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适当的信息,这样UI就不会冻结.

这是代码:

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.我如何使用内置函数来下载站点的字节(以后使用我将它转换为字符串,我知道如何做到这一点)并且不冻结我的GUI？

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

谢谢你,你总是这么好的资源.

Answer 1

你需要处理这个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,您将进入DownloadDataCompleted另一个线程; 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,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);
}