When building an ActiveX control (OLE Control) using Visual C++ prior to version 5.0, you may receive the following error message: With Visual C++ 5.00, no compiler error is generated when building the control. However, both the CAUSE and RESOLUTION sections below still apply.

Back to the top

This error occurs when using the Developer Studio or Class Wizard to add a WM_CLOSE message handler to your ColeControl-derived class. The handler created will have the following format:

   void CEdt_on_ctrlCtrl::OnClose() {
      // TODO: Add your message handler code here and/or call default
      COleControl::OnClose(); // statement generated by VC++ prior to 5.0
      // CWnd::OnClose(); - statement generated by VC++ 5.0
   }
				

However, an ActiveX Control is a COM object and, as such, uses a different mechanism than processing a WM_CLOSE message to close down its window. For this reason, COleControl has overridden OnClose with its own version using the following prototype:

   void OnClose(DWORD dwSaveOption);
				

COleControl::OnClose has one parameter that is the reason for the error message.

Back to the top

Because the ActiveX Control doesn't handle the WM_CLOSE message, if you want to do some processing when the OLE control is terminating, you can override the COleControl::OnClose function as follows:

Add the following function prototype to the class definition in the header file for your COleControl derived class (in this example, CEdt_on_ctrlCtr):

   void OnClose(DWORD dwSaveOption);
				

To replace CEdt_on_ctrlCtrl with the name of your OLE control class, add the following implementation in the .cpp file:

   void CEdt_on_ctrlCtrl::OnClose(DWORD dwSaveOption) {
      // TODO: Add your message handler code here and/or call default
      COleControl::OnClose(dwSaveOption);
   }
				

Back to the top

This behavior is by design.

Back to the top