RequiredFieldValidator 控件

RequiredFieldValidator 控件确保必需字段不为空。它通常绑定到文本框以强制输入文本框。

控件的语法如下：

<asp:RequiredFieldValidator ID="rfvcandidate" 
   runat="server" ControlToValidate ="ddlcandidate"
   ErrorMessage="Please choose a candidate" 
   InitialValue="Please choose a candidate">
   
</asp:RequiredFieldValidator>