How to add Horizontal Extent handling for a CListBox

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The following code illustrates how to implement Horizonal Extent handling
for a CListBox. For more information you can look at Q66370.
This class implements a derived CListBox which automatically sets the
horizontal extent.

CListBoxEx.h

//

// CListBoxEx.h     v1.1

//

#ifndef _LISTBOX_EX_H

#define _LISTBOX_EX_H
#include 
class CListBoxEx : public CListBox

{

public:

     //virtual functions

     virtual int AddString( LPCTSTR sString );

     virtual int DeleteString( UINT nIndex );

     virtual int InsertString( int nIndex, LPCTSTR lpszItem );

     virtual void ResetContent();

     virtual int Dir( UINT attr, LPCTSTR lpszWildCard );
private:

     //helpers

     LONG GetExtentForString( LPCTSTR sText );

     long GetExtentForEntireControl();

};
#endif




CListBoxEx.cpp


// CListBoxEx.cpp   v1.0
//

#include "stdafx.h"
#include "listboxex.h"


//
// see Q66370 for more information
//

///////////////////////////////////////////////////////////////////////////
///////
//
//override functions
///////////////////////////////////////////////////////////////////////////
///////

int CListBoxEx::AddString(LPCTSTR lpszItem)
{

     LONG lStringExtent = GetExtentForString(lpszItem);
     if(GetHorizontalExtent() < lStringExtent)
        SetHorizontalExtent(lStringExtent);

     return CListBox::AddString(lpszItem);
}

int CListBoxEx::DeleteString( UINT nIndex )
{
     int nCountLeft=CListBox::DeleteString(nIndex);
     if (nCountLeft== LB_ERR)
         return LB_ERR;

      LONG lMaxExtent=GetExtentForEntireControl();
      SetHorizontalExtent(lMaxExtent);

      return nCountLeft;
}

int CListBoxEx::InsertString( int nIndex, LPCTSTR lpszItem )
{
      int nInsertPos=InsertString(nIndex, lpszItem);
      if (nInsertPos== LB_ERR)
           return LB_ERR;

      LONG lStringExtent=GetExtentForString(lpszItem);
      if(GetHorizontalExtent() < lStringExtent)
           SetHorizontalExtent(lStringExtent);

      return nInsertPos;
}

void CListBoxEx::ResetContent()
{
      SetHorizontalExtent(0);
      CListBox::ResetContent(); return;
}

int CListBoxEx::Dir( UINT attr, LPCTSTR lpszWildCard )
{
     int nReturn=Dir(attr, lpszWildCard );
     if (nReturn== LB_ERR || nReturn== LB_ERRSPACE)
         return nReturn;

     LONG lMaxExtent=GetExtentForEntireControl();
     SetHorizontalExtent(lMaxExtent);
     return nReturn;
}
////////////////////////////////////////////////////////////////////////////////// 
//helper functions 
////////////////////////////////////////////////////////////////////////////////// 

LONG CListBoxEx::GetExtentForString(LPCTSTR lpszItem)
{
    CDC* cdc=this->GetDC();
    CFont* font = this->GetFont();
    CFont* pOldFont;

    if (font)
     {
        pOldFont = cdc->SelectObject(font);

          TEXTMETRIC tm;
          cdc->GetTextMetrics(&tm);

          CSize size = cdc->GetTextExtent(lpszItem, lstrlen(lpszItem) );
          size.cx += tm.tmAveCharWidth;

          cdc->SelectObject(pOldFont);
          this->ReleaseDC(cdc);

          return (LONG) size.cx;
     }

     this->ReleaseDC(cdc);

     return 0L;
}

long CListBoxEx::GetExtentForEntireControl()
{
	CDC* cdc = this->GetDC();
	CFont* font = this->GetFont();
	CFont* pOldFont;
	if (font)
	{
		pOldFont = cdc->SelectObject(font);
		TEXTMETRIC tm;
		cdc->GetTextMetrics(&tm);
		CString sText;
		LONG max_cx = 0;

/****----------------C H A N G E---REY--8/29/98----------****
 ****		for(int n = 0; n<=GetCount(); n++)
 ****----------------------------------------------------****/
		for(int n = 0; n<GetCount(); n++)
/****--------------------END CHANGE----------------------****/
		{
			this->GetText(n, sText);
			if (sText == "")
				continue;
			CSize size = cdc->GetTextExtent(sText, sText.GetLength());
			size.cx += tm.tmAveCharWidth;
			if(max_cx <= size.cx)
				max_cx = size.cx;
		}
		cdc->SelectObject(pOldFont);
		this->ReleaseDC(cdc);
		return max_cx;
	}
	this->ReleaseDC(cdc);
	return 0L;
}


BUGFIX (28 June 1998): In function GetExtentForEntireControl()

changed SText = "" ro SText == "".  
BUGFIX (4 Oct. 1998): In function GetExtentForEntireControl()

modify for loop statement to fix Assertion error that occurs when

you delete a string from the listbox.
Last updated: 11 November 1998
Comments:

Bug in Dir – Ken Sutherland (2000/01/06)
Bug in InsertString – Catherine Pelham (1999/11/18)
MUCH EASIER !!! – Use CListCtrl control instead. – Etti Malka (1999/08/12)
Only recalculate when deleting longest string – Glenn Brude (1999/05/19)
Cache longest value – Andrew Lazarus (1998/11/18)
BUG: incorrect calculating of text extent – Daniel Bernhard (1998/10/21)
BUG: GetExtentForEntireControl() does not work – Lin Sebastian Kayser (1998/10/08)
BUG when using tabstop – Michal Levi (1998/09/27)