FIX: Assertion Failed Line 388 of Occmgr.cpp

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++, 32-bit Edition, version 4.0

SYMPTOMS

When an MFC 4.0 control container has one or more invisible-at-run-time OLE controls along with other OLE and non-OLE controls placed on a dialog template, the following assertion might occur based on the tab-order of the controls in the dialog:

   Debug Assertion Failed!
   Program: <app name>
   File: occmgr.cpp
   Line: 388

CAUSE

When the MFC framework creates an invisible-at-run-time OLE control, it is reparented to the desktop window. This makes the control's window not a sibling of the other windows present in the dialog. Now if this invisible- at-run-time control has another OLE control (visible at run time) next in tab order, then the framework places the latter OLE control at the end of the dialog's child window list. Later when the framework attempts to find the "next" sibling window of the OLE control (now at the end of the dialog's child window list), it returns NULL because there is no "next" sibling window to this OLE control.

RESOLUTION

The assertion can be safely ignored, but the tab order will probably be incorrect. To work around this assertion, place the invisible-at-run-time controls at the end of the tab order in the dialog template.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug was corrected in Visual C++ 4.1.

MORE INFORMATION

The MFC framework creates OLE controls placed on a dialog template resource, if any, by calling COccManager::CreateDlgControls. This function in turn makes a call to COccManager::CreateDlgControl to create a specific OLE control. The code present in CreateDlgControl attempts to setup the tab order of each OLE control after it is created, for which it calls CWnd::SetWindowPos, passing in the handle of the window that the control will be inserted after (in the code, this window is referred to as pWndAfter).

For a clear understanding of what would generate the above described ASSERT, consider the following reproducible scenario.

Steps to Reproduce the Assertion Failure

Create a dialog-based control container application, and place the following controls with the specified tab order in its main dialog template resource:

• MS-COMM OLE Control (or any invisible-at-run-time control) : 1
• GRID OLE control (or any control that is visible at run time) : 2
• Static control (or any standard Windows control) : 3
• GRID OLE control (or any control that is visible at run time) : 4