Unable to call trivial OCX from VB

George V. Reilly -- georger@microcrafts.com
Tuesday, October 15, 1996

Environment: NT 4.0, VC 4.1, VB 4.0

I'm trying to create an ActiveX control that I can
call from VBscript.  I couldn't get it working there,
so I'm trying to do it in VB 4.0.

I created an OCX with the OLE ControlWizard
and added a couple of trivial methods.  When I try
to call any of them from VB---even the Wizard-provided
one of AboutBox---I get a runtime error of 8000FFFF
(E_UNEXPECTED), a "catastrophic failure" of OLE
automation.

I'm using the following procedure which is
attached to an input box.  When Enter is pressed,
the object gets created and then one of its methods
is called.

Private Sub Input_KeyPress(KeyAscii As Integer)
    If (KeyAscii = 13) Then
        Dim Hello As Object

        Set Hello = CreateObject("HELLOWORLD.HelloWorldCtrl.1")
    
        ' Hello.TestEcho("Foo")
        Hello.AboutBox

        Set Hello = Nothing
    End If
End Sub

I've saved the VB program as an EXE and tried
running it in VC 4.1.  The object gets constructed
successfully, but it fails in COleDispatchImpl::Invoke.
It calls IsInvokeAllowed, which returns FALSE
(m_bInitialized has not been set).

A friend of mine thought that it might be something
to do with the ODL file generated by the Wizard,
but when put on the spot, was unable to pinpoint
the problem or produce a reference.

All of this confirms my longstanding prejudice that
OLE and VB are evil, but that's not getting me anywhere.

TIA.
-- 
/George V. Reilly      
MicroCrafts, Inc., 17371 NE 67th Ct #205, Redmond, WA 98052, USA.
Tel: +1 206/250-0014  Fax: 206/250-0100  Web: www.microcrafts.com
Vim 4 (vi clone) for NT & Windows 95: http://www.halcyon.com/gvr/
pgp fingerprint: e2 b4 83 64 11 52 21 ea  bf d8 51 c2 11 00 78 fc

---

Neil Hodgson -- ip104@astsun.fujitsu.com.au
Thursday, October 17, 1996

[Mini-digest: 2 responses]

   George V. Reilly wrote on October 16, saying "Unable to call trivial OCX
from VB"

   This is a limitation in MFC's OCX implementation. To access the OLE
Automation interface of an MFC OCX, that OCX must be fully intantiated and
loaded. Often, it makes no sense to call the OA interface before the OCX's
properties have been loaded. The CreateObject in your example is simply
doing a CoCreateInstance which will not perform all the needed operations.
You could modify your OCX to make it accept incoming automation calls
without full instantiation but I think the solution to your problem is much
simpler. 

   To do what you want, you should place the OCX on a Visual Basic form.
Then you may call  its automation interface. This way it is fully loaded
and happy to accept calls before you call it. Similarly in VBScript, place
the OCX on the page.

					Neil Hodgson
-----From: "George V. Reilly" 

To answer my own question:
> I created an OCX with the OLE ControlWizard
> and added a couple of trivial methods.  When I try
> to call any of them from VB---even the Wizard-provided
> one of AboutBox---I get a runtime error of 8000FFFF
> (E_UNEXPECTED), a "catastrophic failure" of OLE
> automation.

It is necessary to override COleControl::IsInvokeAllowed
to return TRUE.  KnowledgeBase article Q146120:
"How to Use an OLE Control as an Automation Server"
sort of explains why.
-- 
/George V. Reilly      
MicroCrafts, Inc., 17371 NE 67th Ct #205, Redmond, WA 98052, USA.
Tel: +1 206/250-0014  Fax: 206/250-0100  Web: www.microcrafts.com
Vim 4 (vi clone) for NT & Windows 95: http://www.halcyon.com/gvr/
pgp fingerprint: e2 b4 83 64 11 52 21 ea  bf d8 51 c2 11 00 78 fc

---

Dublin-ISG2@stercomm.com
Friday, October 18, 1996

[Mini-digest: 2 responses]

   George V. Reilly wrote on October 16, saying "Unable to call trivial OCX
from VB"

   This is a limitation in MFC's OCX implementation. To access the OLE
Automation interface of an MFC OCX, that OCX must be fully intantiated and
loaded. Often, it makes no sense to call the OA interface before the OCX's
properties have been loaded. The CreateObject in your example is simply
doing a CoCreateInstance which will not perform all the needed operations.
You could modify your OCX to make it accept incoming automation calls
without full instantiation but I think the solution to your problem is much
simpler. 

   To do what you want, you should place the OCX on a Visual Basic form.
Then you may call  its automation interface. This way it is fully loaded
and happy to accept calls before you call it. Similarly in VBScript, place
the OCX on the page.

                                        Neil Hodgson
-----From: "George V. Reilly" 

To answer my own question:
> I created an OCX with the OLE ControlWizard
> and added a couple of trivial methods.  When I try
> to call any of them from VB---even the Wizard-provided
> one of AboutBox---I get a runtime error of 8000FFFF
> (E_UNEXPECTED), a "catastrophic failure" of OLE
> automation.

It is necessary to override COleControl::IsInvokeAllowed
to return TRUE.  KnowledgeBase article Q146120:
"How to Use an OLE Control as an Automation Server"
sort of explains why.
-- 
/George V. Reilly      
MicroCrafts, Inc., 17371 NE 67th Ct #205, Redmond, WA 98052, USA.
Tel: +1 206/250-0014  Fax: 206/250-0100  Web: www.microcrafts.com
Vim 4 (vi clone) for NT & Windows 95: http://www.halcyon.com/gvr/
pgp fingerprint: e2 b4 83 64 11 52 21 ea  bf d8 51 c2 11 00 78 fc

---

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