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我想实现这种功能：
如果用户再一个DropDownList里选了指定的项，那么就激发RequirdFieldValidator控件对一个TextBox里面得值进行非空验证，而如果选了其它的项的话就不验证。因为是在一个控件里进行条件判断的，所以好像不能用CauseValidate属性。而用CustomerValidator控件的话对于空值是默认正确的！！不知道各位有什么好的实现方法！
use client side javascript in WebUIValidation.js, for example, the following validates txt1 control when you select 2 from the dropdownlist:
<form runat="server">
<asp:TextBox id="txt1" runat="Server" />
<asp:RequiredFieldValidator id="val" ControlToValidate="txt1" ErrorMessage="required" runat="server" />
<asp:DropDownList id="DropDownList1" runat="server" onchange="testValid()">
<asp:ListItem Text="0" Value="0" />
<asp:ListItem Text="1" Value="1" />
<asp:ListItem Text="2" Value="2" />
<asp:ListItem Text="3" Value="3" />
</asp:DropDownList>
<asp:Button id="btn" Text="click me" runat="server"/>
</form>
<script language="javascript">
function testValid()
{
var dropdown = document.all("DropDownList1");
var validator = document.all("val");
if (dropdown.selectedIndex ==2)
{
validator.isvalid = validator.evaluationfunction(validator);
}
else
{
validator.isvalid = true;
}
ValidatorUpdateDisplay(validator);
}
</script>
