等待每个人-如何等待每个迭代完成？

Question

I have a list of URL's List<string> . I want to loop through each URL and download the content on the page. The method that downloads the content from a URL is asynchronous. I want to wait for each iteration to complete

foreach(string url in urlList)
{
    await DownloadPage(url);
}

Download Method:

private async Task DownloadPage(string url)
{
    // await Download content using HttpClient
    // Save file
}

What's happening at the moment is it's looping through each ForEach without waiting for it to complete.

How can I achieve a solution so that it waits on each iteration for the page to download?

Answer 1

instead of using the await keyword here, you could also call .Result on the method call and the task will be sure to be resolved and you will get the result from it right there on the spot. your code would look like so:

foreach(string url in urlList)
{
    DownloadPage(url).Result;
}

Answer 2

It sounds like you need the Task.WaitAll() method:

// off the top of my head, syntax not guaranteed to be 100% correct :)
List<Task> tasks = new List<Task>();
foreach(string url in urlList) 
{
    tasks.Add(Task.Factory.StartNew(DownloadPage));
    Task.WaitAll(tasks.ToArray()); 
}