介绍asp.net 2.0的新特性。是《asp.net2.0应用开发技术》一书的延续。
在asp.net 2.0中，可以在数据绑定时，通过设置dropdownlist的appenddatabounditems属性为true,在数据绑定之前添加一个新的项目，并且这个新加的项目会保存在viewstate之中。下面就是一个实现的例子：
c#代码
<%[email protected] page language="c#" %>
<%[email protected] import namespace="system.data" %>
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional//en"
"http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
<script runat="server">...
icollection createdatasource()
...{
datatable dt = new datatable();
datarow dr;
dt.columns.add(new datacolumn("id", typeof(int32)));
dt.columns.add(new datacolumn("text", typeof(string)));
for (int i = 0; i < 6; i++)
...{
dr = dt.newrow();
dr[0] = i;
dr[1] = "列表项目 " + i.tostring();
dt.rows.add(dr);
}
dataview dv = new dataview(dt);
return dv;
}
protected void button1_click(object sender, eventargs e)
...{
response.write("<li>dropdownlist1 您选择的项目：" + dropdownlist1.selectedvalue
+ " ; " + dropdownlist1.selecteditem.text);
response.write("<li>dropdownlist2 您选择的项目：" + dropdownlist2.selectedvalue
+ " ; " + dropdownlist2.selecteditem.text);
}
protected void page_load(object sender, eventargs e)
...{
if (!ispostback)
...{
dropdownlist1.appenddatabounditems = true;
dropdownlist1.items.add(new listitem("-- 请选择一个选择项 --", ""));
dropdownlist2.datasource = dropdownlist1.datasource = createdatasource();
dropdownlist2.datatextfield = dropdownlist1.datatextfield = "text";
dropdownlist2.datavaluefield = dropdownlist1.datavaluefield = "id";
dropdownlist1.databind();
dropdownlist2.databind();
}
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>dropdownlist 补充例子</title>
</head>
<body>
<form id="form1" runat="server">
<asp:dropdownlist id="dropdownlist1" runat="server">
</asp:dropdownlist>
<asp:dropdownlist id="dropdownlist2" runat="server" appenddatabounditems="true">
<asp:listitem text="请选择" value=""></asp:listitem>
</asp:dropdownlist>
<asp:button id="button1" runat="server" text="得到选择的值" onclick="button1_click" />
</form>
</body>
</html>
vb.net代码
<%[email protected] page language="vb" autoeventwireup="true" %>
<%[email protected] import namespace="system.data" %>
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional//en"
"http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
<script runat="server">...
protected sub button1_click(byval sender as object, byval e as system.eventargs)
response.write("<li>dropdownlist1 您选择的项目：" + dropdownlist1.selectedvalue + _
" ; " + dropdownlist1.selecteditem.text)
response.write("<li>dropdownlist2 您选择的项目：" + dropdownlist2.selectedvalue + _
" ; " + dropdownlist2.selecteditem.text)
end sub
protected sub page_load(byval sender as object, byval e as system.eventargs)
if not ispostback then
dropdownlist1.appenddatabounditems = true
dropdownlist1.items.add(new listitem("-- 请选择一个选择项 --", ""))
dropdownlist2.datasource = createdatasource()
dropdownlist1.datasource = createdatasource()
dropdownlist2.datatextfield = "text"
dropdownlist1.datatextfield = "text"
dropdownlist2.datavaluefield = "id"
dropdownlist1.datavaluefield = "id"
dropdownlist1.databind()
dropdownlist2.databind()
end if
end sub
function createdatasource() as icollection
dim dt as datatable = new datatable()
dim dr as datarow
dt.columns.add(new datacolumn("id", gettype(system.int32)))
dt.columns.add(new datacolumn("text", gettype(string)))
for i as integer = 0 to 6
dr = dt.newrow()
dr(0) = i
dr(1) = "列表项目 " + i.tostring()
dt.rows.add(dr)
next
dim dv as dataview = new dataview(dt)
return dv
end function
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="head1" runat="server">
<title>dropdownlist 补充例子</title>
</head>
<body>
<form id="form1" runat="server">
<asp:dropdownlist id="dropdownlist1" runat="server">
</asp:dropdownlist>
<asp:dropdownlist id="dropdownlist2" runat="server" appenddatabounditems="true">
<asp:listitem text="请选择" value=""></asp:listitem>
</asp:dropdownlist>
<asp:button id="button1" runat="server" text="得到选择的值" onclick="button1_click" />
</form>
</body>
</html>
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