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   <TITLE>CListCtrl - Disable clicking on selected report view columns</TITLE>
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<FONT COLOR="#AOAO99">Disable clicking on selected report view columns</FONT></H3></CENTER>

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<p>This article was contributed by <a href="mailto:Petr.Novotny@antek.cz">Petr Novotny</a></p>

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<p>I have developed a short piece of code to disable clicking column 
headers for columns than cannot be sorted-by.</p>


<p>This code simply uses the customization of header control as 
presented in "Indicating sort order" article. I just added slight 
more functionality to that header control.</p>

<p>1. I define a prototype and a variable in a class declaration body:</p>

<pre><tt><FONT COLOR="#990000">
public:
	typedef BOOL (*ColumnCheckF)(void *,int,LPARAM);

	void SetCallback(ColumnCheckF checkf=NULL,void * cbdata=NULL)
	{
		m_fColumnCheck=checkf;
		m_pCBData=cbdata;
	}

private:
	ColumnCheckF m_fColumnCheck;
	void *m_pCBData;
</tt></pre></font>

<p>After a click in a header, I find out the column (and I try to be 
wise and not disable clicking to resize columns) and ask the callback 
if the click is allowed (TRUE returned) or not.</p>

<p>It means, in the header (class declaration), I add</p>

<tt><pre><FONT COLOR="#990000">
	// handlers
	afx_msg void OnLButtonDown(UINT,CPoint);
	DECLARE_MESSAGE_MAP()
</tt></pre></font>

<p>and in the .CPP I add</p>

<tt><pre><FONT COLOR="#990000">
BEGIN_MESSAGE_MAP(CCustHeaderCtrl,CHeaderCtrl)
	ON_WM_LBUTTONDOWN()
END_MESSAGE_MAP()

void CCustHeaderCtrl::OnLButtonDown(UINT flags,CPoint pt)
{
	if (m_fColumnCheck!=NULL)
	{
		HD_ITEM hditem;
		CClientDC dc(this);
		int offset=dc.GetTextExtent(_T(" "),1).cx*2;
		int x_coord=pt.x;

		int column=0;
		hditem.mask=HDI_WIDTH;
		while (x_coord&gt;((column==0)?0:offset))
		{
			GetItem(column,&hditem);
			if (x_coord&lt;hditem.cxy-offset)
			{
				// falls inside - query the func
				hditem.mask=HDI_LPARAM;
				GetItem(column,&amp;hditem);
				if (!m_fColumnCheck(m_pCBData,column,hditem.lParam))
				{
					// don't forward the message!
					return;
				}
				break;
			}
			
			x_coord-=hditem.cxy;
			column++;
		}
	}

	CHeaderCtrl::OnLButtonDown(flags,pt);
}
</tt></pre></font>

<p>The side effect of this code - it disables dragging the "disabled"
columns. (That's because the header control never hears of LButtonDown
message - I filter it of.)</p>


<P>Posted on: April 14, 98.
<P>
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