FileUpload not working in Multiview and updatepanel

<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:UpdatePanel runat="server">
<Triggers>
<asp:PostBackTrigger ControlID="Button1" />
</Triggers>
    <ContentTemplate>

<asp:MultiView ID="MultiView1" runat="server" 
                 ActiveViewIndex="0">           
    <asp:View ID="View1" runat="server">
        <asp:Button Text="next"
            runat="server" onclick="Unnamed1_Click" />
    </asp:View>
    <asp:View ID="View2" runat="server">
    <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" 
        style="width: 56px" />
    <asp:FileUpload ID="fileupload2" runat="server" />
    </asp:View>
</asp:MultiView>
 </ContentTemplate>
</asp:UpdatePanel>

and the code behind is

 protected void Button1_Click(object sender, EventArgs e)
    {
        if (fileupload2.HasFile)
        {
            //code..
        }
    }
    protected void Unnamed1_Click(object sender, EventArgs e)
    {
        MultiView1.ActiveViewIndex = 1;
    }

When i click Button1 for uploading the image on first time the fileupload2.HasFile returns "false"

without refrshing the page again try to upload the same picture then fileupload2.HasFile returns "true"

Working Properly in View1. Problem is with View 2

What is the problem with that fileupload ?

Solution

Try registering the button control with RegisterPostBackControl early in the page lifecycle:

   protected void Page_Init(object sender, EventArgs e)
   {
       ScriptManager1.RegisterPostBackControl(Button1);
   }