DropDownList获取的SelectIndex一直为0的问题

<asp:DropDownList ID="ddlNameList" runat="Server" Height="30"
AutoPostBack="True" onselectedindexchanged="ddlNameList_SelectedIndexChanged" ></asp:DropDownList>

protected void Page_Load(object sender, EventArgs e)
{

if (!Page.IsCallBack)
{
this.fillIntoNameList();
}
}

protected void Page_Load(object sender, EventArgs e)
{

if (!Page.IsPostBack)
{
this.fillIntoNameList();
}
}