How to Download Files With C# from a Web Server

How to use C# to manage Internet communications and download files with C# or collect information and data from web services.

There are two methods for downloading a file with C#, synchronously and asynchronously.

Synchronous requests execute sequentially, blocking further code execution until the request is completed, which can lead to slower performance. Asynchronous requests allow code to continue executing while waiting for a response, improving overall responsiveness and efficiency, especially in web applications. Asynchronous programming is often preferred for tasks like fetching data from servers or performing I/O operations, where waiting for a response should not hinder other processes.

Synchronous Download Files With C#

A Synchronous download will only allow one download to be processed. While it is being processed, the main program thread will pause until the download is complete. It is the simplest method to implement, and if you can wait for the download to complete, it is often the best.

using System.Net;

using(WebClient fileDownloader = new WebClient())
{
  fileDownloader.DownloadFile("https://lonewolfonline.net/robots.txt", "c:\robots.txt");
}

Asynchronous Download Files With C#

An asynchronous download does not block the main program thread apart from the initial DNS lookup (converting a hostname to an IP address). Using an IP address directly can avoid this delay. This method is more involved, but if you cannot wait for the download to finish or need to download a large file, this is the best method.

using System.Net;

using(WebClient fileDownloader = new WebClient())
{
  fileDownloader.DownloadFileAsync("https://lonewolfonline.net/robots.txt", "c:\robots.txt");
}

The Asynchronous Download method also contains a few events that can be used for progress bars and notifications, as well as an event that is triggered on completion of the download.

...
fileDownloader.DownloadProgressChanged += new DownloadProgressChangedEventHandler(updateProgress);
...

private void updateProgress(object sender, DownloadProgressChangedEventArgs Arg)
{
  progressBar.Value = Arg.ProgressPercentage;
}