如何把一个表的数据绑定到asp组件dropdownlist中？(50分)

如题。

eg:
protected DropDownList ddlTest;
.....
DataTable dtSell;
ddlTest.DataSource = dtSell;
ddlTest.DataValueField = "ID";
ddlTest.DataValueField = "Name";
ddlTest.DataBind();
PS:
SetValue Example: ddlTest.SelectedIndex = ddlTest.Items.IndexOf(ddlTest.Items.FindByValue("12"));
GetValue Example: int ID = int.Parse(ddlTest.SelectItem.Value);

为什么写两个？
ddlTest.DataValueField = "ID";
ddlTest.DataValueField = "Name";

ddlTest.DataTextField = "ID";
ddlTest.DataValueField = "Name";

一个为显示，一个为取值。