动态添加的dropdownlist的SelectedIndexChanged不执行

Question

动态生成的dropdownlist,绑定的selectedindexChanged事件不执行。怎么回事？
代码如下protected void Page_Load(object sender, EventArgs e)
        {        }
        protected void btnok_Click(object sender, EventArgs e)
        {
            DropDownList drop = new DropDownList();
            drop.ID = "drop1";
            drop.Items.Add(new ListItem("11111", "1"));
            drop.Items.Add(new ListItem("22222", "2"));
            drop.Items.Add(new ListItem("33333", "3"));
            drop.AutoPostBack = true;
            drop.SelectedIndexChanged += new EventHandler(drop_change);
            panel1.Controls.Add(drop);
        }
        public void drop_change(object sender, EventArgs e)
        {
            //设断点看了，这里一直不会执行
            DropDownList drop = (DropDownList)sender;
            Response.Write(drop.SelectedItem.Text);
        }
DropDownList

Answer 1

DropDownList的AutoPostBack属性是否设成了true？

Answer 2

这个属二次触发事件，请参考：
http://www.cnblogs.com/insus/archive/2012/10/09/2717420.html