SAMPLE: Subclassing VBX Controls with MFC 2.0

• Microsoft Windows Software Development Kit (SDK) for Windows version 3.1

SUMMARY

SUBVBX is a sample application that does Windows subclassing on a VBX control using the Microsoft Foundation Class (MFC) Libraries version 2.0. The sample subclasses the grid control, overrides the OnDlgCode() message handler, and returns the DLGS_WANTARROWS code. Normally Windows uses the arrow keys to move between controls in a dialog box, and does not pass the arrow keys to the control. Subclassing the grid control and overriding the OnDlgCode() message handler causes Windows to pass the arrow keys to the grid control so that it can use the keys to move between cells in the control.

Download SUBVBX.EXE, a self-extracting file, from the Microsoft Software Library (MSL) on the following services:

• Microsoft Download Service (MSDL)

        Dial (206) 936-6735 to connect to MSDL
        Download SUBVBX.EXE (size: 90235 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the \SOFTLIB\MSLFILES directory
        Get SUBVBX.EXE (size: 90235 bytes) 
  

MORE INFORMATION

Windows controls, such as an edit control or a list box control, can be subclassed in MFC using the CWnd::SubclassWindow() and CWnd::SubclassDlgItem() functions. These functions do not work for VBX controls. These functions rely on the fact that each window control has its own Windows procedure. This way it is possible for an MFC object to chain to the control's original Windows procedure. However, Visual Basic (VB) controls under MFC 2.0 are managed by MFC objects, and therefore VB controls use the same Windows procedure as all other MFC objects.

To subclass a VB control in MFC 2.0, it is necessary to copy the data from the original control object into the object that you want to use to subclass the original control. After the original object has been copied, it can be detached and deleted, and the new control object can be attached.

This sample defines the CVBClone class that contains the function SubclassVBControl(). This function does the copying, attaching, and detaching that is described above. To use this class, derive a new class from the CVBClone class and new message handling functions to the message map. This class can then be used to subclass a VB control in a dialog box by calling the SubclassVBControl() function in the OnInitDialog() or OnInitialUpdate() function of the dialog box or form view that contains the control.

This sample subclasses a grid control in a form view. The sample defines the CMyGrid class from CVBControl, which it uses to subclass the control. The sample also calls SubclassVBControl in the OnInitialUpdate() of the form view to subclass the control in the form view.