如何在此上下文中使用WebClient.DownloadDataAsync（）方法？

Question

我的计划是让用户在我的程序中写下电影标题，我的程序将异步提取相应的信息，以便UI不会冻结。

下面的代码：

public class IMDB 
    { 
     WebClient WebClientX = new WebClient(); 
     byte[] Buffer = null; 


     public string[] SearchForMovie(string SearchParameter) 
     { 
      //Format the search parameter so it forms a valid IMDB *SEARCH* url. 
      //From within the search website we're going to pull the actual movie 
      //link. 
      string sitesearchURL = FindURL(SearchParameter); 

      //Have a method download asynchronously the ENTIRE source code of the 
      //IMDB *search* website. 
      Buffer = WebClientX.DownloadDataAsync(sitesearchURL); 


      //Pass the IMDB source code to method findInformation(). 

      //string [] lol = findInformation(); 

      //???? 

      //Profit. 

      string[] lol = null; 
      return lol; 
     } 

我的实际问题在于WebClientX.DownloadDataAsync（）方法。我无法为它使用字符串网址。我如何使用内置函数来下载网站的字节（以备后用，我将它转换为字符串，我知道如何做到这一点），而不会冻结我的GUI？

也许是DownloadDataAsync的一个明确的例子，所以我可以学习如何使用它？

谢谢，所以你总是这么好的资源。

Answer 1

您需要处理DownloadDataCompleted事件：

static void Main() 
{ 
    string url = "http://google.com"; 
    WebClient client = new WebClient(); 
    client.DownloadDataCompleted += DownloadDataCompleted; 
    client.DownloadDataAsync(new Uri(url)); 
    Console.ReadLine(); 
} 

static void DownloadDataCompleted(object sender, 
    DownloadDataCompletedEventArgs e) 
{ 
    byte[] raw = e.Result; 
    Console.WriteLine(raw.Length + " bytes received"); 
} 

的ARGS包含有关错误条件等信息，其他位 - 检查这些了。

另请注意，您将在不同的线程上进入DownloadDataCompleted;如果您处于UI（winform，wpf等）中，则需要在更新UI之前进入UI线程。从winforms，使用this.Invoke。对于WPF，请看Dispatcher。

Answer 2

static void Main(string[] args) 
{ 
    byte[] data = null; 
    WebClient client = new WebClient(); 
    client.DownloadDataCompleted += 
     delegate(object sender, DownloadDataCompletedEventArgs e) 
     { 
      data = e.Result; 
     }; 
    Console.WriteLine("starting..."); 
    client.DownloadDataAsync(new Uri("http://stackoverflow.com/questions/")); 
    while (client.IsBusy) 
    { 
     Console.WriteLine("\twaiting..."); 
     Thread.Sleep(100); 
    } 
    Console.WriteLine("done. {0} bytes received;", data.Length); 
} 

Answer 3

如果在Web应用程序或网站上面使用人在aspx文件的页指令申报请设置异步=“真”。

Answer 4

有一个较新的DownloadDataTaskAsync方法，允许您等待结果。阅读起来更简单，并且更容易连线。我使用...

var client = new WebClient(); 

var data = await client.DownloadDataTaskAsync(new Uri(imageUrl)); 

await outstream.WriteAsync(data, 0, data.Length); 

Answer 5

//使用的ManualResetEvent类

static ManualResetEvent evnts = new ManualResetEvent(false); 
static void Main(string[] args) 
{ 
    byte[] data = null; 
    WebClient client = new WebClient(); 
    client.DownloadDataCompleted += 
     delegate(object sender, DownloadDataCompletedEventArgs e) 
     { 
      data = e.Result; 
      evnts.Set(); 
     }; 
    Console.WriteLine("starting..."); 
    evnts.Reset(); 
    client.DownloadDataAsync(new Uri("http://stackoverflow.com/questions/")); 
    evnts.WaitOne(); // wait to download complete 

    Console.WriteLine("done. {0} bytes received;", data.Length); 
} 

Answer 6

ThreadPool.QueueUserWorkItem(state => WebClientX.DownloadDataAsync(sitesearchURL)); 

http://workblog.pilin.name/2009/02/system.html