Keep FileUpload control value on PostBack in ASP.Net

File upload inside update panel after postback not showing file.

I have file upload and after that 2 postback.

First is on lnkaddnew at that time i made some calculations on codebehind and on btnsave, i save it all but on click of lnkaddnew FileUpload lost file.

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <ContentTemplate>
        <label for="">Link Expiry</label>
        <asp:TextBox ID="txtLinkExpiryDate" runat="server"></asp:TextBox>
        <asp:FileUpload ID="FileUpload1" CssClass="fileInput" runat="server" />
        <asp:UpdatePanel ID="UpdatePanel3" runat="server">
            <ContentTemplate>
                <div class="addnewo">
                    <asp:LinkButton ID="lnkbtnAddNew" OnClick="lnkbtnAddNew_Click" runat="server">Add New </asp:LinkButton>
                </div>
            </ContentTemplate>
        </asp:UpdatePanel>
        <asp:Button ID="btnSave" runat="server" Text="Save" OnClick="btnSave_Click" />
    </ContentTemplate>
    <Triggers>
        <asp:PostBackTrigger ControlID="btnSave" />
    </Triggers>
</asp:UpdatePanel>

ON Page Load i added

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