使用DropDownList的ASP.Net自定义验证器控件

以下代码用于使用Custom Validator验证DropDownList控件.

Default1.aspx

<td>
        <asp:DropDownList ID="DDL_Product" runat="server" Height="21px" Width="128px">
             <asp:ListItem>Select</asp:ListItem>
             <asp:ListItem>Nokia</asp:ListItem>
             <asp:ListItem>LG</asp:ListItem>
             <asp:ListItem>Samsung</asp:ListItem>
             <asp:ListItem>sony</asp:ListItem>
             <asp:ListItem>Micromax</asp:ListItem>
             <asp:ListItem>Karbonn</asp:ListItem>
             <asp:ListItem>Apple</asp:ListItem>
         </asp:DropDownList>
    </td>
    <td>
         <asp:CustomValidator ID="cv1" display="Dynamic" ControlTovalidate = "DDL_Product" OnServerValidate="ddl_server" runat="server" ForeColor="Red" ErrorMessage="Please Select the Product"></asp:CustomValidator>
    </td>

Default1.aspx.cs

protected void ddl_server(object sender,ServerValidateEventArgs e)
{
     if (e.Value.selectedindex <= 0)
     {
        e.IsValid = true;
     }
     else
     {
        e.IsValid = false;
     }
}

以上验证未经验证.
我不知道如何使用此控件并验证DropDownList.请更正错误.

解决方法

你应该使用RequireValidator.

1)添加“选择”项的值,将用于验证初始值：

<asp:DropDownList ID="DDL_Product" runat="server" Height="21px" Width="128px">
       <asp:ListItem Value="0">Select</asp:ListItem>
       /*Rest of items*/
</asp:DropDownList>

2)然后像这样使用RequireValidator,比较DDL的初始值：

<asp:requiredFieldValidator InitialValue="0" 
    ID="rfvDDL_Product" display="Dynamic" 
    ControlTovalidate="DDL_Product"
    runat="server"  Text="*" 
    ErrorMessage="Please Select the Product"
    ForeColor="Red">
</asp:requiredFieldValidator>

编辑：

有关解释,请访问MSDN：

CustomValidator Class

Use the CustomValidator control to provide a user-defined validation
function for an input control. The CustomValidator control is a
separate control from the input control it validates,which allows you
to control where the validation message is displayed.

RequiredFieldValidator Class

Use this control to make an input control a required field. The input control fails validation if its value does not change from the InitialValue property upon losing focus.