javascript判断是否有对RadioButtonList选项选择

写javascript来判断是否有对radiobuttonlist选项选择，效果如下：

准备好radiobuttonlist数据源：
cosmetic.vb

imports microsoft.visualbasic
namespace insus.net
public class cosmetic
private _id as integer
private _type as string
private _name as string
private _weight as decimal
private _um as string
public property id as integer
get
return _id
end get
set(value as integer)
_id = value
end set
end property
public property type as string
get
return _type
end get
set(value as string)
_type = value
end set
end property
public property name as string
get
return _name
end get
set(value as string)
_name = value
end set
end property
public property weight as decimal
get
return _weight
end get
set(value as decimal)
_weight = value
end set
end property
public property um as string
get
return _um
end get
set(value as string)
_um = value
end set
end property
public sub new()
end sub
public sub new(id as integer, type as string, name as string, weight as decimal, um as string)
me._id = id
me._type = type
me._name = name
me._weight = weight
me._um = um
end sub
public function getdata() as list(of cosmetic)
dim o as new list(of cosmetic)
dim c as new cosmetic(1, "滋润霜", "玉兰油", 50, "g")
o.add(c)
dim c1 as new cosmetic(2, "滋润霜", "雅诗兰黛", 100, "g")
o.add(c1)
dim c2 as new cosmetic(3, "滋润霜", " 兰蔻", 80, "g")
o.add(c2)
dim c3 as new cosmetic(4, "滋润霜", "欧莱雅", 60, "g")
o.add(c3)
dim c4 as new cosmetic(5, "滋润霜", "芭比波朗", 120, "g")
o.add(c4)
return o
end function
end class

end namespace

在aspx放一个radiobuttonlist控件和一个铵钮：

化妆品：<asp:radiobuttonlist id="radiobuttonlistcosmetic" runat="server" repeatcolumns="10" repeatdirection="horizontal"></asp:radiobuttonlist>
<br />
<asp:button id="button1" runat="server" text="select" />

在aspx.vb中，为radiobuttonlist绑定数据源，当然绑定数据源下面的代码中，还得引用命名空间 imports insus.net

protected sub page_load(sender as object, e as eventargs) handles me.load
if not ispostback then
data_binding()
end if
end sub
private sub data_binding()
dim objcosmetic as new cosmetic()
me.radiobuttonlistcosmetic.datasource = objcosmetic.getdata()
me.radiobuttonlistcosmetic.datatextfield = "name"
me.radiobuttonlistcosmetic.datavaluefield = "id"
me.radiobuttonlistcosmetic.databind()
end sub

接下来是演示开始，写javascript代码：

view code
<script type="text/javascript">
function checkisselected() {
var rbl = document.getelementbyid("<%=radiobuttonlistcosmetic.clientid%>");
var radio = rbl.getelementsbytagname("input");
var isselect = false;
for (var i = 0; i < radio.length; i++) {
if (radio[i].checked) {
isselect = true;
break;
}
}
if (!isselect) {
alert("请选择一个选项。");
}
return isselect;
}
</script>

最后是为铵钮button写客户端事件

<asp:button id="button1" runat="server" text="select" onclientclick="return checkisselected()" />