WebClient DownloadFileAsync（）不起作用

Question

WebClient DownloadFileAsync（）不能使用相同的URl和證書...

任何線索？

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

在異步下載完成時需要保持程序運行，因爲它在另一個線程中運行。

嘗試這樣的事情，並等待它說完成您按下Enter鍵結束程序：

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"); 
} 

，取決於您所使用本什麼樣的應用程序，主線程需要保持在後臺線程下載文件時運行。

Answer 2

通過聲明主功能爲async，您還可以使用DownloadFileTaskAsync和await。

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); 
    } 
}