WebClient.OpenRead下载数据块

Question

我正在尝试使用Webclient对象在块5%的每个下载数据。原因是我需要报告每个下载块的进度。

下面是我写的代码来完成这个任务:

    private void ManageDownloadingByExtractingContentDisposition(WebClient client, Uri uri)
    {
        //Initialize the downloading stream 
        Stream str = client.OpenRead(uri.PathAndQuery);
        WebHeaderCollection whc = client.ResponseHeaders;
        string contentDisposition = whc["Content-Disposition"];
        string contentLength = whc["Content-Length"];
        string fileName = contentDisposition.Substring(contentDisposition.IndexOf("=") +1);
        int totalLength = (Int32.Parse(contentLength));
        int fivePercent = ((totalLength)/10)/2;
        //buffer of 5% of stream
        byte[] fivePercentBuffer = new byte[fivePercent];
        using (FileStream fs = new FileStream(fileName, FileMode.Create, FileAccess.ReadWrite))
        {
            int count;
            //read chunks of 5% and write them to file
            while((count = str.Read(fivePercentBuffer, 0, fivePercent)) > 0);
            {
                fs.Write(fivePercentBuffer, 0, count);
            }
        }
        str.Close();
    }

问题-当它到达str.Read()时，它暂停读取整个流，然后计数为0。因此，即使我指定只读取百分之五的变量，while()也不起作用。看起来它在第一次尝试中读取了整个流。

我怎样才能使它正确地读取块?

谢谢,

安德烈

Answer 1

在while循环的行尾有一个分号。我很困惑为什么被接受的答案是正确的，直到我注意到

Answer 2

do
{
    count = str.Read(fivePercentBuffer, 0, fivePercent);
    fs.Write(fivePercentBuffer, 0, count);
} while (count > 0);

Answer 3

如果你不需要精确的5%块大小，你可能想看看异步下载方法，如DownloadDataAsync或OpenReadAsync。

它们在每次下载新数据和进度变化时触发DownloadProgressChanged事件，并且该事件在事件参数中提供完成百分比。

一些示例代码:

WebClient client = new WebClient();
Uri uri = new Uri(address);
// Specify a progress notification handler.
client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(DownloadProgressCallback);
client.DownloadDataAsync(uri);
static void DownloadProgressCallback(object sender, DownloadProgressChangedEventArgs e)
{
    // Displays the operation identifier, and the transfer progress.
    Console.WriteLine("{0}    downloaded {1} of {2} bytes. {3} % complete...", 
        (string)e.UserState, 
        e.BytesReceived, 
        e.TotalBytesToReceive,
        e.ProgressPercentage);
}