<asp:TextBox ID="TextBox1" runat="server" Height="51px" Width="161px"
Rows="10" TextMode="MultiLine"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server"
ForeColor="Red" text="用户名不能为空" ControlToValidate ="TextBox1"
></asp:RequiredFieldValidator>
原文：http://www.cnblogs.com/914556495wxkj/p/3554051.html