先看看网友的问题：

根据Asp.NET的机制，在html markup有写DropDownList控件与动态加载的控件有点不一样。如果把DropDownList控件写在html markup，即.aspx网页，网友的代码是没有问题的。但是，如果是在.aspx.cs动态加载的控件，那就不能使用Page_Load事件内加载，如果以此加载，就算是使用AutoPostBack = true也没有效果。
正确做法是在Page_Init事件中加载。


下面动态实时操作中，首先是运行网友的代码，确定无法运行。然后Insus.NET把Page_Load事件以及Showpage方法Comment out之后，并把动态产生DropDownList控件拷贝至page_Init事件。最后奇迹发生，能正确运行了。



演示中的代码：

protected void Page_Init(object sender, EventArgs e)    {        DropDownList ddl = new DropDownList();        ddl.AutoPostBack = true;        ddl.Items.Add(new ListItem("国家", "c"));        ddl.Items.Add(new ListItem("中國", "c1"));        ddl.Items.Add(new ListItem("美國", "c2"));        ddl.SelectedIndexChanged += new EventHandler(ddl_SelectedIndexChanged);        this.Form.Controls.Add(ddl);     }            protected void Page_Load(object sender, EventArgs e)    {        //if (!IsPostBack)        //{        //    ShowPage();        //}    }    //public void ShowPage()    //{    //    DropDownList ddl = new DropDownList();    //    ddl.AutoPostBack = true;    //    ddl.Items.Add(new ListItem("国家", "c"));    //    ddl.Items.Add(new ListItem("中國", "c1"));    //    ddl.Items.Add(new ListItem("美國", "c2"));    //    ddl.SelectedIndexChanged += new EventHandler(ddl_SelectedIndexChanged);    //    this.Form.Controls.Add(ddl);    //}    protected void ddl_SelectedIndexChanged(object sender, EventArgs e)    {        DropDownList dl = (DropDownList)sender;        Response.Write("<script>alert(‘" + dl.SelectedValue + "‘)</script>");    }

protected void Page_Init(object sender, EventArgs e)    {        DropDownList ddl = new DropDownList();        ddl.AutoPostBack = true;        ddl.Items.Add(new ListItem("国家", "c"));        ddl.Items.Add(new ListItem("中國", "c1"));        ddl.Items.Add(new ListItem("美國", "c2"));        ddl.SelectedIndexChanged += new EventHandler(ddl_SelectedIndexChanged);        this.Form.Controls.Add(ddl);     }            protected void Page_Load(object sender, EventArgs e)    {        //if (!IsPostBack)        //{        //    ShowPage();        //}    }    //public void ShowPage()    //{    //    DropDownList ddl = new DropDownList();    //    ddl.AutoPostBack = true;    //    ddl.Items.Add(new ListItem("国家", "c"));    //    ddl.Items.Add(new ListItem("中國", "c1"));    //    ddl.Items.Add(new ListItem("美國", "c2"));    //    ddl.SelectedIndexChanged += new EventHandler(ddl_SelectedIndexChanged);    //    this.Form.Controls.Add(ddl);    //}    protected void ddl_SelectedIndexChanged(object sender, EventArgs e)    {        DropDownList dl = (DropDownList)sender;        Response.Write("<script>alert(‘" + dl.SelectedValue + "‘)</script>");    }