When developing an OLE Control, you may decide that some of the properties
should be serialized. This can be accomplished in the DoPropExchange()
method of your COleControl-derived class by using the PX_ functions. The
PX_ functions also allow you to specify a default value for the property,
which is good programming practice. You may also want to give default
values to any stock properties that are used by your control. The
serialization and initialization of stock properties is handled by MFC in
COleControl::DoPropExchange(pPX). To set a default value for a stock
property, you need to work around some of MFC's functionality. This article
explains how to do it.
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When you use the Microsoft Control Developer's Kit (CDK) to create the MFC
framework for an OLE Control, it creates a COleControl-derived class with
an overridden DoPropExchange() member function. By default, the overridden
DoPropExchange() calls COleControl::DoPropExchange(). This in turn calls
COleControl::ExchangeStockProps(), which contains the MFC code for
serializing stock properties.
Within this function, MFC uses the COleControl m_dwStockPropMask protected
member variable to determine which stock properties you have added with
Class Wizard. This mask can be modified in your DoPropExchange() to force
MFC to ignore existing stock properties and therefore allow you to add your
own code. Ideally you should copy the relevant code already present in
COleControl::ExchangeStockProps(), and then modify it as necessary.
The following sample code shows how to accomplish this for the Caption
stock property by modifying step three of the Circ OLE Control tutorial.
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Sample Code
// MANUAL CONTROL OF MAKING Caption PERSISTANT.
// To test the initialization of the caption stock property
// replace the circle3 samples DoPropExchange function with the
// following version.
// These #defines can be found in the ..\Msvc20\Cdk32\Src\Ctlprop.cpp
// file and are given here to remove the need to continually track them
// down. In the code, only STOCKPROP_CAPTION is used.
#define STOCKPROP_BACKCOLOR 0x00000001
#define STOCKPROP_CAPTION 0x00000002
#define STOCKPROP_FONT 0x00000004
#define STOCKPROP_FORECOLOR 0x00000008
#define STOCKPROP_TEXT 0x00000010
#define STOCKPROP_BORDERSTYLE 0x00000020
#define STOCKPROP_ENABLED 0x00000040
void CCirc3Ctrl::DoPropExchange(CPropExchange* pPX)
{
ExchangeVersion(pPX, MAKELONG(_wVerMinor, _wVerMajor));
BOOL bLoading = pPX->IsLoading();
CString strText;
if (!bLoading)
strText = InternalGetText();
PX_String(pPX,_T("Caption"),strText,_T("Caption"));
if (bLoading) {
TRY
SetText(strText);
END_TRY
}
// Mask out the Caption stock property before
// calling the base class functionality.
m_dwStockPropMask &= ~STOCKPROP_CAPTION;
// Call the base class.
COleControl::DoPropExchange(pPX);
// Mask the Caption property bit back in to minimize
// possible side effects.
m_dwStockPropMask |= STOCKPROP_CAPTION;
if (pPX->GetVersion() == (DWORD)MAKELONG(_wVerMinor, _wVerMajor))
{
PX_Bool(pPX, _T("CircleShape"), m_circleShape, TRUE);
PX_Short(pPX, _T("CircleOffset"), m_circleOffset, 0);
PX_Long(pPX, _T("FlashColor"), (long &)m_flashColor,
RGB(0xFF, 0x00, 0x00));
PX_String(pPX, _T("Note"), m_note, _T("Note"));
}else if (pPX->IsLoading()) {
m_circleShape = TRUE;
m_circleOffset = 0;
m_flashColor = RGB(0xFF, 0x00, 0x00);
m_note = _T("");
}
}
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The functions discussed in this article can be found using the Find in
Files feature of Visual C++; in version 2.x within the Cdk32\Src directory
and in version 4.x within the mfc\src subdirectory.
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