PRB: Problems with CMDIFrameWnd Toolbar Combo Box

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with:

      - Microsoft Visual C++ for Windows, versions 1.0 and 1.5
  

SYMPTOMS

Using AppWizard, create an MDI application that contains a toolbar. Add a combo-box control to the toolbar using the same method that the CTRLBARS sample uses (see CMainFrame::CreateStyleBar() to create a combo box on the toolbar).

When you drop the list-box portion of the combo box down and move the parent-frame window, the list box detaches from the edit-box portion of the combo box. With the CTRLBARS sample, the list box closes as soon as you click the frame window.

CAUSE

This behavior is ultimately caused by a problem in the combo-box control in Windows. For additional information, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q76365
   TITLE     : PRB: Moving or Resizing the Parent of an Open Combo Box

RESOLUTION

To work around this problem, you should handle WM_PAINT messages in your MDI application for the parent-frame window of the combo box and send the combo box a message directly. For example, if your frame window is class CMainFrame, if your toolbar is called MyToolBar, and if MyToolBar has a combo box named MyCombo, your OnPaint() would look like this:

   CMainFrame::OnPaint()
   {
   ...
      MyToolBar.MyCombo.SendMessage(CB_SHOWDROPDOWN, FALSE);
   ...
   }