c# - 为什么下载文件时第二个文件在下载速度标签时显示无穷大符号？

Question

在屏幕截图中，下载速度 = 显示无穷大符号 kb/s 而不是速度。

速度标签显示第二个下载文件的无穷大符号，依此类推

第一个下载文件显示速度很好，但从第二个下载文件显示无穷大符号。如何修复它以便显示每个文件的速度？

下载方法：

private async Task DownloadAsync()
        {
            using (var client = new WebClient())
            {
                client.DownloadFileCompleted += (s, e) => lblStatus.Text = "Download File Completed.";
                client.DownloadFileCompleted += (s, e) => sw.Reset();
                client.DownloadProgressChanged += (s, e) => progressBar1.Value = e.ProgressPercentage;
                client.DownloadProgressChanged += (s, e) => lblAmount.Text = FormatBytes(e.BytesReceived);
                client.DownloadProgressChanged += (s, e) => lblSpeed.Text = string.Format("{0} kb/s", (e.BytesReceived / 1024d / sw.Elapsed.TotalSeconds).ToString("0.00"));
                client.DownloadProgressChanged += (s, e) => lblDownloadSize.Text = Convert.ToInt64(client.ResponseHeaders["Content-Length"]).ToString();
                client.DownloadProgressChanged += (s, e) =>
                {
                    lblDownloadProgress.Text = "%" + e.ProgressPercentage.ToString();
                    lblDownloadProgress.Left = Math.Min(
                        (int)(progressBar1.Left + e.ProgressPercentage / 100f * progressBar1.Width),
                        progressBar1.Width - lblDownloadProgress.Width
                    );
                };
                for (int i = 0; i < urls.Count; i++)
                {
                    await client.DownloadFileTaskAsync(new Uri(urls[i]), @"d:\satImages\img" + i + ".gif");
                }
            }
        }

格式化字节方法：

private string FormatBytes(long bytes)
        {
            string[] Suffix = { "B", "KB", "MB", "GB", "TB" };
            int i;
            double dblSByte = bytes;
            for (i = 0; i < Suffix.Length && bytes >= 1024; i++, bytes /= 1024)
            {
                dblSByte = bytes / 1024.0;
            }

            return String.Format("{0:0.00} {1}", dblSByte, Suffix[i]);
        }

并在一个按钮单击事件中启动它：

private async void btnStart_Click(object sender, EventArgs e)
        {
            lblStatus.Text = "Downloading...";
            sw.Start();
            await DownloadAsync();
        }