有没有一种更聪明的办法不是忙等待检查System.Net.WebClient.DownloadFileAsync下载完成（）？ [英] Is there a smarter way than a busy-wait to check for download completion of System.Net.WebClient.DownloadFileAsync()?

问题描述

我在下载使用System.Net.WebClient.DownloadFileAsync文件（）。用于使用异步版本的唯一原因是显示下载的进度。 我的code的执行可能无法继续100％，已经达到了。目前我使用一个忙等待（见code），但我不知道是否有一个更聪明的方法来做到这一点。

 使用（WebClient的oWebClient =新的Web客户端（））
{
    oWebClient.Encoding = System.Text.Encoding.UTF8;
    长lReceived = 0;
    长LTOTAL = 0;
    //设置一个委托观看下载进度。
    oWebClient.DownloadProgressChanged + =委托（对象发件人，DownloadProgressChangedEventArgs E）
    {
        Console.WriteLine（e.ProgressPercentage +％（+ e.BytesReceived / 1024f + e.TotalBytesToReceive / 1024f +KB）的KB）;
            //分配给外部变量，允许忙等待检查。
        lReceived = e.BytesReceived;
        LTOTAL = e.TotalBytesToReceive;
    };
    oWebClient.DownloadFileAsync（新的URI（SURL + sPostData），sTempFile？）;
    而（lReceived == 0 || lReceived！= LTOTAL）
    {
           //忙等待。
        Thread.sleep代码（1000）;
    }
}
 

解决方案

 使用（WebClient的oWebClient =新的Web客户端（））
{
    //使用一个事件的等待，而不是一个Thread.sleep（）方法循环。
    VAR通知=新的AutoResetEvent（假）;

    oWebClient.Encoding = System.Text.Encoding.UTF8;
    长lReceived = 0;
    长LTOTAL = 0;
    //设置一个委托观看下载进度。
    oWebClient.DownloadProgressChanged + =委托（对象发件人，DownloadProgressChangedEventArgs E）
    {
        Console.WriteLine（e.ProgressPercentage +％（+ e.BytesReceived / 1024f + e.TotalBytesToReceive / 1024f +KB）的KB）;
        //分配给外部变量，允许忙等待检查。
        lReceived = e.BytesReceived;
        LTOTAL = e.TotalBytesToReceive;

        //表明，做事情
        如果（lReceived＆GT; = LTOTAL）notifier.Set（）;
    };

    oWebClient.DownloadFileAsync（新的URI（SURL + sPostData），sTempFile？）;

    //等待信号进行
    notifier.WaitOne（）;
}
 

I'm downloading a file using System.Net.WebClient.DownloadFileAsync(). The only reason for using the async version is to show the progress of the download. My code execution may not continue before 100% have been reached. Currently I'm using a busy-wait (see code) but I wonder if there is a smarter way to do it.

using(WebClient oWebClient = new WebClient())
{
    oWebClient.Encoding = System.Text.Encoding.UTF8;
    long lReceived = 0;
    long lTotal = 0;
    // Set up a delegate to watch download progress.
    oWebClient.DownloadProgressChanged += delegate(object sender, DownloadProgressChangedEventArgs e)
    {
        Console.WriteLine(e.ProgressPercentage + "% (" + e.BytesReceived / 1024f + "kb of " + e.TotalBytesToReceive / 1024f + "kb)");
            // Assign to outer variables to allow busy-wait to check.
        lReceived = e.BytesReceived;
        lTotal = e.TotalBytesToReceive;
    };
    oWebClient.DownloadFileAsync(new Uri(sUrl + "?" + sPostData), sTempFile);
    while(lReceived == 0 || lReceived != lTotal)
    {
           // Busy wait.
        Thread.Sleep(1000);
    }
}

解决方案

using(WebClient oWebClient = new WebClient())
{
    // use an event for waiting, rather than a Thread.Sleep() loop.
    var notifier = new AutoResetEvent(false);

    oWebClient.Encoding = System.Text.Encoding.UTF8;
    long lReceived = 0;
    long lTotal = 0;
    // Set up a delegate to watch download progress.
    oWebClient.DownloadProgressChanged += delegate(object sender, DownloadProgressChangedEventArgs e)
    {
        Console.WriteLine(e.ProgressPercentage + "% (" + e.BytesReceived / 1024f + "kb of " + e.TotalBytesToReceive / 1024f + "kb)");
        // Assign to outer variables to allow busy-wait to check.
        lReceived = e.BytesReceived;
        lTotal = e.TotalBytesToReceive;

        // Indicate that things are done
        if(lReceived >= lTotal) notifier.Set();
    };

    oWebClient.DownloadFileAsync(new Uri(sUrl + "?" + sPostData), sTempFile);

    // wait for signal to proceed
    notifier.WaitOne();
}

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