HOWTO: How to Access a Subclassed Windows Control in an OLE Control (135048)

SUMMARY

The ControlWizard provided with the CDK allows a new OLE control to be created by subclassing a common Windows control such as a button, toolbar, or edit box. The XLIST sample provided with the CDK illustrates how to do this by subclassing a Windows list box. The XLIST sample communicates with and manipulates the subclassed Windows control by using the Windows SendMessage() API. For example, to insert a string into the subclassed list box, use this code:

   SendMessage(LB_INSERTSTRING, nIndex, (long)lpstrText);

Because MFC provides wrapper classes for the common Windows controls, it would be useful to be able to use these classes to communicate with the subclassed control. This article illustrates one technique for doing this by showing how to connect the appropriate MFC control class to the COleControl-derived class that subclasses a Windows control.

MORE INFORMATION

The following sample code illustrates how to use the MFC CListBox class to communicate with a Windows list box control subclassed by an OLE control. The process for doing this is as follows:

Add a member variable of type CListBox to the declaration of the COleControl derived class:

   class CSubclassCtrl : public COleControl
   {
   ...
   // Implementation
   protected:

     CListBox  m_ListBox;
   ...
   }

Override the OnCreate member of the COleControl derived class and initialize the m_hWnd member of the CListBox member:

   int CSubclassCtrl::OnCreate(LPCREATESTRUCT lpCreateStruct)
   {
   if (COleControl::OnCreate(lpCreateStruct) == -1)
   return -1;

   m_ListBox.m_hWnd = m_hWnd;

     // Additional list box initialization can go here.

   return 0;
   }

Set the m_hWnd member of the CListBox member to NULL in the destructor of the COleControl derived class:
```
   CSubclassCtrl::~CSubclassCtrl()
   {
     m_ListBox.m_hWnd = NULL;
   }
						
```

After completing these steps, the m_ListBox member can be used to manipulate the subclassed Windows list box. For example, instead of using the Windows SendMessage() API to insert a string into the list box, the following CListBox method can be called:

   m_ListBox.InsertString(nIndex, _T("A String"));