How to Debug Typelib Shadowing

MORE INFORMATION

What Is an Object Library?

An Object Library is a file with an .OLB extension that provides information to OLE Automation controllers (like Visual Basic) about available OLE Automation objects. The Object Browser can be used to examine the contents of an object library to get information about the objects provided.

What is a Type Library?

A Type Library is a file or component within the object library that contains the OLE Automation standard descriptions of exposed objects, properties, and methods.

How to Make Another Application's Objects Available to Your Application

Another application's objects can be made available in your code by setting a reference to that application's object library. This can be done by choosing References from the Tools menu to bring up the References dialog box. Then you can select from a list of references displayed in the Available References box. To view these objects, choose Object Browser from the View menu.

When you refer to an object in code, Visual Basic searches each application selected in the References dialog box in the order the applications are displayed. If two applications use the same name for an object, Visual Basic uses the definition provided by the application listed higher in the Available References box.

What to Do If the Object You Want Lies Further Down in the List

If the object you actually want is defined in an object library futher down in the reference list, you can:

• Use the Priority Buttons of the references dialog box to move the reference that you want higher up in the list. Then deselect and reselect the reference that has now become lower in priority. -or-
  
  
• Determine the correct name of the reference that you want from the Object Brower, and qualify the object type with this complete name. -or-
  
  
• Dimension the referered object as the generic type Object. -or-
  
  
• Get rid of the one of the references if it is not used.

Example

For example, say you have the following code in an add-in:

   Dim ft As Object
   Dim ct As ControlTemplate
   Dim oprop As Property

   ' VBInstance is instance passed to add-in
   Set ft = VBInstance.Application.ActiveProject.ActiveForm

   ' Select first control on the form:
   Set ct = ft.ControlTemplates.Item(0)

   ' Generates Type Mismatch error when oprop is of type Property.
   For Each oprop In ct.Properties
      Debug.print oprop.Name
   Next
				

The Property object is defined both in the DAO and the VBIDE object libraries. If DAO appears ahead of VBIDE in the reference list, a "Type Mismatch" error is generated at the For statement. This occurs because VBIDE's Property object that is actually being used is shadowed by DAO's Property object.

Choose one of the following solutions as a remedy:

• Use the priority buttons of the references dialog box to move the reference to VBIDE higher up than the reference to DAO. Then deselect DAO. Click the dialog's OK button. Bring up the references dialog again. Reselect DAO, and click the OK button again. -or-
  
  
• Declare oprop as: Dim oprop As VBIDE.Property. -or-
  
  
• Declare oprop as: Dim oprop As Object. -or-
  
  
• Get rid of the reference to the DAO object (if it is not being used).