Styjun

I have an app written in C#. In this app, I need to download multiple files. Once all of the files are downloaded, I need to do something else. In an effort to download the files at the same time, I've written the following:

private void DownloadFiles(string[] targets)

 var tasks = new List<Task>();
 foreach (var target in targets)
 
 var task = DownloadFile(target);
 tasks.Add(task);
 

 Task.WaitAll(tasks.ToArray());


private async Task DownloadFile(string target)

 using (var wc = new WebClient())
 
 wc.DownloadProgressChanged += (object sender, DownloadProgressChangedEventArgs e) => 
 Console.WriteLine(e.ProgressPercentage + "% downloaded.");
 

 wc.DownloadFileCompleted += (object sender, AsyncCompletedEventArgs e) => 
 Console.WriteLine(target + " was downloaded.");

 // TODO: Signal this "Task" is done
 

 await wc.DownloadFileTaskAsync(target, localPath);
 

Maybe I'm confused. In my opinion, I think I need to do something in DownloadFileCompleted. Or, maybe the await wc.DownloadFileTaskAsync line is sufficient.

How do I download multiple files at the same time, but wait until they're all download before continuing?

You could do the following:

private void DownloadFiles(string[] targets)

 var tasks = new List<Task>();
 using (var wc = new WebClient())
 
 foreach (var target in targets)
 
 var task = DownloadFile(wc, target);
 tasks.Add(task);
 
 Task.WaitAll(tasks.ToArray());
 



private Task DownloadFile(WebClient wc, string target)
 
 wc.DownloadProgressChanged += (object sender, DownloadProgressChangedEventArgs e) =>
 
 Console.WriteLine(e.ProgressPercentage + "% downloaded.");
 ;

 wc.DownloadFileCompleted += (object sender, AsyncCompletedEventArgs e) =>
 
 Console.WriteLine(target + " was downloaded.");
 // TODO: Signal this "Task" is done
 ;

 return wc.DownloadFileTaskAsync(target, localPath);
 

I moved the WebClient to the calling method because you will have to keep it open until all downloads finished (which you don't know when they will within your DownloadFile method).

Additionally I removed the async from your method declaration because you don't have to wait for something within the method.