Using a Virtual CListView with a Dynaset

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;
} 



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