FileUpload控件选择完成后执行事件

<asp:FileUpload ID="FileUpload_album" runat="server"   onchange="SelectImg(this)" />

//添加一个隐藏按钮
<span style="display: none"><asp:Button ID="Button_thumb"  runat="server" Text="获取缩略图" OnClick="Button_thumb_Click" /></span>

    <script type="text/javascript">
        function SelectImg() {
            window.document.getElementById('<%=Button_thumb.ClientID %>').click();
            alert(a);
        }
    </script>

C#自由发挥吧