带有标注扩展器的复选框列表的自定义验证器

Question

对此有些困难。来自代码的onServerValidate触发并设置args.IsValid = false但是自定义验证器没有弹出不会在客户端显示错误。我也试图使用AJAX标注扩展器来扩展它。

<asp:CustomValidator ID="cvOffenceList" runat="server" 
            ErrorMessage="Please check at least one item on the offence list." 
            Display="None" ForeColor="#CC0000" 
            onservervalidate="cvOffenceList_ServerValidate" 
            >*</asp:CustomValidator>
        <asp:ValidatorCalloutExtender ID="ValidatorCalloutExtender2" runat="server" 
            TargetControlID="cvOffenceList">
        </asp:ValidatorCalloutExtender>
        <asp:CheckBoxList ID="cbOffenceList" runat="server" >
            <asp:ListItem>Items1</asp:ListItem>
            <asp:ListItem>Items2</asp:ListItem>
            <asp:ListItem>Items3</asp:ListItem>
        </asp:CheckBoxList>

protected void cvOffenceList_ServerValidate(object source, ServerValidateEventArgs args)
{
    args.IsValid = false;
    // Iterate through the Checkbox List and see if any items are checked
    for (int j = 0; j < cbOffenceList.Items.Count; j++)
    {
        if (cbOffenceList.Items[j].Selected)
        {
            // If any item is checked then validation is set to true
            args.IsValid = true;
        }
    }
}

protected void btnSubmitCase_Click(object sender, EventArgs e)
{
    if (Page.IsValid)
    {
        // Store Session Variables for further use

        // Insert Case Info to Table

        // Check if Image has a file
    }
}