You must call the AfxEnableControlContainer function when you use OLE control containers in Visual C++

Using Visual C++ version 4.0, it is possible to construct OLE Control Containers. These containers must call AfxEnableControlContainer() in their CWinApp::InitInstance(). This call is added automatically if OLE Controls support is checked in AppWizard Step 3, but in some cases, this call must be added manually. This article explains why you need to call AfxEnableControlContainer() and the possible problems that might occur if this call is not made.

AfxEnableControlContainer() is responsible for wiring up the support structure necessary for a CWnd object to contain an OLE Control. This call is added to a project by AppWizard if OLE Controls support is selected. You need to add this call manually in the following cases:

• You are adding control container support to an existing project. -or-
  
  
• The object that will contain the OLE controls is not created directly by AppWizard, such as an OLE Control.

For example, if you are dynamically creating an OLE Control as a child of another OLE Control, the parent control must call AfxEnableControlContainer() in its constructor.

The following list outlines some of the most common problems (others are possible) that can occur if AfxEnableControlContainer() is not called:

• In many cases, you might receive the following TRACE messages in the Output Window of the debugger:

     >>> If this dialog has OLE controls:
     >>> AfxEnableControlContainer has not been called yet.
     >>> You should call it in your app's InitInstance function.
  						

• In other cases, you might encounter the following ASSERT in file Cmdtarg.cpp, line 218:

     ASSERT(afxOccManager != NULL);
  						

• If you place a Masked Edit or some other OLE control on a CFormView and then run the application, you might see a message box indicating:
  Failed to create empty document.