AutoPostBack 与UpdatePanel的局部刷新

前台代码：

<form id="form1" runat="server">
    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <div><asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" 
                onselectedindexchanged="DropDownList1_SelectedIndexChanged">
                <asp:ListItem>新浪</asp:ListItem>
                <asp:ListItem>百度</asp:ListItem>
                <asp:ListItem>谷歌</asp:ListItem>
            </asp:DropDownList>
        <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
        <ContentTemplate>
            <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        </ContentTemplate>
        <Triggers>
        <asp:AsyncPostBackTrigger ControlID="DropDownList1" />
        </Triggers>
        </asp:UpdatePanel>
    </div>
    </form>

后台代码：

 protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
        {
            TextBox1.Text = DropDownList1.SelectedValue;
        }