WebClient DownloadFileAsync()不起作用

Question

WebClient DownloadFileAsync()不能使用相同的URl和凭据...

有什么线索吗？

 static void Main(string[] args)
        {
            try
            {
                var urlAddress = "http://mywebsite.com/msexceldoc.xlsx";


                using (var client = new WebClient())
                {
                    client.Credentials = new NetworkCredential("UserName", "Password");
                    // It works fine.  
                    client.DownloadFile(urlAddress, @"D:\1.xlsx");
                }

                /*using (var client = new WebClient())
                {
                   client.Credentials = new NetworkCredential("UserName", "Password");

                    // It y creats file with 0 bytes. Dunow why is it. 
                    client.DownloadFileAsync(new Uri(urlAddress), @"D:\1.xlsx");
                    //client.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);

                }*/
            }
            catch (Exception ex)
            {

            }
        }

Answer 1

您需要在异步下载完成时保持程序运行，因为它在另一个线程中运行。

尝试类似这样的操作，并等待它显示已完成，然后按enter键结束程序：

static void Main(string[] args)
    {
        try
        {
            var urlAddress = "http://mywebsite.com/msexceldoc.xlsx";

            using (var client = new WebClient())
            {
               client.Credentials = new NetworkCredential("UserName", "Password");

                client.DownloadFileAsync(new Uri(urlAddress), @"D:\1.xlsx");
                client.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
        }
        catch (Exception ex)
        {

        }

    Console.ReadLine();
    }

public static void Completed(object o, AsyncCompletedEventArgs args)
{
    Console.WriteLine("Completed");
}

主线程需要在后台线程下载文件时保持运行，这取决于你在哪种类型的应用中使用它。

Answer 2

通过将Main函数声明为async，您还可以将DownloadFileTaskAsync与await一起使用。

public static async void Main(string[] args)
{
    var urlAddress = "http://mywebsite.com/msexceldoc.xlsx";
    var fileName = @"D:\1.xlsx";

    using (var client = new WebClient())
    {
        await client.DownloadFileTaskAsync(new Uri(urlAddress), fileName);
    }
}