Question

我的计划是让用户在我的程序中写下一个电影标题，我的程序将异步提取适当的信息，这样UI就不会冻结。

以下是代码：

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。我不能使用字符串URL。如何使用内置函数下载站点的字节（以后使用我会将其转换为字符串，我知道如何执行此操作）并且不会冻结我的GUI？

也许是DownloadDataAsync的明确示例，以便我可以学习如何使用它？

非常感谢，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");
}

args包含与错误条件等相关的其他信息 - 请检查这些信息。

另请注意，您将在另一个主题上进入DownloadDataCompleted;如果您在UI（winform，wpf等）中，则需要在更新UI之前进入UI线程。从winforms中，使用this.Invoke。对于WPF，请查看Dispatcher。

Answer 2

有一个较新的DownloadDataTaskAsync方法，允许您等待结果。阅读起来更简单，更容易接线。我会用那个......

var client = new WebClient();

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

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

Answer 3

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 4

如果在网络应用程序或网站上使用上述任何人，请在aspx文件的页面指令声明中设置Async =“true”。

Answer 5

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

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

Answer 6

//使用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);
}

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

6 个答案: