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如何在datagrid绑定之前为dataset添加新列
在实际的应用中经常会遇到根据其它列计算某一新列的结果，实现这样的功能有两种办法：一个直接使用sql语句；另外就是在绑定时进行动态添加。第一种方法以前已经介绍过。下面就是第二种方法的具体实现：
adddatasetcolumn.aspx
<%@ page language="<a href="http://dev.21tx.com/language/vb/" target="_blank">vb</a>" autoeventwireup="false" codebehind="adddatasetcolumn.aspx.vb"
inherits="aspx<a href="http://dev.21tx.com/web/" target="_blank">web</a>.adddatasetcolumn"%>
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
<head>
<title>adddatasetcolumn</title>
<meta name="generator" content="microsoft visual studio <a href="http://dev.21tx.com/do.net/" target="_blank">.net</a> 7.1">
<meta name="code_language" content="visual basic .net 7.1">
<meta name="vs_defaultclientscript" content="<a href="http://dev.21tx.com/web/javascript/" target="_blank">javascript</a>">
<meta name="vs_targetschema" content="http://schemas.microsoft.com/intellisense/ie5">
</head>
<body ms_positioning="gridlayout">
<form id="form1" method="post" runat="server">
<asp:datagrid id="datagrid1" runat="server" autogeneratecolumns="false"
showfooter="true" width="100%">
<headerstyle font-names="宋体" font-bold="true" horizontalalign="center"
forecolor="navy" backcolor="lightsalmon"></headerstyle>
<footerstyle backcolor="#ffccff"></footerstyle>
<columns>
<asp:templatecolumn headertext="订单号">
<itemtemplate>
<asp:label id="orderid" runat="server"></asp:label>
</itemtemplate>
</asp:templatecolumn>
<asp:templatecolumn headertext="产品号">
<itemtemplate>
<asp:label id="productid" runat="server"></asp:label>
</itemtemplate>
</asp:templatecolumn>
<asp:templatecolumn headertext="单价">
<itemtemplate>
<asp:label id="unitprice" runat="server"></asp:label>
</itemtemplate>
</asp:templatecolumn>
<asp:templatecolumn headertext="数量">
<itemtemplate>
<asp:label id="quantity" runat="server"></asp:label>
</itemtemplate>
</asp:templatecolumn>
<asp:templatecolumn headertext="折扣">
<itemtemplate>
<asp:label id="discount" runat="server"></asp:label>
</itemtemplate>
</asp:templatecolumn>
<asp:templatecolumn headertext="总计">
<itemtemplate>
<asp:label id="lbltotal" runat="server"></asp:label>
</itemtemplate>
</asp:templatecolumn>
</columns>
</asp:datagrid>
</form>
</body>
</html>
adddatasetcolumn.aspx.vb
imports system.web.ui.webcontrols
public class adddatasetcolumn
inherits system.web.ui.page
#region " web 窗体设计器生成的代码 "
'该调用是 web 窗体设计器所必需的。
<system.diagnostics.debuggerstepthrough()> private sub initializecomponent()
end sub
protected withevents datagrid1 as system.web.ui.webcontrols.datagrid
'注意: 以下占位符声明是 web 窗体设计器所必需的。
'不要删除或移动它。
private designerplaceholderdeclaration as system.object
private sub page_init(byval sender as system.object, byval e as system.eventargs) handles mybase.init
'codegen: 此方法调用是 web 窗体设计器所必需的
'不要使用代码编辑器修改它。
initializecomponent()
end sub
#end region
private sub page_load(byval sender as system.object, byval e as system.eventargs) handles mybase.load
dim strcnn as string = "data source=..netsdk; initial catalog=northwind;user id=sa;password=;"
dim ocn as new system.data.sqlclient.sqlconnection(strcnn)
dim strsql as system.string = "select * from [order details]"
dim ds as system.data.dataset = new system.data.dataset
ocn.open()
dim da as system.data.sqlclient.sqldataadapter = new system.data.sqlclient.sqldataadapter(strsql, ocn)
' 可以直接使用sql语句实现，这个方法可以直接绑定，不需要用模板即可
' cmd.commandtext = "select *,unitprice * quantity *(1- discount) as total from [order details]"
' 我们使用另外一种方法，在datagrid绑定之前为dataset添加一个列
da.fill(ds, "ds")
dim dvwgrid as dataview = ds.tables(0).defaultview
datagrid1.datasource = dvwgrid
datagrid1.databind()
ocn.close()
ocn.dispose()
end sub
private sub datagrid1_itemdatabound(byval sender as object, byval e as datagriditemeventargs) _
handles datagrid1.itemdatabound
dim elemtype as listitemtype = e.item.itemtype
if (elemtype = listitemtype.item or elemtype = listitemtype.alternatingitem) then
'把dataitem转换回datarowview对象
dim mydatarowview as datarowview = ctype(e.item.dataitem, datarowview)
dim mydatarow as datarow = mydatarowview.row
ctype(e.item.cells(0).findcontrol("orderid"), label).text = mydatarow("orderid")
ctype(e.item.cells(1).findcontrol("productid"), label).text = mydatarow("productid")
ctype(e.item.cells(2).findcontrol("unitprice"), label).text = mydatarow("unitprice")
ctype(e.item.cells(3).findcontrol("quantity"), label).text = mydatarow("quantity")
ctype(e.item.cells(4).findcontrol("discount"), label).text = mydatarow("discount")
dim dblprice as double = double.parse(mydatarow("unitprice"))
dim intquantity as integer = int32.parse(mydatarow("quantity"))
dim intdiscount as double = double.parse(mydatarow("discount"))
dim ntotal as string = string.format("{0:c}", dblprice * (1 - intdiscount) * intquantity)
ctype(e.item.cells(5).findcontrol("lbltotal"), label).text = ntotal
end if
end sub
end class
