BUG: Enumerated Type Parameters Break Binary Compatibility (184286)


The information in this article applies to:

  • Microsoft Visual Basic Control Creation Edition for Windows 5.0
  • Microsoft Visual Basic Learning Edition for Windows 5.0
  • Microsoft Visual Basic Professional Edition for Windows 5.0
  • Microsoft Visual Basic Enterprise Edition for Windows 5.0
This article was previously published under Q184286

SYMPTOMS

When developing an ActiveX DLL or ActiveX EXE, Visual Basic might erroneously report that you have broken Binary Compatibility when you try to compile your project. This could happen even if you have not changed a single line of code in your project.

CAUSE

The most common cause for this problem is a known bug, in which ENUMS is used as a function parameter.

For example, if you have the following line of code in an ActiveX DLL: 
   Public Property Get MyProp(NewValue As MyEnum) as clsMyClass
When you try to compile this code with Binary Compatibility turned on, you might receive the following error:
MyProp in the MyClass Class Module has arguments and a return type that is incompatible with a similar declaration in version component.
When you receive the error, you can click the "Show Declaration" command button (which shows you the version-compatible declaration of the function and the declaraton in the current project). Note that the two declarations are exactly the same, even though Visual Basic gives the error.

Service Pack 3 for Microsoft Visual Studio addresses this issue, but does not always fix the bug.

For additional information, please see the following article in the Microsoft Knowledge Base:

171819 FIX: Invalid Enum Value Causes Incompatible Binary Compatible

RESOLUTION

The following are three suggested workarounds for this bug:
  • Do not use Binary Compatibility. This is NOT a good workaround because any client using the ActiveX component must be recompiled each time modifications are made to the component.
  • Rename all Enum statements as Long. For example, change the following code from: 
    Public Property Get MyProp(NewValue As MyEnum) As clsMyClass
    -to- 
    Public Property Get MyProp(NewValue As Long) as clsMyClass
    This workaround eliminates the Binary Compatibility bug problem; however, there is an associated problem. You lose the "Intellisense" feature when you are programming the ActiveX component.
  • Place all ENUMS into a separate DLL, and reference the DLL to get the Type Library information about the ENUMS. This workaround ensures that compatibility is kept, and maintains the "Intellisense" feature. This workaround is described in more detail below.

Steps to Implement the Type Library Workaround

The Binary Compatibility bug usually occurs with very large projects, and late in development. However, if you do start receiving broken Binary Compatibility error messages, you should do the following:
  1. Copy all ENUM declarations into a new ActiveX DLL.
  2. Go to the select Project Properties from the Project menu and select the Component tab.
  3. Select the Remote Server Files option. This will make sure that a TLB file is generated when the ActiveX DLL is compiled. A TLB file contains the Type Library for the ActiveX Component it is associated with.
  4. Save the ActiveX DLL for future use.
  5. Compile the ActiveX DLL
  6. Unregister the ActiveX DLL you just compiled by doing the following, select Run from the Windows Start menu and type in the following command:

    <Path to RegSvr32>\Regsvr32.Exe /u <Path to Project>\ProjectName.DLL
  7. Load up the actual ActiveX Server that is raising the broken Binary Compatibility error message.
  8. Make sure all the ENUM declarations have been removed.
  9. Select References from the Project menu.
  10. From References, select the "Browse" button.
  11. Locate and select your newly created TLB file.
  12. Compile your ActiveX server. The error message will no longer appear.
You can also bypass unregistering the ActiveX DLL which contains the ENUM declares, and reference the DLL itself instead of the TLB file.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.
Modification Type:MinorLast Reviewed:3/11/2005
Keywords:kbBug kbpending KB184286
©2004 Microsoft Corporation. All rights reserved.