Q168326: HOWTO: Define the Display Size of an MFC ActiveX Control

Article: Q168326
Product(s): Microsoft C Compiler
Version(s): 4.2,4.2b,5.0,6.0
Operating System(s): 
Keyword(s): kbole kbActiveX kbCOMt kbCtrl kbMFC kbVC420 kbVC500 kbVC600 kbDSupport kbGrpDSMFCATL
Last Modified: 10-JUN-2002

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 4.2b, 5.0, 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 4.2b, 5.0, 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
   - Microsoft Visual C++.NET (2002) 
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NOTE: Microsoft Visual C++ .NET (2002) supports both the managed code model that is provided by the .NET Framework and the unmanaged native Windows code model. Part or all of the information in this article applies to managed Visual C++ code and may be applied only by using the .NET Framework.

SUMMARY
=======

Sometimes you need to limit an ActiveX control's minimum or maximum size at
design time. This article explains how to do this by overriding the virtual
COleControl::OnSetExtent method.

MORE INFORMATION
================

The COleControl::OnSetExtent method is called by
COleControl::XOleObject::SetExtent. COleControl::XOleObject is COleControl's
IOleObject implementation. A container calls IOleObject::SetExtent when it needs
to dictate to an embedded object the size at which it will be displayed.

COleControl::OnSetExtent takes one parameter, a pointer to a SizeL structure. The
SizeL structure contains the new size that the container is requesting for the
control in HIMETRIC units.

If a you need to limit a control to a certain size, you need to make it override
COleControl::OnSetExtent and do the following:

1. Make any necessary unit conversions on the SizeL structure passed in.

2. Check the size in the SizeL structure that was passed in.

3. If the control cannot accommodate the request, return false.

4. Otherwise, pass the (unmodified) SizeL to the base class' implementation of
  OnSetExtent.

See the Sample Code section below for an example of how to override
COleControl::OnSetExtent to limit the size of an ActiveX control.

Sample Code
-----------

The following code snippet shows how to override COleControl::OnSetExtent so that
the height of the control will never be smaller than 20 pixels.

      BOOL CTestCtrl::OnSetExtent(LPSIZEL lpSizeL)
        {
           // This function limits the height of a control to be at
           // least 20 pixels.

           // Use the desktop window to get a DC so we can use
           // CDC::HIMETRICtoDP and CDC::DPtoHIMETRIC
           CWnd *pWnd = CWnd::FromHandle(::GetDesktopWindow());
           CClientDC dc(pWnd);

           CSize sz(lpSizeL->cx,lpSizeL->cy);
           dc.HIMETRICtoDP(&sz); //Convert the size to pixels

           if (sz.cy < 20)
              return false;

           return COleControl::OnSetExtent(lpSizeL);
        }

Note that the code is identical up to and including the line that says "if (sz.cy
is greater than 20)". The new code also lacks the "TRACE" lines.

REFERENCES
==========


Additional query words: ocx

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Keywords          : kbole kbActiveX kbCOMt kbCtrl kbMFC kbVC420 kbVC500 kbVC600 kbDSupport kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : :4.2,4.2b,5.0,6.0
Issue type        : kbhowto

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