Question

我的应用程序从各种网址下载数据。每次URL下载完成时我都想知道 - 成功还是失败。为此，我有以下代码。

static void Main(string[] args)
{
    var URLsToProcess = new List<string>
        {
             "http://www.microsoft.com",
             "http://www.stackoverflow.com",
             "http://www.google.com",
             "http://www.apple.com",
             "http://www.ebay.com",
             "http://www.oracle.com",
             "http://www.gmail.com",
             "http://www.amazon.com",
             "http://www.outlook.com",
             "http://www.yahoo.com",
             "http://www.amazon124.com",
             "http://www.msn.com"
         };


     var tasks = URLsToProcess.Select(uri => DownloadStringAsTask(new Uri(uri))).ToArray();

     while (tasks.Any())
     {
         try
         {
             //Task.WaitAll(tasks);
             int index = Task.WaitAny(tasks);
             Console.WriteLine("{0} has completed", tasks[index].AsyncState.ToString());
             tasks = tasks.Where(t => t != tasks[index]).ToArray();
             break;
         }
         catch (Exception e)
         {
             foreach (var t in tasks.Where(t => t.Status == TaskStatus.Faulted))
                 Console.WriteLine("{0} has failed", t.AsyncState.ToString());
             // handle exception/report progress...
             tasks = tasks.Where(t => t.Status != TaskStatus.Faulted).ToArray();
         }
     }   
 }

 static Task<string> DownloadStringAsTask(Uri address)
 {
     TaskCompletionSource<string> tcs = new TaskCompletionSource<string>(address);
     WebClient client = new WebClient();
     client.DownloadStringCompleted += (sender, args) =>
     {
         if (args.Error != null)
             tcs.SetException(args.Error);
         else if (args.Cancelled)
             tcs.SetCanceled();
         else
             tcs.SetResult(args.Result);
     };
     client.DownloadStringAsync(address);
     return tcs.Task;
 }

但是我只在输出中获得一个URL。知道我在这里做错了吗？

Answer 1

您的break循环中有一个无关的while：

while (tasks.Any())
{
    try
    {
        //Task.WaitAll(tasks);
        int index = Task.WaitAny(tasks);
        Console.WriteLine("{0} has completed", tasks[index].AsyncState.ToString());
        tasks = tasks.Where(t => t != tasks[index]).ToArray();
        //break;  // NOTE: extraneous break that I have commented out
    }

使用break ，，您的代码在我的机器上产生以下输出：

http://www.microsoft.com/ has completed

如上所示，break 已注释，您的代码在我的机器上产生了以下输出：

http://www.microsoft.com/ has completed
http://www.apple.com/ has completed
http://www.oracle.com/ has completed
http://www.amazon124.com/ has completed
http://www.google.com/ has completed
http://www.msn.com/ has completed
http://www.stackoverflow.com/ has completed
http://www.amazon.com/ has completed
http://www.ebay.com/ has completed
http://www.gmail.com/ has completed
http://www.outlook.com/ has completed
http://www.yahoo.com/ has completed

每次任务完成时都尝试获取更新

1 个答案: