Question

I´m currently trying to add parallel downloads to my application but I don´t know how to handle the DownloadProgressChangedEvent to display the progress in multiple progressbars.

I´m using a datagridview with predefined rows for each file the user is able to download and each row has a cell with a progressbar in it.

The problem now is, that I don´t know how to update each progressbar individually, because right now, all selected progressbars are showing the same percentage and they´re just jumping between the progress of download1 & download2.

Here´s the code im using:

To start the downloads:

private void download_button_Click(object sender, EventArgs e)
    {
        start = DateTime.Now;
        download_button.Enabled = false;

        Rows = dataGridView1.Rows.Count;
        Checked = 0;

        CheckedCount = 0;

            //count the selected rows
            for (i = 0; i < Rows; i++)
            {
                Checked = Convert.ToInt32(dataGridView1.Rows[i].Cells["checkboxcol"].FormattedValue);

                CheckedCount += Checked;

                richTextBox3.Text = CheckedCount.ToString();
            }


        for (int z = 1; z < CheckedCount; z++)
        {             
            _MultipleWebClients = new WebClient();

            _MultipleWebClients.DownloadFileCompleted += new AsyncCompletedEventHandler(_DownloadFileCompleted);
            _MultipleWebClients.DownloadProgressChanged += new System.Net.DownloadProgressChangedEventHandler(_DownloadProgressChanged);
            _MultipleWebClients.DownloadFileAsync(new Uri(_downloadUrlList[z].ToString()), @"F:\test" + z + ".mp4");     
        }

    }

(I´m also unable to download more than two files simultaneously – the third download won´t start until the first two are finished)

---

DownloadProgressChangedEvent:

    private void _DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
    {
        progressBar1.Value = e.ProgressPercentage;
        for (int c = 0; c < CheckedCount; c++)
        {
            dataGridView1.Rows[_downloadRowNrList[c]].Cells[3].Value = e.ProgressPercentage;
        }

        float size = ((e.TotalBytesToReceive / 1024) / 1024);
        label1.Text = size.ToString();

        double dn = (double)e.BytesReceived / 1024.0 / (DateTime.Now - start).TotalSeconds;
        label2.Text = (dn.ToString("n") + " KB/s) " + e.ProgressPercentage);        
    }

The problem probably is, that all progressbars are using the same DownloadProgressChangedEvent, but I´m not sure how to create multiple of these events without knowing the needed number…

So i hope that someone is able to help me with this,

thanks in advance!

Answer 1

What you want to do is use the other DownloadFileAsync method:
http://msdn.microsoft.com/en-us/library/ms144197.aspx

The third parameter is a userToken which gets passed as part of the DownloadProgressChangedEventArgs (it’s in the UserState property).

So, when you make the DownloadFileAsync call, pass in a unique token (an integer, or something else) that you can then associate with the progressBar that needs updating.

    //(Snip)

    //in download_button_Click, pass the row you are updating to the event.
    for (int z = 1; z < CheckedCount; z++)
    {             
        _MultipleWebClients = new WebClient();

        _MultipleWebClients.DownloadFileCompleted += new AsyncCompletedEventHandler(_DownloadFileCompleted);
        _MultipleWebClients.DownloadProgressChanged += new System.Net.DownloadProgressChangedEventHandler(_DownloadProgressChanged);
        _MultipleWebClients.DownloadFileAsync(new Uri(_downloadUrlList[z].ToString()), @"F:\test" + z + ".mp4", dataGridView1.Rows[z]);     
    }
}

private void _DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
{
    var rowToUpdate = (DataGridViewRow)e.UserState;
    RowToUpdate["ProgressBar"].Value = e.ProgressPercentage;
    RowToUpdate["TextProgress"].Value = e.ProgressPercentage;
    RowToUpdate["BytesToRecive"].Value = ((e.TotalBytesToReceive / 1024) / 1024).ToString();

    double dn = (double)e.BytesReceived / 1024.0 / (DateTime.Now - start).TotalSeconds;
    RowToUpdate["Speed"].Value = (dn.ToString("n") + " KB/s) " + e.ProgressPercentage);
}