How to create custom control tool for textbox validation?

Question

我想创建一个像文本框验证这样的工具，那么如何在 asp.net c# 中创建文本框验证工具

Answer 1

<asp:Textbox id="txtLastName" runat="server"></asp:Textbox>
<asp:RequiredFieldValidator id="RequiredFieldValidator1" runat="server"
  ControlToValidate="txtLastName"
  ErrorMessage="Last name is a required field."
  ForeColor="Red">
</asp:RequiredFieldValidator>