Article ID: 179692
Article Last Modified on 11/21/2006
APPLIES TO
- Microsoft Foundation Class Library 4.2, when used with:
- Microsoft Visual C++ 4.2 Enterprise Edition
- Microsoft Visual C++ 4.2 Enterprise Edition
- Microsoft Visual C++ 5.0 Enterprise Edition
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 4.2 Professional Edition
- Microsoft Visual C++ 4.2 Professional Edition
- Microsoft Visual C++ 5.0 Professional Edition
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Standard Edition
This article was previously published under Q179692
SUMMARY
When calling methods on a COM server from within OnDraw() or a WM_PAINT message handler of an MFC client application, you may receive an HRESULT of 0x80010005 (RPC_E_CANTCALLOUT_INEXTERNALCALL - it is illegal to call out while inside message filter) as the return value of a COM call to a server.
MORE INFORMATION
MFC has a default implementation of IMessageFilter(COleMessageFilter). IMessageFilter is used by COM servers and clients to selectively handle incoming and outgoing COM messages while waiting for a response from synchronous calls. MFC's implementation allows processing of WM_PAINT messages (to keep the UI updated) on the COM client side, while waiting on a synchronous COM call to a server (for example, a call to an automation method). This is done through IMessageFilter::MessagePending(). Thus, when calling a COM server method inside of a WM_PAINT handler, you could already be in the middle of a call to the server, and therefore receive the error 0x80010005.
As with any Windows application, the code in WM_PAINT handlers should be minimal. If at all possible, do not have any calls to COM servers in WM_PAINT handlers.
To resolve this problem you could use any one of the following three workarounds:
- In the WM_PAINT handler, post yourself a user-defined message; in the handler for the user-defined message, make the call to the COM server.
- Create a secondary UI thread that creates and makes all calls to the COM servers.
Modify MFC's default implementation of MessageFilter::MessagePending(), which currently processes WM_PAINT messages. To do this, derive a class from COleMessageFilter and override the virtual function OnMessagePending():
CMyMessageFilter : public COleMessageFilter { virtual BOOL OnMessagePending(const MSG* pMsg); } BOOL CMyMessageFilter::OnMessagePending(const MSG* pMsg) { //The base class function dispatches WM_PAINT //by returning FALSE no messages are being processed; the //user can add code here to appropriately handle messages. //WARNING: Not processing WM_PAINT messages will cause the user // interface to appear to hang and not update until the // current COM method call returns. return FALSE; }
Then, in the InitInstance() of the CWinApp derived class, unregister the IMessageFilter MFC registers for you when calling AfxOleInit(). Add this code after the call to AfxOleInit(). Then instantiate a class of type CMyMessageFilter and register it:
BOOL CmyApp::InitInstance() { // Initialize OLE libraries and registers default message filter. if (!AfxOleInit()) { AfxMessageBox(IDP_OLE_INIT_FAILED); return FALSE; } CWinThread* pThread = AfxGetThread(); if (pThread != NULL) { // Destroy message filter, thereby unregistering it. delete pThread->m_pMessageFilter; pThread->m_pMessageFilter = NULL; // Create the new message filter object. pThread->m_pMessageFilter = new CMyMessageFilter; ASSERT(AfxOleGetMessageFilter() != NULL); // Register the new message filter object. AfxOleGetMessageFilter()->Register(); } ... ... }
For more information on how message filters work, please see the online documentation on IMessageFilter and COleMessageFilter.
REFERENCES
"Inside OLE", second edition, by Kraig Brockschmidt, Chapter 6, "Local/Remote Transparency," published by Microsoft Press.
Visual C++ Books Online and the MFC source code for the functions mentioned in this article.
(c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Jaganathan Thangavelu, Microsoft Corporation.
Additional query words: 80010005 2147549189 IMessageFilter MessagePending COleMessageFilter OnDraw
Keywords: kberrmsg kbtshoot kbarchitecture kbcontainer kbprb kbcode KB179692