INFO: COM Method Call in WM_PAINT Handler Returns 0x80010005

ID: Q179692

The information in this article applies to:

The Microsoft Foundation Classes (MFC), included with:
- Microsoft Visual C++, 32-bit Editions, versions 4.2, 4.2b, 5.0, 6.0

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. -or-

Create a secondary UI thread that creates and makes all calls to the COM servers.

-or-

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 COleMessageFiler
      {
         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 kbvc420 kbvc500 kbvc600

Keywords : kbcode kbole kbMFC kbVC
Version : WINNT:4.2,4.2b,5.0,6.0
Platform : winnt
Issue type : kbinfo