等待 WebClient.DownloadFileTaskAsync 不起作用

Question

I'm trying to use WebClient.DownloadFileTaskAsync to download a file so that I can make use of the download progress event handlers. The problem is that even though I'm using await on DownloadFileTaskAsync , it's not actually waiting for the task to finish and exits instantly with a 0 byte file. What am I doing wrong?

internal static class Program
{
    private static void Main()
    {
        Download("http://ovh.net/files/1Gb.dat", "test.out");
    }

    private async static void Download(string url, string filePath)
    {
        using (var webClient = new WebClient())
        {
            IWebProxy webProxy = WebRequest.DefaultWebProxy;
            webProxy.Credentials = CredentialCache.DefaultCredentials;
            webClient.Proxy = webProxy;
            webClient.DownloadProgressChanged += (s, e) => Console.Write($"{e.ProgressPercentage}%");
            webClient.DownloadFileCompleted += (s, e) => Console.WriteLine();
            await webClient.DownloadFileTaskAsync(new Uri(url), filePath).ConfigureAwait(false);
        }
    }
}

Answer 1

As others have pointed, The two methods shown are either not asynchronous or not awaitable.

First, you need to make your download method awaitable:

private async static Task DownloadAsync(string url, string filePath)
{
    using (var webClient = new WebClient())
    {
        IWebProxy webProxy = WebRequest.DefaultWebProxy;
        webProxy.Credentials = CredentialCache.DefaultCredentials;
        webClient.Proxy = webProxy;
        webClient.DownloadProgressChanged += (s, e) => Console.Write($"{e.ProgressPercentage}%");
        webClient.DownloadFileCompleted += (s, e) => Console.WriteLine();
        await webClient.DownloadFileTaskAsync(new Uri(url), filePath).ConfigureAwait(false);
    }
}

Then, you either wait on Main :

private static void Main()
{
    DownloadAsync("http://ovh.net/files/1Gb.dat", "test.out").Wait();
}

Or, make it asynchronous , too:

private static async Task Main()
{
    await DownloadAsync("http://ovh.net/files/1Gb.dat", "test.out");
}