动态生成的DropDownList控件，为什么不响应事件？

我想实现：
点击一个按钮，则自动在 TABLE中 加入一行，生成并加入一个 DropDownList 控件

要对 DropDownList 控件的SelectedIndexChanged 事件响应。



我对思归大哥的程序作了如下添加：

int Count
{
get
{
object o = ViewState["Count"];
if(o==null)
return 0;
return (int)ViewState["Count"];
}
set
{
ViewState["Count"] = value;
}
}
DropDownList AddDDL()
{
TableRow tr = new TableRow();
TableCell tc = new TableCell();

DropDownList ddl = new DropDownList();
<<<<<<<以下这三行是我加的
ddl.Items.Add(new ListItem("1","1"));
ddl.Items.Add(new ListItem("2","2"));
ddl.SelectedIndexChanged +=new EventHandler(ddl_SelectedIndexChanged);
tc.Controls.Add(ddl);
tr.Cells.Add(tc);
myTab.Rows.Add(tr);

return ddl;
}

protected void ddl_SelectedIndexChanged(Object o ,EventArgs e)
{
Response.Write("OK");
}

void PopulateDLL(DropDownList ddl)
{
for(int i = 0; i < Count; i++)
{
AddDDL();
}
}

protected void Add(Object sender,EventArgs e)
{
DropDownList ddl = AddDDL();
PopulateDLL(ddl);
Count++;
}


请参考

http://expert.csdn.net/Expert/topic/2229/2229874.xml?temp=.7068903