如果在这种情况下动态添加控件，则需要自己保留控件的状态.有关更多详细信息，请查看以下文章.

在ASP.NET应用程序中为动态创建的控件保留状态 [

If you add control dynamically in that case you need to preserve the state of the control by yourself. For more details you can check following article.

Retaining State for Dynamically Created Controls in ASP.NET applications[^]

The other way around is to get the values of the control from Request.Form["ControlName"]