WebClient 下载文件显示错误的百分比 [英] WebClient DownloadFile displaying wrong percentage

问题描述

我正在使用 System.Net.WebClient 在我的应用程序中异步下载文件.出于某种原因，在某些系统上，百分比计算错误.

I'm using a System.Net.WebClient to download a file asynchron in my application. For some reason, on some systems the percentage gets wrong calculated.

我的(更新的)DownloadProgressChanged 事件:

My (updated) DownloadProgressChanged event:

WebClient client = new WebClient();
client.DownloadProgressChanged += (_sender, _e) => {
    double bytesIn = _e.BytesReceived;
    double totalBytes = _e.TotalBytesToReceive;
    double percentage = bytesIn / totalBytes * 100;
    UpdateConnectingStatus("Missionsdatei wird heruntergeladen... (" + Math.Truncate(percentage).ToString() + "%)");
};

它应该是什么样子(Windows 8.1 64 位):

How it should look like (Windows 8.1 64bit):

它在某些系统上的外观(Windows 7 64 位):

How it looks on some systems (Windows 7 64bit):

会不会跟操作系统有关?或者有什么其他想法?

Could it have something to do with the OS? Or any other ideas?

更新:我完全删除了除法 (/1000000)，但它在同一系统上也不起作用.

UPDATE: I removed the division (/ 1000000) completly, but it doesn't work either on the same system.

更新 2:我检查了 totalBytes 的值.totalBytes 的结果在它不工作的系统上是 -1.任何想法为什么会这样?

UPDATE 2: I checked the value of totalBytes. The result of totalBytes is -1 on the system where it doesnt work. Any ideas why this is so?

更新 3:尽管我尝试删除字符串转换内容并将 .0 添加到除法中，但我仍然没有解决方案.我认为这取决于该人的互联网连接速度较慢，它对谁不起作用..我现在只显示百分比，如果它是正数.

UPDATE 3: I still don't have a solution although I tried to remove the string conversion stuff and adding a .0 to the division. I think it depends on the slow internet connection the person has, at whom it doesn't work.. I now only display the percentage, if it is positive.

推荐答案

根据一些网络搜索并根据我的反编译器 TotalBytesToReceive 如果下载的大小不是(还)可以是 -1已知.(是的，这是可怕的 API 设计.)

According to some web searching and according to my decompiler TotalBytesToReceive can be -1 if the size of the download is not (yet) known. (Yes, this is hideous API design.)

-1 情况的保护:

if (TotalBytesToReceive == -1)
 Print("Download in Progress");
else
 Print(e.ProgressPercent);

目前还不清楚为什么在那台机器上不知道下载大小.也许有一个 HTTP 代理删除了 Content-Length 标头，或者网络服务器由于某种原因没有发送它.

It is unclear yet why the download size is not known on that one machine. Maybe there is an HTTP proxy removing the Content-Length header, or the web server is not sending it for some reason.

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