加载大量数据到CListView派生类是一个非常慢的过程，甚至当数据在内存是也
是如此。在数据库中存取数据时就更慢了。一个列表视的新的特点是当它需要数
据是再加载的能力。下面是具体步骤。
你必须安装IE3以后版本的COMCTL32.DLL。
打开你的数据库文件。
使用你的文档对象打开你的数据库文件和记录集。在该例子中，我用了一个动
态集类型的记录集。这样就允许我使用CDaoRecordSet的SetAbsolutePosition
成员函数设置一个记录集对象的当前记录相对记录号。
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
}
设置该列表视的风格为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);
}
在列表中设置项的个数。
你需要告诉列表视将包括多少项。这通过发送一个LVN_SETITEMCOUNT到该列表控
制。在列表视的OnInitialUpdate()成员函数中来完成上述工作，并且设置列表
视的列数。你能够发送一个LVM_SETEXTENDLISTVIEWSTYLE消息给该控件来设置一
些新的扩展的列表视风格。
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);
}
建立LVN_GETDISPINFO消息的处理函数：
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;
}
文章来源于领测软件测试网 https://www.ltesting.net/
