Q146120: HOWTO: Use an OLE Control as an Automation Server
Article: Q146120
Product(s): Microsoft C Compiler
Version(s): 4.0,4.1,4.2,5.0,6.0
Operating System(s):
Keyword(s): kbcode kbActiveX kbAutomation kbCOMt kbCtrlCreate kbInprocSvr kbMFC kbVC400 kbVC500 kbV
Last Modified: 12-JUN-2002
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The information in this article applies to:
- The Microsoft Foundation Classes (MFC), used with:
- Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0, 6.0
- Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0, 6.0
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0
- Microsoft Visual C++.NET (2002)
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SUMMARY
=======
In situations where an OLE container doesn't support control containment, you
may want to use an OLE control as an automation server to gain access to its
properties and methods. This article explains the necessary modifications you
need to make in order for an OLE control to function as a normal automation
server.
MORE INFORMATION
================
Prior to Visual C++ 4.0, an OLE Control could be used as an automation server
without any modification. However, in MFC 4.0, the framework's implementation of
IDispatch::Invoke calls the virtual function IsInvokeAllowed to determine if an
automation server is in the appropriate state to handle automation calls. The
default implementation in CCmdTarget::IsInvokeAllowed returns TRUE, implying
that a server can handle automation calls.
In the case of an OLE control, COleControl::IsInvokeAllowed checks to see if the
control has been either initialized or loaded properly through the persistent
storage interfaces. If the control has the appropriate state information, then
this function returns TRUE. When an OLE control is created as a normal
automation server, it is not created as an embedding in the client. Hence, none
of the persistent state initialization will take place, which thereby causes
IsInvokeAllowed to return FALSE. The effect of this is that a call to an
automation object method generates a run-time error of (8000ffff) :
"Catastrophic failure".
In order to use an OLE control only as an automation server, you need to override
COleControl::IsInvokeAllowed() and return TRUE. If any of the control's
properties and methods should not be accessed when invoked as a normal
automation server, then that automation function could be bypassed and/or an
error code can be returned when COleControl::m_bInitialized is FALSE.
Sample Code
-----------
BOOL CMyOleControl::IsInvokeAllowed (DISPID)
{
// You can check to see if COleControl::m_bInitialized is FALSE
// in your automation functions to limit access.
return TRUE;
}
Additional query words: ocx OLE Automation error
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Keywords : kbcode kbActiveX kbAutomation kbCOMt kbCtrlCreate kbInprocSvr kbMFC kbVC400 kbVC500 kbVC600 kbGrpDSMFCATL
Technology : kbAudDeveloper kbMFC kbVCNET
Version : :4.0,4.1,4.2,5.0,6.0
Issue type : kbhowto
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