WebClient.DownloadDataAsync() 出现问题。不下载数据？

Question

public string[] SearchForMovie(string SearchParameter) {
WebClientX.DownloadDataCompleted += new DownloadDataCompletedEventHandler(WebClientX_DownloadDataCompleted); WebClientX.DownloadDataAsync（新的 Uri（ "http://www.imdb.com/find?s=all&q=ironman+&x=0&y=0"));

    string sitesearchSource = Encoding.ASCII.GetString(Buffer);
}

void WebClientX_DownloadDataCompleted(object sender,
    DownloadDataCompletedEventArgs e)
{
    Buffer = e.Result;
    throw new NotImplementedException();
}

我得到了这个例外：

矩阵不能为空。引用我的byte[]变量Buffer。

因此，我可以得出结论，DownloadDataAsync 并没有真正下载任何内容。是什么导致了这个问题？

附言。如何轻松格式化我的代码，使其在此处正确缩进。为什么我不能从 Visual C# express 复制过去的代码并在此处保持缩进？谢谢！ :D

Answer 1

这里的关键词是“异步”；当您调用DownloadDataAsync 时，它只会开始 下载；它还没有完成。您需要在回调（WebClientX_DownloadDataCompleted）中处理数据。

public string[] SearchForMovie(string SearchParameter)
{
    WebClientX.DownloadDataCompleted += WebClientX_DownloadDataCompleted;
    WebClientX.DownloadDataAsync(new Uri(uri));
}

void WebClientX_DownloadDataCompleted(object sender,
     DownloadDataCompletedEventArgs e)
{
    Buffer = e.Result;
    string sitesearchSource = Encoding.ASCII.GetString(Buffer);
}

另外——不要假设 ASCII； WebClientX.Encoding 会更好；或者只是DownloadStringAsync:

static void Main()
{
    var client = new WebClient();
    client.DownloadStringCompleted += DownloadStringCompleted;
    client.DownloadStringAsync(new Uri("http://google.com"));
    Console.ReadLine();
}

static void DownloadStringCompleted(object sender,
    DownloadStringCompletedEventArgs e)
{
    if (e.Error == null && !e.Cancelled)
    {
        Console.WriteLine(e.Result);
    }
}