[Solved] Maintain state of FileUpload control and preserve file across PostBack in ASP.Net

With Update panel it will not be possible to get the Maintain the FileUpload control.

Without using Update Panel.

HTML

<input id="FileUpload1" name="FileUpload1" type="file" />
<br />
<asp:Label ID="ImageErrorLabel" runat="server" />
<asp:Button ID="Button1" Text="Upload" OnClick="Upload" runat="server" />
<asp:DropDownList ID="ddlTexts" runat="server" AutoPostBack="true" OnSelectedIndexChanged="OnSelectedIndexChanged">
    <asp:ListItem Text="text1" />
    <asp:ListItem Text="text2" />
    <asp:ListItem Text="text2" />
</asp:DropDownList>

Namespace

using System.IO;

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (this.IsPostBack)
    {
        if (Session["FileUpload1"] == null && Request.Files["FileUpload1"].ContentLength > 0)
        {
            Session["FileUpload1"] = Request.Files["FileUpload1"];
            ImageErrorLabel.Text = Path.GetFileName(Request.Files["FileUpload1"].FileName);
            HttpPostedFile file = (HttpPostedFile)Session["FileUpload1"];

        }

        else if (Session["FileUpload1"] != null && (Request.Files["FileUpload1"].ContentLength == 0))
        {
            HttpPostedFile file = (HttpPostedFile)Session["FileUpload1"];
            ImageErrorLabel.Text = Path.GetFileName(file.FileName);

        }

        else if (Request.Files["FileUpload1"].ContentLength > 0)
        {
            Session["FileUpload1"] = Request.Files["FileUpload1"];
            ImageErrorLabel.Text = Path.GetFileName(Request.Files["FileUpload1"].FileName);

        }
    }
}

protected void OnSelectedIndexChanged(object sender, EventArgs e)
{
    HttpPostedFile FileUpload1 = Request.Files["FileUpload1"];

    Session["FileUpload1"] = FileUpload1;
}

protected void Upload(object sender, EventArgs e)
{
    if (Session["FileUpload1"] == null && Request.Files["FileUpload1"].ContentLength > 0)
    {
        Session["FileUpload1"] = Request.Files["FileUpload1"];
        ImageErrorLabel.Text = Path.GetFileName(Request.Files["FileUpload1"].FileName);
        HttpPostedFile file = (HttpPostedFile)Session["FileUpload1"];
        SaveFile(file);
    }

    else if (Session["FileUpload1"] != null && (Request.Files["FileUpload1"].ContentLength == 0))
    {
        HttpPostedFile file = (HttpPostedFile)Session["FileUpload1"];
        ImageErrorLabel.Text = Path.GetFileName(file.FileName);
        SaveFile(file);
    }

    else if (Request.Files["FileUpload1"].ContentLength > 0)
    {
        Session["FileUpload1"] = Request.Files["FileUpload1"];
        ImageErrorLabel.Text = Path.GetFileName(Request.Files["FileUpload1"].FileName);
        SaveFile(Request.Files["FileUpload1"]);
    }
}

private void SaveFile(HttpPostedFile file)
{
    string fname = Path.GetFileName(file.FileName);

    file.SaveAs(Server.MapPath("~/images/" + fname));
    ImageErrorLabel.Text = string.Empty;
}