Q136302: FIX: Drop-down Combobox Does Not Move with Property Sheet
Article: Q136302
Product(s): Microsoft C Compiler
Version(s): WINDOWS:1.52,1.52b; winnt:2.0,2.1,2.2
Operating System(s):
Keyword(s): kbcode kbComboBox kbMFC kbPropSheet KbUIDesign kbVC152fix kbVC200fix kbVC210fix kbVC220
Last Modified: 08-MAY-2001
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The information in this article applies to:
- Microsoft Visual C++, versions 1.52, 1.52b, 2.0, 2.1, 2.2
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SYMPTOMS
========
When a combo box on the active page of a CPropertySheet object is opened and the
property sheet is moved by dragging it with the mouse, the drop-down portion of
the combo box stays at its current screen position; it does not move with the
underlying property sheet's dialog box.
NOTE: This bug consistently occurs in 16-bit applications running under Windows
95 or Windows version 3.x. However, it does not occur when running under Windows
NT, and it occurs intermittently in 32-bit applications running under Windows
95.
CAUSE
=====
The _AfxCancelModes internal MFC function is not called from
CPropertySheet::PreTranslateMessage() as it is for CFrameWnd. In 32-bit Visual
C++, _AfxCancelModes is defined as AfxCancelModes.
RESOLUTION
==========
To work around this problem, derive a class from CPropertySheet and call
_AfxCancelModes from the derived class's PreTranslateMessage when the
WM_LBUTTONDOWN or WM_NCLBUTTONDOWN messages are received. See the "Step- By-Step
Workaround" section in this article for an example.
STATUS
======
Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This problem was corrected in Microsoft Visual C++,
32-bit Edition, version 4.0.
MORE INFORMATION
================
Step-By-Step Workaround
-----------------------
1. Create a new class derived from CPropertySheet.
1. Open the ClassWizard.
2. Click the Add Class button.
3. Choose a Class Type of generic CWnd. This is necessary because ClassWizard
does not support creating a CPropertySheet class in 16-bit Visual C++. If
you are using 32-bit Visual C++, you should be able to derive a class from
CPropertySheet directly.
4. Enter a Class Name such as CMySheet.
5. Click the Create Class button.
2. If you are using 32-bit Visual C++, please skip steps 2.a, 2.b, and 2.c. In
the new .h file (mysheet.h), make these changes:
1. Change this:
class CMySheet : public CWnd
To this:
class CMySheet : public CPropertySheet
2. Add the following as the first line in the class definition:
DECLARE_DYNAMIC(CMySheet)
3. Delete the default constructor declaration and add the following two
constructors in its place:
CMySheet(UINT nIDCaption, CWnd *pParentWnd = NULL,
UINT iSelectPage = 0 ) : CPropertySheet(nIDCaption,
pParentWnd, iSelectPage) { }
CMySheet(LPCTSTR pszCaption, CWnd *pParentWnd = NULL,
UINT iSelectPage = 0 ) : CPropertySheet(pszCaption,
pParentWnd, iSelectPage) { }
4. Add a prototype for an override of PreTranslateMessage in a public section
of the class definition:
public:
virtual BOOL PreTranslateMessage(MSG* pMsg);
3. If you are using 32-bit Visual C++, please skip step 3.a. In the new .cpp
file (mysheet.cpp), make these changes:
1. Delete the default constructor function body.
2. Add the definition of PreTranslateMessage:
BOOL CMySheet::PreTranslateMessage(MSG* pMsg)
{
// check for special cancel modes for ComboBoxes
if (pMsg->message == WM_LBUTTONDOWN ||
pMsg->message == WM_NCLBUTTONDOWN)
_AfxCancelModes(pMsg->hwnd); // filter clicks
return CPropertySheet::PreTranslateMessage(pMsg);
}
3. Use The following sample code to define _AfxCanelModes. Place this code
should be placed above the CMySheet::PreTranslateMessage definition. The
code is needed because if the project is linking to the DLL version of
MFC, you need to copy the code for this function and one other function
that is called and insert it into the project. The code can be found in
msvc\mfc\src\winutil.cpp. If the project links to a static MFC library,
all you need to do is add a prototype for the function. The code handles
both situations by using the #ifdef - #else - #endif preprocessor
directives.
/* Compile options needed: Default AppWizard options
*/
#ifdef _AFXDLL // define the functions
BOOL PASCAL _AfxIsComboBoxControl(HWND hWnd, UINT nStyle)
{
if (hWnd == NULL)
return FALSE;
// do cheap style compare first
if ((UINT)(::GetWindowLong(hWnd, GWL_STYLE) & 0x0F) != nStyle)
return FALSE;
// do expensive classname compare next
// If using 16-bit Visual C++, use the following code
static char BASED_CODE szComboBox[] = "combobox";
char szCompare[sizeof(szComboBox) + 1];
::GetClassName(hWnd, szCompare, sizeof(szCompare));
// else if using 32-bit Visual C++, use the following code
// and comment out the code above.
//
// static const TCHAR szComboBox[] = _T("combobox");
// TCHAR szCompare[sizeof(szComboBox)/sizeof(szCompare[0])+1];
// ::GetClassName(hWnd, szCompare,
// sizeof(szCompare)/sizeof(szCompare[0]) );
return (lstrcmpi(szCompare, szComboBox) == 0);
}
void PASCAL _AfxCancelModes(HWND hWndRcvr)
{
// if we receive a message destined for a window, cancel any
// combobox popups that could be in toolbars or dialog bars
HWND hWndCancel = ::GetFocus();
if (hWndCancel == NULL)
return; // nothing to cancel
if (hWndCancel == hWndRcvr)
return; // let input go to window with focus
// focus is in part of a combo-box
if (!_AfxIsComboBoxControl(hWndCancel, (UINT)CBS_DROPDOWNLIST))
{
// try as a dropdown
hWndCancel = ::GetParent(hWndCancel);// parent of edit is combo
if (hWndCancel == hWndRcvr)
return; // let input go to part of combo
if (!_AfxIsComboBoxControl(hWndCancel, (UINT)CBS_DROPDOWN))
return; // not a combo-box that is active
}
// combo-box is active, but if receiver is a popup, do nothing
if (hWndRcvr != NULL &&
(::GetWindowLong(hWndRcvr, GWL_STYLE) & WS_CHILD) != 0 &&
::GetParent(hWndRcvr) == ::GetDesktopWindow())
return;
// finally, you should cancel the mode !
::SendMessage(hWndCancel, CB_SHOWDROPDOWN, FALSE, 0L);
}
#else // just prototype it
void PASCAL _AfxCancelModes(HWND hWndRcvr);
#endif
NOTE: In your application, make sure you use class CMySheet instead of the
default CPropertySheet.
Additional query words: 2.00 2.51 2.52 3.00 3.10 3.20
======================================================================
Keywords : kbcode kbComboBox kbMFC kbPropSheet KbUIDesign kbVC152fix kbVC200fix kbVC210fix kbVC220fix kbGrpDSMFCATL
Technology : kbVCsearch kbAudDeveloper kbVC220 kbVC200 kbVC210 kbVC152 kbVC152a
Version : WINDOWS:1.52,1.52b; winnt:2.0,2.1,2.2
Issue type : kbbug
Solution Type : kbfix
=============================================================================
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