I'd like to know if there is a way in ASP.NET C# to somehow show to the user that the work is still going while executing something that take ages to end.

Let me explain a bit more with some code. First I have a ASPX page that show some fileUpload items and a button to send the form to the server. It allows the user to send 3 differents file that are each processed differently :

<%@ Page Title="" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeBehind="MassUpdates.aspx.cs" Inherits="MassUpdates" %>
<asp:Content ID="Content1" ContentPlaceHolderID="MainContent" runat="server">
    <h3 style="font: bold;">Mass Updates</h3>
    <hr />
    <div class="row">
        <div class="col-12 mb-2">
            <asp:Label ID="Label0" runat="server" Text="File 1 : "></asp:Label>
            <asp:FileUpload ID="fup1" runat="server" />
        </div>
        <div class="col-12 mt-2 mb-2">
            <asp:Label ID="Label1" runat="server" Text="File 2 : "></asp:Label>
            <asp:FileUpload ID="fup2" runat="server" />
        </div>
        <div class="col-12 mt-2 mb-2">
            <asp:Label ID="Label2" runat="server" Text="File 3 : "></asp:Label>
            <asp:FileUpload ID="fup3" runat="server" />
        </div>
    </div>
    <div class="row">
        <div class="col-12 mt-2">
            <asp:Button ID="btnEnvoi" runat="server" Text="Envoyer" OnClick="btnEnvoi_Click" />
        </div>
        <div class="col-12 mt-2">
            <asp:Label ID="lblMsg" runat="server" Text="" Visible="false"></asp:Label>
        </div>
    </div>
</asp:Content>

Then, on the code behind page, I have a tiny function called when the user press the button that call every file process if the file has been dropped :

protected void btnSend_Click(object sender, EventArgs e)
{
    if (fup1.HasFiles)
    {
        result += trtFile1(); // Return a string that give the final feedback of the execution for File 1
    }

    if (fup2.HasFiles)
    {
        result += trtFile2(); // Return a string that give the final feedback of the execution for File 2
    }

    if (fup3.HasFiles)
    {
        result += trtFile3(); // Return a string that give the final feedback of the execution for File 3
    }

    lblMsg.Text = result;
}

But as I said earlier, if the user sends 3 huge files, doing all the process take years (it's a picture) and they wonder if the application as crashed or is still running.

What I want to know, is if there is a way to send to the client side page some informations (like a text or a value to set in a progress bar) when we reached a step on the function. Something like that :

protected void btnSend_Click(object sender, EventArgs e)
{
    if (fup1.HasFiles)
    {
        // Send to the client that we start file 1
        result += trtFile1(); // Return a string that give the final feedback of the execution for File 1
    }

    if (fup2.HasFiles)
    {
        // Send to the client that we start file 2
        result += trtFile2(); // Return a string that give the final feedback of the execution for File 2
    }

    if (fup3.HasFiles)
    {
        // Send to the client that we start file 3
        result += trtFile3(); // Return a string that give the final feedback of the execution for File 3
    }

    lblMsg.Text = result;
}

Thanks if anyone of you already heard about this kind of functionality or has something similar in his pocket !

Rolstyam.