VB Forum / COM / June 2008

Has anyone seen an instance where On Error Resume Next was NOT successful in
suppressing a run-time error?

I have an application which uses Automation to control Word and Excel. It's
tricky because we need to support Office 2000, XP, 2003 and 2007. Obviously,
within our code one of the first things we do is determine the version so
that we know which functions are or are not available. However, beyond that,
compilation is tricky as well since we need to ensure that in the IDE we
reference the Word9 and Excel9 object libraries, in order to pick up the
lowest common denominator interface at compile time, which will support any
version of the corresponding interfaces found on the box at run-time.

Anyway, one of our build boxes got messed up and our application was
compiled against the Office 2003 interfaces. We picked up the problem during
testing on an XP environment since the application threw an untrapped error
up to the calling method: Automation error;The object invoked has
disconnected from its clients. We spent quite a while tracking down the
problem, finally resolved it to the incorrectly configured build platform,
fixed it, recompiled and the application works fine.

Which is why I can't justify spending a whole lot of additional effort on
this, but we picked up something very strange during our debugging, which I
have not seen in over a decade of VB6 development.

   On Error Resume Next ' First try the more sophisticated open syntax
   PostEvent C_LIB, C_CLASS, "zViewWordDoc", srsEvtInfo, "Before
m_AppWord.Documents.Open(" & m_Document & ")"
   Set m_DocWord = m_AppWord.Documents.Open(CStr(m_Document), False, True,
False)
   PostEvent C_LIB, C_CLASS, "zViewWordDoc", srsEvtInfo, "Just After
m_AppWord.Documents.Open(" & m_Document & ")"

We know the error occured on the Set statment, since we received the first
PostEvent message, but not the second. What we can't figure out is, with a
covering On Error Resume Next in effect, how an automation error would cause
an untrapped error to be thrown up to the calling method. The whole purpose
of the On Error Resume Next in this context is to first attempt an Open
operation which is supported by Office 2000 and higher. If that operation
fails then we attempt a different Open operation which is backward
compatible with XP/2000. And this error suppression works well. But for some
reason, the Automation error;The object invoked has disconnected from its
clients, does not get suppressed by the On Error Resume Next. Is there an
explanation for this behavior?

Thanks for your advice!

Joseph Geretz