验证控件的例子 -- 后面有个一简单的，最好加上ValidationSummary1，牛腩新闻也说过

    <form id="form1" runat="server">
    <p>
        <asp:Label ID="Label1" runat="server" Text="姓名："></asp:Label>
        <asp:TextBox ID="txtname" runat="server"></asp:TextBox>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" 
            ControlToValidate="txtname" ErrorMessage="*" ForeColor="#FF0066"></asp:RequiredFieldValidator>
        <asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" 
            ControlToValidate="txtname" ErrorMessage="长度在3-10之间" 
            ValidationExpression="\w{3,10}"></asp:RegularExpressionValidator>
    </p>
    <p>
        <asp:Label ID="Label2" runat="server" Text="密码："></asp:Label>
        <asp:TextBox ID="txtapwd" runat="server"></asp:TextBox>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" 
            ControlToValidate="txtapwd" ErrorMessage="*" ForeColor="#FF0066"></asp:RequiredFieldValidator>
        <asp:RegularExpressionValidator ID="RegularExpressionValidator2" runat="server" 
            ControlToValidate="txtapwd" ErrorMessage="长度在3-10之间" 
            ValidationExpression="\w{3,10}"></asp:RegularExpressionValidator>
    </p>
    <p>
        <asp:Label ID="Label3" runat="server" Text="再次密码："></asp:Label>
        <asp:TextBox ID="Cpwd" runat="server"></asp:TextBox>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" 
            ControlToValidate="Cpwd" ErrorMessage="*" ForeColor="#FF0066"></asp:RequiredFieldValidator>
        <asp:CompareValidator ID="CompareValidator1" runat="server" 
            ControlToCompare="txtapwd" ControlToValidate="Cpwd" ErrorMessage="两次密码要一样"></asp:CompareValidator>
    </p>
     <p>
        <asp:Label ID="Label7" runat="server" Text="邮箱："></asp:Label>
        <asp:TextBox ID="txtamail" runat="server"></asp:TextBox>
         <asp:RegularExpressionValidator ID="RegularExpressionValidator3" runat="server" 
             ControlToValidate="txtamail" ErrorMessage="邮箱格式不对" 
             ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"></asp:RegularExpressionValidator>
    </p>
    <p>
        <asp:Label ID="Label4" runat="server" Text="生日："></asp:Label>
        <asp:TextBox ID="txtbir" runat="server"></asp:TextBox>
        <asp:CompareValidator ID="CompareValidator2" runat="server" 
            ControlToValidate="txtbir" ErrorMessage="日期格式不对。" Operator="DataTypeCheck" 
            Type="Date"></asp:CompareValidator>
    </p>
    <p>
        <asp:Label ID="Label5" runat="server" Text="毕业日期："></asp:Label>
        <asp:TextBox ID="txtgread" runat="server"></asp:TextBox>
        <asp:CompareValidator ID="CompareValidator3" runat="server" 
            ControlToValidate="txtgread" Display="Dynamic" ErrorMessage="日期格式不对。" 
            Operator="DataTypeCheck" Type="Date"></asp:CompareValidator>
        <asp:CompareValidator ID="CompareValidator4" runat="server" 
            ControlToCompare="txtbir" ControlToValidate="txtgread" Display="Dynamic" 
            ErrorMessage="毕业不能在出生前面" Operator="GreaterThan" Type="Date"></asp:CompareValidator>
        <asp:CompareValidator ID="CompareValidator5" runat="server" 
            ControlToValidate="txtgread" Display="Dynamic" ErrorMessage="毕业日期大于当前日期" 
            Operator="LessThan" Type="Date"></asp:CompareValidator>
    </p>
    <p>
        <asp:Label ID="Label6" runat="server" Text="性别："></asp:Label>
        <asp:DropDownList ID="ddlage" runat="server">
            <asp:ListItem>---请输入性别---</asp:ListItem>
            <asp:ListItem>男</asp:ListItem>
            <asp:ListItem>女</asp:ListItem>
        </asp:DropDownList>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator4" runat="server" 
            ControlToValidate="ddlage" ErrorMessage="*" ForeColor="#FF0066" 
            InitialValue="---请输入性别---"></asp:RequiredFieldValidator>
    </p>
    <p><asp:Label ID="Label8" runat="server" Text="月："></asp:Label>
      <asp:TextBox ID="txtyue" runat="server"></asp:TextBox>
        <asp:RangeValidator ID="RangeValidator1" runat="server" 
            ControlToValidate="txtyue" ErrorMessage="1-12" MaximumValue="12" 
            MinimumValue="1" Type="Integer"></asp:RangeValidator>
    </p>
     <p><asp:Label ID="Label9" runat="server" Text="日："></asp:Label>
      <asp:TextBox ID="txtri" runat="server"></asp:TextBox>
        <asp:CompareValidator ID="CompareValidator7" runat="server" 
             ErrorMessage="月份不对，必须是数字" ControlToValidate="txtri" Operator="DataTypeCheck" 
             Type="Integer"></asp:CompareValidator>
         <asp:CustomValidator ID="CustomValidator1" runat="server" 
             ControlToValidate="txtri" ErrorMessage="29天。30天，31天分清楚哈" 
             onservervalidate="CustomValidator1_ServerValidate"></asp:CustomValidator>
    </p>
    <p>
    <asp:Button ID="Button1" runat="server" Text="Button"></asp:Button>
    </p>
    </form>

服务器

  protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                CompareValidator5.ValueToCompare = DateTime.Now.ToShortDateString();
            }
        }

        protected void CustomValidator1_ServerValidate(object source, ServerValidateEventArgs args)//自定义的控件代码
        {
            int yue = Convert.ToInt32(txtyue.Text.Trim());
            int ri = Convert.ToInt32(args.Value);
            int[] data = new int[] {31,29,31,30,31,30,31,31,30,31,30,31 };
            int day = data[yue-1];
            args.IsValid = (ri>=1&&ri<=day);
        }

客户端

   <script type="text/javascript">
        function must1(src, args) {
            var txtyue = document.getElementById("<%=txtyue.ClientID %>>");
             var yue = parseInt(txtyue.value,10);
             var ri = parseInt(args.Value,10);
             var data = new int[] {31,29,31,30,31,30,31,31,30,31,30,31 };
             var day = data[yue-1];
             args.IsValid = (ri>=1&&ri<=day);

        }
 

  


很简单的例子------------ValidationSummary1，牛腩新闻也说过

   <form id="form1" runat="server">
    
    <p>
    <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" 
            ControlToValidate="TextBox1" ErrorMessage="很长的错误信息这里写" ForeColor="#CC00FF">*</asp:RequiredFieldValidator>
   </p>
   <p>
    <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
       <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" 
           ControlToValidate="TextBox2" ErrorMessage="很长的错误信息" ForeColor="#990000">*提示一下</asp:RequiredFieldValidator>
    </p>
    <p>
    <asp:Button ID="Button1" runat="server" Text="Button" />
    </p>
    <asp:ValidationSummary ID="ValidationSummary1" runat="server" />
    </form>