Ensure (partial) visibility of a column

The following function ensures that a column is at least partially visible. Rex Myer provided a comparable function in his article “Multiline editable subitems”, but his code relies on the list having an item with index 0, it steps through all columns to find the left border and finally, if a column overlaps the right border by just one pixel but still has a 200 pixel distance from the left, the column will be moved to the left border. Additionally, the following code provides the bPartialOK-Flag known from CListCtrl::EnsureVisible(). Usage should be pretty much obvious 🙂

This code was developed with VC++ 5.0 (SP3), Windows NT 4.0 (SP3) and the new COMCTL32.DLL (v4.72)

bool CMyListCtrl::EnsureColumnVisible(int nColumn, bool bPartialOK)
{
	CHeaderCtrl* pHeader = reinterpret_cast(GetDlgItem(0));
	ASSERT(pHeader->IsKindOf(RUNTIME_CLASS(CHeaderCtrl)));

	CRect rcHeader;
	Header_GetItemRect(pHeader->m_hWnd, nColumn, &rcHeader);

	CRect rcClient;
	GetClientRect(&rcClient);

	int nOffset = GetScrollPos(SB_HORZ);

	if(bPartialOK)
	{
		if((rcHeader.left - nOffset < rcClient.right) && (rcHeader.right - nOffset > 0))
		{
			return true;
		}
	}

	int nScrollX = 0;

	if((rcHeader.Width() > rcClient.Width()) || (rcHeader.left - nOffset < 0))
	{
		nScrollX = rcHeader.left - nOffset;
	}
	else if(rcHeader.right - nOffset > rcClient.right)
	{
		nScrollX = rcHeader.right - nOffset - rcClient.right;
	}

	if(nScrollX != 0)
	{
		CSize size(nScrollX, 0);
		Scroll(size);
	}

	return true;
}