File Upload Not Function in Update Panel

In Update Panel the file upload doesn't function. When you click the button inside update panel. There are get nothing inside the file. This is because the Update Panel have block the asynchronous postback. You should set the PostBackTrigger for the Update Panel.

<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="conditional">
<Triggers>
<asp:PostBackTrigger ControlID="Button1" />
</Triggers>
<ContentTemplate> 
<asp:FileUpload ID="FileUpload1" runat="server" />
<asp:Button ID="Button1" runat="server" Text="Upload" OnClick="Button1_Click" />
</ContentTemplate>
</asp:UpdatePanel>