自定义控件 动态创建的文本框取值的问题

Question

代码如下：TextBox tb = new TextBox(); tb.ID = "txtIndex";pnPager.Controls.Add(tb); TextBox txtIndex = new TextBox(); txtIndex = pnPager.FindControl("txtIndex") as TextBox; pnPager.Controls.Add(txtIndex);  if (txtIndex.Text == "")。。。 为什么txtIndex的值永远为空？