SharePoint : FileUpload control hasfile propertie always false

I used FileUpload control on my SharePoint UserControl. Even after choosing a file,it shows FileUpload Control's "hasfile" property as false.

<asp:UpdatePanel ID="UPanProcesses" runat="server">

<ContentTemplate>

<asp:FileUpload ID='FileUploadPhoto' runat="server" />

<asp:Button ID="ButtonSave" runat="server" Text="Enregistrer" OnClick="ButtonSave_Click" ></asp:Button>

</ContentTemplate>

</asp:UpdatePanel>

Code Behind :

protected void  ButtonSave _Click(object sender, EventArgs e)

{

  if (FileUploadPhoto.HasFile)

    {    

             byte[] data = FileUploadPhoto.FileBytes;

              item.Attachments.Add(FileUploadPhoto.FileName, data);

     }

}

The solution :

Add a trigger for your UpdatePanel
    <Triggers>

        <asp:PostBackTrigger ControlID="ButtonSave" />

    </Triggers>

This will force a postback when the upload button is clicked.

Also add the line below to the Page_Load
Page.Form.Attributes.Add("enctype", "multipart/form-data");

</ContentTemplate>

    <Triggers>

        <asp:PostBackTrigger ControlID=" ButtonSave " />

    </Triggers>

</asp:UpdatePanel>

protected void Page_Load(object sender, EventArgs e)

{

     Page.Form.Attributes.Add("enctype", "multipart/form-data");

}