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Dynamically re-creating a combo box

, 2 Aug 2002
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Function to recreate a combo box at run-time to allow new styles, preserving its data

Introduction

Something which I frequently find myself needing to do is to switch a combo box to or from sorted. This is one reason (though not the main reason) I came up with my Dynamically Switchable Control. However, changing these styles after creation is something that combo-box does not support. This function presented here will recreate the combo box so that style changes take effect. The function will retain all list items, with item data, and the currently selected, or entered, text.

When the style is modified on a combobox to include or remove the CBS_SORT for example, it can be seen (by using GetStyle(), or using a tool such as Spy++) that the control does in fact have the new style, and yet the control's behaviour has not changed. The function here simply gets the current info from the control, i.e. styles, font etc, and recreates the control using these values.

How to use

I originally had a CComboBox-derived class which one member function to recreate the controls, but decided that this was more trouble than it was worth, as most of my combos derived from other things. Therefore I have presented this as a single function, which should be included in a global library file, so that you can invoke it on any combobox at any time.

In order to change the style of a combo, you should perform the usual method of setting the new style e.g.

combo.ModifyStyle(0, CBS_SORT);

and then after that call you should call:

RecreateComboBox(&combo)

The function takes an optional void pointer, lpParam, which is passed to CreateEx on recreating the control. If you have special requirements when creating your controls, and you normally pass in some data for the creation parameters, then you should pass the same info in here. Most developers can simply ignore this parameter.

The Function

The function to recreate the combo is below:

// recreate the combo box by copying styles etc, and list items
// and applying them to a newly created control
BOOL RecreateComboBox(CComboBox* pCombo, LPVOID lpParam/*=0*/)
{
	if (pCombo == NULL)
		return FALSE;
	if (pCombo->GetSafeHwnd() == NULL)
		return FALSE;

	CWnd* pParent = pCombo->GetParent();
	if (pParent == NULL)
		return FALSE;

	// get current attributes
	DWORD dwStyle = pCombo->GetStyle();
	DWORD dwStyleEx = pCombo->GetExStyle();
	CRect rc;
	pCombo->GetDroppedControlRect(&rc);
	pParent->ScreenToClient(&rc);	// map to client co-ords
	UINT nID = pCombo->GetDlgCtrlID();
	CFont* pFont = pCombo->GetFont();
	CWnd* pWndAfter = pCombo->GetNextWindow(GW_HWNDPREV);

	// get the currently selected text (and whether it is a valid list selection)
	CString sCurText;
	int nCurSel = pCombo->GetCurSel();
	BOOL bItemSelValid = nCurSel != -1;
	if (bItemSelValid)
		pCombo->GetLBText(nCurSel, sCurText);
	else
		pCombo->GetWindowText(sCurText);

	// copy the combo box items into a temp combobox (not sorted)
	// along with each item's data
	CComboBox comboNew;
	if (! comboNew.CreateEx(dwStyleEx, _T("COMBOBOX"), _T(""), 
                                 dwStyle, rc, pParent, nID, lpParam))
	  return FALSE;
	comboNew.SetFont(pFont);
	int nNumItems = pCombo->GetCount();
	for (int n = 0; n < nNumItems; n++)
	{
		CString sText;
		pCombo->GetLBText(n, sText);
		int nNewIndex = comboNew.AddString(sText);
		comboNew.SetItemData(nNewIndex, pCombo->GetItemData(n));
	}
	// re-set selected text
	if (bItemSelValid)
		comboNew.SetCurSel(comboNew.FindStringExact(-1, sCurText));
	else
		comboNew.SetWindowText(sCurText);

	// destroy the existing window, then attach the new one
	pCombo->DestroyWindow();
	HWND hwnd = comboNew.Detach();
	pCombo->Attach(hwnd);

	// position correctly in z-order
	pCombo->SetWindowPos(pWndAfter == NULL ? 
                                &CWnd::wndBottom : 
                               pWndAfter, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE);

	return TRUE;
}

See Also

History

  • Version 1 - 26 Jul 2002 - First version
  • Version 2 - 30 Jul 2002 - modified to include changes suggested by Jean-Michel LE FOL and Davide Zaccanti

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Paul Vickery
Software Developer (Senior)
United Kingdom United Kingdom
Originally from an electronics background, I moved into software in 1996, partly as a result of being made redundant, and partly because I was very much enjoying the small amount of coding (in-at-the-deep-end-C) that I had been doing!
 
I swiftly moved from C to C++, and learned MFC, and then went on to real-time C on Unix. After this I moved to the company for which I currently work, which specialises in Configuration Management software, and currently program mainly in C/C++, for Windows. I have been gradually moving their legacy C code over to use C++ (with STL, MFC, ATL, and WTL). I have pulled in other technologies (Java, C#, VB, COM, SOAP) where appropriate, especially when integrating with third-party products.
 
In addition to that, I have overseen the technical side of the company website (ASP, VBScript, JavaScript, HTML, CSS), and have also worked closely with colleagues working on other products (Web-based, C#, ASP.NET, SQL, etc).
 
For developing, I mainly use Visual Studio 2010, along with an in-house-designed editor based on Andrei Stcherbatchenko's syntax parsing classes, and various (mostly freeware) tools. For website design, I use Dreaweaver CS3.
 
When not developing software, I enjoy listening to and playing music, playing electric and acoustic guitars and mandolin.
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Comments and Discussions

 
GeneralThank you very mach! I have found it for long time.^_^ Pinmemberlibbyliugang13-May-08 7:15 
Generalthanx! Pinmembertortexy16-Jan-08 7:13 
GeneralThis is example PinmemberVC Spark19-Jun-07 23:14 
GeneralRe: This is example PinmemberVC Spark21-Jun-07 1:53 
GeneralRe: This is example PinmemberMikie2-Sep-09 4:25 
Generalthanks Pinmemberbizulk1-Sep-05 8:08 
GeneralControl Disappear PinsussJACCY24-Mar-05 4:11 
GeneralRe: Control Disappear PinmemberPaul S. Vickery26-Apr-05 3:49 
GeneralRe: Control Disappear PinmemberMarco F6-Oct-05 22:48 
AnswerRe: Control Disappear PinmemberMarco F6-Oct-05 22:55 
GeneralSuggestion .... PinmemberCheGueVerra5-Nov-04 10:49 
GeneralSlightly off-topic question: combo drop-down arrow PinmemberDavid Pritchard22-Sep-04 6:48 
GeneralRe: Slightly off-topic question: combo drop-down arrow PinmemberRich Frank6-Nov-04 13:32 
GeneralRe: Slightly off-topic question: combo drop-down arrow PinmemberDavid Pritchard7-Nov-04 6:01 
GeneralRe: Slightly off-topic question: combo drop-down arrow PinmemberDavid Pritchard7-Nov-04 16:40 
GeneralRe: Slightly off-topic question: combo drop-down arrow PinmemberRich Frank7-Nov-04 23:57 
GeneralRe: Slightly off-topic question: combo drop-down arrow PinmemberDavid Pritchard8-Nov-04 0:31 
QuestionIs it possible with ATL ? Pinmembersanpro25-Dec-03 3:51 
GeneralNo more vert. scrollbar PinsussSimon66614-Nov-02 0:09 
GeneralRe: No more vert. scrollbar PinsussSimon66614-Nov-02 0:16 
GeneralZOrder PinmemberDavide Zaccanti26-Jul-02 21:55 
GeneralRe: ZOrder PinmemberPaul S. Vickery30-Jul-02 3:06 

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