Don't Work FileUpload in UpdatePanel

Question

<asp:ScriptManager runat="server" ID="S"></asp:ScriptManager>
<asp:UpdatePanel runat="server" ID="U" UpdateMode="Conditional">
    <ContentTemplate>
        <asp:Panel runat="server" ID="U1">
            <asp:Button runat="server" ID="Btnnew" Text="new" OnClick="Btnnew_Click"/>
        </asp:Panel>
        <asp:Panel runat="server" ID="U2">
            <asp:FileUpload runat="server" ID="FU" />
            <asp:Button  runat="server" ID="Btnok" OnClick="Btnok_Click"  Text="ok"/>
        </asp:Panel>
    </ContentTemplate>
    <Triggers>
        <asp:PostBackTrigger ControlID="btnok" />
    </Triggers>
</asp:UpdatePanel>

and server code is

protected void Page_Load(object sender, EventArgs e)
{
    U1.Visible = true;
    U2.Visible = false;
    U.Update();
}
protected void Btnnew_Click(object sender, EventArgs e)
{
    U1.Visible = false;
    U2.Visible = true;
    U.Update();
}
protected void Btnok_Click(object sender, EventArgs e)
{
    U.Update();
    FU.PostedFile.SaveAs("");
}

but File upload is Null. Nobody can help me!!!

Answer 1

Unfortunately you can't use another container inside UpdatePanel to hold the FileUpload control. But you can do like this:

In the markup:

<asp:ScriptManager runat="server" ID="S"></asp:ScriptManager>
<asp:UpdatePanel runat="server" ID="U" UpdateMode="Conditional">
    <ContentTemplate>
            <asp:Button runat="server" ID="Btnnew" Text="new" OnClick="Btnnew_Click" />
            <asp:FileUpload runat="server" ID="FU" />
            <asp:Button runat="server" ID="Btnok" OnClick="Btnok_Click" Text="ok" />
    </ContentTemplate>
    <Triggers>
        <asp:PostBackTrigger ControlID="Btnok" />
    </Triggers>
</asp:UpdatePanel>

And change your code to hide/unhide the contols, and to save the file:

protected void Page_Load(object sender, EventArgs e)
{
    Btnnew.Visible = true;
    FU.Visible = false;
    Btnok.Visible = false;
    U.Update();
}
protected void Btnnew_Click(object sender, EventArgs e)
{
    Btnnew.Visible = false;
    FU.Visible = true;
    Btnok.Visible = true;
    U.Update();
}
protected void Btnok_Click(object sender, EventArgs e)
{
    if (FU.HasFile)
    {
        string fileName = FU.FileName;
        FU.SaveAs(Server.MapPath("~/Images/") + fileName);// Assuming you have Images folder in the root
    }
    U.Update();
}

You can use <div> or <table> and with css make them look like a panel if you wish.