使用WebClient（）计算要下载的总字节数

变量’totalBytes’始终为-1，因此我无法正确计算/更新进度条，为什么会发生这种情况？

private void button1_Click(object sender, EventArgs e) { WebClient client = new WebClient(); client.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed); client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged); client.DownloadFileAsync(new Uri("http://example.com/test.mp3"), @"E:\Test.mp3"); } private void ProgressChanged(object sender, DownloadProgressChangedEventArgs e) { double bytesIn = double.Parse(e.BytesReceived.ToString()); label1.Text = Convert.ToString(bytesIn); double totalBytes = double.Parse(e.TotalBytesToReceive.ToString()); //stays at -1 label2.Text = Convert.ToString(totalBytes); double percentage = bytesIn / totalBytes * 100; label3.Text = Convert.ToString(percentage); progressBar1.Value = int.Parse(Math.Truncate(percentage).ToString()); } 

Answer 1

WebClient内部使用WebRequest ，问题可能是您从中下载文件的服务器没有发送Content-Length HTTP标头，在这种情况下，您应该使用Indeterminate ProgressBar样式（例如Marquee）。

Answer 2

您可以在响应标头中手动检查Content-Length

 client.ResponseHeaders["Content-Length"]