AsyncTask with update?

Question

Yo, I created a web project to check if it is possible to create asyncTask to update the Progressbar:

public partial class AsyncTest : System.Web.UI.Page
{
    private String _taskprogress;
    private AsyncTaskDelegate _dlgt;
    protected delegate void AsyncTaskDelegate();

    protected void Page_Load(object sender, EventArgs e)
    {
    }

    public String GetAsyncTaskProgress()
    {
        return _taskprogress;
    }

    public IAsyncResult OnBegin(object sender, EventArgs e,
       AsyncCallback cb, object extraData)
    {
        _taskprogress = "AsyncTask started at: " + DateTime.Now + ". ";

        _dlgt = new AsyncTaskDelegate(ReadFile);
        IAsyncResult result = _dlgt.BeginInvoke(cb, extraData);

        return result;
    }

    public void ReadFile()
    {
        try
        {
            string Filename = @"D:\Material.txt";
            int filelength = TotalLines(Filename); //just reads the lines of the file

            ProgressBar1.Maximum = filelength;

            using (StreamReader reader = new StreamReader(Filename))
            {
                string line;
                int actualfileline = 1;
                while ((line = reader.ReadLine()) != null)
                {
                    string test = line;
                    ProgressBar1.Value = actualfileline;
                    actualfileline++;
                    //UpdatePanel1.Update(); <- Doesnt work
                    System.Threading.Thread.Sleep(5);
                }
            }
        }
        catch (Exception ex)
        {
            string exm = ex.Message.ToString();
        }
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        OnBegin(this, null, null, null);

    }
}

Aaaand my aspx code: (I have a script too)

<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
    <ContentTemplate>
        <asp:Button runat="server" ID="btnDoTask" Text="Do Task" OnClick="Button1_Click" />
        <br />
        <br />
        <eo:ProgressBar ID="ProgressBar1" runat="server" Width="250px" 
            BackgroundImage="00060301" BackgroundImageLeft="00060302" 
            BackgroundImageRight="00060303" ControlSkinID="None" IndicatorImage="00060304">
        </eo:ProgressBar
    </ContentTemplate>
</asp:UpdatePanel>

Calling Updatepanel1.Update () does not work because it says:

You can only render rendering-methoe bevor

So how else can I update it? I want the user to see progress in the progress panel - because I want to implement most of the code that reads files. Im really new to asynchronous programming, so I'm not sure if there is anything you need: /

Edit:

Ok, now I created a web service on my page:

[System.Web.Services.WebMethod]
[System.Web.Script.Services.ScriptMethod]
public string GetProcess()
{
    if (actualfileline != null)
    {
        return actualfileline.ToString();
    }
    else
    {
        return "0";
    }
}

And I want to call it through my button:

<asp:Button runat="server" ID="btnDoTask" Text="Do Task" OnClick="Button1_Click" OnClientClick="StartJavaScriptProgress()" />

Javascript part:

function StartJavaScriptProgress()
{
    var elm = document.getElementById("LabelProgress");
    elm.innerText = "Currently Working ...";
    setTimeout(WebService(), 1000);
};

function WebService() {
    $.ajax(
    {
        type: "POST",
        url: "AsyncTest.aspx/GetProcess",
        data: "{}",
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function (response) {
            alert("Worked");
            var elm = document.getElementById("ProgressBar1");
            elm.value = response.d; 
        },
        error: function (jqXHR, textStatus, errorThrown) {

            alert("Error starting process");
        }
    })
};

But it does not work ...

Answer 1

-, . API, ReadLineAsync, HTTP- RegisterAsyncTask, :

// Make sure to enable asynchronous request processing:
// <%@ Page Async="true" ... %>

public partial class AsyncTest : System.Web.UI.Page
{
    private String _taskprogress;

    protected void Page_Load(object sender, EventArgs e)
    {
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        RegisterAsyncTask(new PageAsyncTask(ReadFileAsync));
    }

    public async Task ReadFileAsync()
    {
        try
        {
            string Filename = @"D:\Material.txt";
            int filelength = TotalLines(Filename); //just reads the lines of the file

            ProgressBar1.Maximum = filelength;

            using (StreamReader reader = new StreamReader(Filename))
            {
                string line;
                int actualfileline = 1;
                while ((line = await reader.ReadLineAsync()) != null)
                {
                    string test = line;
                    ProgressBar1.Value = actualfileline;
                    actualfileline++;
                    //UpdatePanel1.Update(); <- Doesnt work
                    System.Threading.Thread.Sleep(5);
                }
            }
        }
        catch (Exception ex)
        {
            string exm = ex.Message.ToString();
        }
    }
}

, .. , HTTP- . . -, - , ReadFileAsync .

, AJAX XHR . XHR . ReadFileAsync , . Session["actualfileline"] = actualfileline. Session["actualfileline"] XHR.