in does not exist -- don't use features from Addin
End If
End Sub

Private Sub IntializeApp()
Set objLocal = New clsLocalClass
End Sub

------------------------------------------------------------
In clsLocalClass (inside current project)
------------------------------------------------------------
Dim objAddin As AddIn.clsSomething

Private Sub Class_Initialize()
Set objAddin = CreateSomething()
End Sub

================================================== ==========



"Jim Rech" wrote in message
...
How about:

ThisWorkbook.VBProject.References.AddFromFile "c:\book1.xla"

--
Jim Rech
Excel MVP
"Lee S" wrote in message
...
| In my spreadsheet I have code that references functions and classes in
an
| .XLA file. When a user who does not have the .XLA file available opens
the
| spreadsheet they see a compile error when the Workbook Open event fires
| (even though the Open event itself does not call or even directly
reference
| any XLA resources).
|
| This actually makes perfect sense to me ... but that does not mean I
have
| to like it.
|
| Anyone know of a reliable way to prevent the compile error in this
| situation?
|
| Something comparable to late binding for functions in an XLA library
would
| be nice. Then I could check if the library exists before I decide
whether
| to make the function calls.
|
| I have discovered that if arrange my code /just right/, I can avoid the
| error by convincing VBA not to compile the modules that reference the
| non-existent library -- however that is not reliable enough to release
to
| the users.
|
| I am tempted to port my .XLA into a Visual Basic and compile it into an
| ActiveX DLL, but I figured I would check with the group to see if anyone
had
| a good idea on this.
|
| Thanks!
| Lee
|
|