How to download a webfile in C#

Synchronous File Download

To download a file synchronously, which will block the UI thread, you can use the WebClient.DownloadFile method.

// Web URL of the file to download
string url = "https://www.google.com/images/icons/ui/doodle_plus/logo.png";
// Local file path to save the downloaded file
string localPath = "C:/users/desktop/logo.png";

using (var client = new WebClient())
{
    client.DownloadFile(url, localPath);
}

The above code downloads a file from the provided URL and saves it to the local path. Note that the using statement ensures the WebClient instance is disposed of properly.

You can also download a file and save it with its original name like this:

private void downloadFile()
{
    string desktopPath = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
    string url = "https://www.google.com/images/icons/ui/doodle_plus/logo.png";
    string filename = getFilename(url);

    using (var client = new WebClient())
    {
        client.DownloadFile(url, Path.Combine(desktopPath, filename));
    }

    MessageBox.Show("Download completed");
}

private string getFilename(string url)
{
    Uri uri = new Uri(url);
    return Path.GetFileName(uri.LocalPath);
}

Asynchronous File Download

To prevent freezing the UI, you should download files asynchronously. This is done using the WebClient.DownloadFileAsync method.

For example, How to download a file asynchronously while displaying the download progress:

private void downloadFile()
{
    string desktopPath = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
    string url = "http://feelgrafix.com/data/wallpaper-hd/Wallpaper-HD-11.jpg";
    string filename = getFilename(url);

    using (WebClient wc = new WebClient())
    {
        wc.DownloadProgressChanged += wc_DownloadProgressChanged;
        wc.DownloadFileCompleted += wc_DownloadFileCompleted;
        wc.DownloadFileAsync(new Uri(url), Path.Combine(desktopPath, filename));
    }
}

private void wc_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
{
    progressBar1.Value = e.ProgressPercentage;
}

private void wc_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
{
    progressBar1.Value = 0;

    if (e.Cancelled)
    {
        MessageBox.Show("Download was cancelled");
        return;
    }

    if (e.Error != null)
    {
        MessageBox.Show("An error occurred while downloading the file");
        return;
    }

    MessageBox.Show("File downloaded successfully");
}

Showing Download Progress

You can display download progress in a progress bar. The DownloadProgressChanged event provides information such as the percentage of completion and the number of bytes received.

private void wc_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
{
    Console.WriteLine($"{e.ProgressPercentage}% | {e.BytesReceived} bytes out of {e.TotalBytesToReceive} bytes downloaded.");
}

Cancelling an Asynchronous Download

If you need to cancel an ongoing download, you can do so by calling CancelAsync on the WebClient instance.

private WebClient client;

private void downloadFile()
{
    string url = "https://www.google.com/images/icons/ui/doodle_plus/logo.png";
    string localPath = "C:/users/desktop/logo.png";

    client = new WebClient();
    client.DownloadFileAsync(new Uri(url), localPath);
}

private void cancelDownload()
{
    client.CancelAsync();
}

To track cancellation, add the DownloadFileCompleted event handler to check if the download was cancelled:

private void wc_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
{
    if (e.Cancelled)
    {
        MessageBox.Show("Download cancelled");
    }
}

By using asynchronous methods, you can prevent freezing the UI, and with WebClient's built-in event handlers, you can easily track the download’s progress or cancel it if needed.

Additionally, before starting a download, it’s good practice to check if the device has an active internet connection. You can do this by using NetworkInterface.GetIsNetworkAvailable():

if (System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable())
{
    MessageBox.Show("Internet is available, proceed with the download");
}
else
{
    MessageBox.Show("No internet connection available");
}