Using a Virtual CListView with a Dynaset

CodeGuru content and product recommendations are editorially independent. We may make money when you click on links to our partners. Learn More.

This example illustrates how to use an Access database file
with an IE 4.0 virtual list view.

Download sample project 63KB.

Loading large amounts of data into a CListView derived class
is a very slow process, even when the data is maintained in
memory. Accessing data in a database slows the process down even
further. One of new features of a list view control is the
ability to load data when it is needed. Below are the steps
envolved.

You must have a version of COMCTL32.DLL that came with IE 3.0
or later.

Open up you database file.

Use your document object to open your database, and record
set. In this example I use a dynaset type recordset. This allows
me to set the relative record number of a recordset object’s
current record by using CDaoRecordSet’s SetAbsolutePosition
member function. Pass the a pointer to the recordset to your view
class in an appropriate manner.

BOOL CVirtualListDoc::OnOpenDocumentFile(LPCTSTR lpszPathname)
{
	CString m_FileName = lpszPathname;
	pDBase = new CDaoDatabase;
	pDBase->Open(m_FileName);
	CString strSQL = "SELECT * FROM TableName ORDER BY ColumnName";//Set up SQL statement
	pRecordSet = new CDaoRecordset(pDBase);
	pRecordSet->Open(dbOpenDynaset, strSQL);//Open recordset using SQL statement
	pRecordSet->MoveLast();//you have to access the records in the dynaset to get GCDaoRecordSet::etRecordCount() to work
}

Set the ListView’s style to LVS_OWNERDATA:

BOOL CVirtualListView::PreCreateWindow(CREATESTRUCT& cs)
{
	cs.lpszName = WC_LISTVIEW;
	cs.style &= ~LVS_TYPEMASK;
	cs.style |= LVS_REPORT;
	cs.style |= LVS_EDITLABELS;
	cs.style |= LVS_OWNERDATA;
	CListView::PreCreateWindow(cs);
}

Set number of items in list:

You have to tell the list view how many items it will contain.
This is done by sending a LVM_SETITEMCOUNT to the list control.
Do this and set up the list views columns in the views
OnInitialUpdate() member function. You can send a LVM_SETEXTENDEDLISTVIEWSTYLE message to the
control to set any of the new extended listview styles.

void CVirtualListView::OnInitialUpdate()
{
	CListView::OnInitialUpdate();
	/*set number of items in list to number of items in RecordSet*/

	/* create image list*/
	imageList.Create(IDB_IMAGELIST, 16, 1, RGB(0,0,0));
	GetListCtrl().SetImageList(&imageList, LVSIL_SMALL);

	/* set extended stlyes*/
	DWORD dwExStyle = LVS_EX_FULLROWSELECT | LVS_EX_GRIDLINES | /*LVS_EX_SUBITEMIMAGES |*/
						LVS_EX_HEADERDRAGDROP | LVS_EX_TRACKSELECT;
	GetListCtrl().SendMessage(LVM_SETEXTENDEDLISTVIEWSTYLE, 0, LPARAM(dwExStyle));

	LV_COLUMN lvColumn;
	lvColumn.mask = LVCF_FMT | LVCF_WIDTH | LVCF_TEXT | LVCF_SUBITEM;
	lvColumn.fmt = LVCFMT_LEFT;
	lvColumn.cx = 120;
	for(int i = 0; i < GetFieldCount(); i++) // set up columns
	{
		CDaoFieldInfo fieldinfo;
		pRecordSet->GetFieldInfo(i, fieldinfo);//get field name
		int len = fieldinfo.m_strName.GetLength();
		CString temp = fieldinfo.m_strName;
		TCHAR* szBuffer = new TCHAR[len + 1];
		strcpy(szBuffer, temp.GetBuffer(len));
		temp.ReleaseBuffer();
		lvColumn.pszText = szBuffer;
		GetListCtrl().InsertColumn(i, &lvColumn);//insert column
		delete szBuffer;
	}
	/*set number of items in ListView*/
	count = pRecordSet->GetRecordCount();//Get number of records
	GetListCtrl().SendMessage(LVM_SETITEMCOUNT, (WPARAM)count, (LPARAM)LVSICF_NOINVALIDATEALL);
}

Create a handler to handle
LVN_GETDISPINFO messages:

void CVirtualListViewView::OnGetDispInfo(NMHDR* pNMHDR, LRESULT* pResult)
{
	LV_DISPINFO* pDispInfo = (LV_DISPINFO*)pNMHDR;
	TCHAR szValue[MAX_PATH];
	COleVariant varValue;
	long index = pDispInfo->item.iItem;
	long subItem = 	pDispInfo->item.iSubItem;
	if(pDispInfo->item.mask & LVIF_TEXT)
	{
		try
		{
			pRecordSet->SetAbsolutePosition(index);//Set the file to desired index
		}
		catch(CDaoException* e)
		{
			return;
		}

		try
		{
			if(subItem)
				pRecordSet->GetFieldValue(subItem, varValue);
			else
				pRecordSet->GetFieldValue(0, varValue);
		}
		catch(CDaoException* e)
		{
			return;
		}

		const VARIANT* variant = LPCVARIANT(varValue);
		switch(variant->vt)
		{
			case VT_I2:{	wsprintf(szValue, "%d", variant->iVal);
							break;
					   }
			case VT_I4:{	wsprintf(szValue, "%d", variant->lVal);
							break;
					   }
			case VT_R4:{	wsprintf(szValue, "%f", variant->fltVal);
							break;
					   }
			case VT_R8:{	wsprintf(szValue, "%f", variant->dblVal);
							break;
					   }
			case VT_CY:{	COleCurrency c(varValue);
							CString s = c.Format();//ie. 1.00
							strcpy(szValue, s.GetBuffer(s.GetLength()));
							s.ReleaseBuffer();
							break;
					   }
			case VT_DATE:{	COleDateTime t(variant->date);
							CString s = t.Format( "%A, %B %d, %Y" );//Day of Week, Month Day, Year
							strcpy(szValue, s.GetBuffer(s.GetLength()));
							s.ReleaseBuffer();
							break;
						 }
			case VT_BSTR:{  CString str = V_BSTRT( &varValue );//convert BSTR to CString
							strcpy(szValue, str.GetBuffer(str.GetLength()));
							str.ReleaseBuffer();
							break;
						}
			case VT_BOOL:{	if(variant->boolVal)
								strcpy(szValue, "TRUE");
							else
								strcpy(szValue, "FALSE");
							break;
						 }
			case VT_UI1:{	strcpy(szValue, (char*)variant->bVal);
							break;
						}

			default: break;

		}

		lstrcpyn(pDispInfo->item.pszText, szValue, pDispInfo->item.cchTextMax);//set item text
	}

	if(pDispInfo->item.mask & LVIF_IMAGE)
		pDispInfo->item.iImage = 0;//set image to first in list

	*pResult = 0;
}