ASP.NET 用户控件动态链接按钮不在回发Page_Load的控件中

我在UserControl中添加了一个动态链接按钮。在回发时，将显示动态控件，但控件集合的长度为 0。

namespace TestUC1
{
    public partial class UC : System.Web.UI.UserControl
    {
        public event EventHandler Click;
        protected void Page_Load(object sender, EventArgs e)
        {
            if (Page.IsPostBack) 
            {
                foreach (Control c in Controls)
                {
                    if (c is LinkButton)
                    {
                        ((LinkButton)c).Click += new EventHandler(OnClick);
                    }
                }
            } else
            {
                AddNewButton();
            }
        }
        protected void AddNewButton()
        {
            LinkButton lb = new LinkButton();
            lb.ID = "TestLink";
            lb.Text = "Test Link";
            lb.Click += new EventHandler(OnClick);
            Controls.Add(lb);
        }
        protected void OnClick(object sender, EventArgs e)
        {
            if (Click != null)
            {
                Click(this, new EventArgs());
            }
        }
    }
}