为什么CheckBoxList 绑定数据后 要在读取不到Text 和Value ？

...
CheckBoxList.DataSource = dt;
CheckBoxList.DataTextField = "text"; CheckBoxList.DataValueField = "id";
CheckBoxList.DataBind();

for (int i = 0; i < ChenkBoxList.Items.Count; i++)
{
if (ChenkBoxList.Items[i].Selected == true)
{
Label1.Text += ChenkBoxList.Items[i].Value + "|";
}
}

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
...
CheckBoxlist.DataSource = dt;
CheckBoxlist.DataTextField = "Text";
CheckBoxlist.DataValueField = "id";
CheckBoxlist.DataBind();

...
}
}