WebClient DownloadDataAsync 当前下载速度

Question

我正在尝试获取 WebClient 下载文件的当前下载速度，但是当我使用一个我很确定应该可以解决的公式时：

Stopwatch.Stop();
double msElapsed = Stopwatch.Elapsed.TotalMilliseconds;
int bytesDownloaded = (int)e.BytesReceived - lastBytesDownloaded;
double downloadSpeed = (double)bytesDownloaded / (msElapsed / 1000);
lastBytesDownloaded = (int)e.BytesReceived;
Stopwatch.Restart();

Stopwatch 是我在开始文件下载时启动的秒表，lastBytesDownloaded 是一个类变量，这都在 downloadProgressChanged 事件中，但是下载速度与实际情况相差很大。

例如，如果我以 500kb/s 的速度下载文件，它会完全随机地从（例如）10kb/s 快速跳转到 50mb/s。

我可以通过对它进行几次编辑来获得准确的平均下载时间：

double sElapsed = Stopwatch.Elapsed.TotalSeconds;
int bytesDownloaded = (int)e.BytesReceived;
double downloadSpeed = bytesDownloaded / sElapsed;

但这不是我想要的。如何获得更稳定的当前下载速度读数？

Answer 1

您只需要smooth 较长时间的数据。例如，不要仅根据上次测量报告当前下载速度；请改用（可能是weighted）moving average。

简单的例子：

var measurements = 0, maxDataPoints = 5;
var dataPoints = new double[maxDataPoints];

然后：

Stopwatch.Stop();
double msElapsed = Stopwatch.Elapsed.TotalMilliseconds;
int bytesDownloaded = (int)e.BytesReceived - lastBytesDownloaded;
lastBytesDownloaded = (int)e.BytesReceived;
double dataPoint = (double)bytesDownloaded / (msElapsed / 1000);
dataPoints[measurements++ % maxDataPoints] = dataPoint;

double downloadSpeed = dataPoints.Average();
Stopwatch.Restart();