如何获取文件的大小（托管在Web服务器上）？

Question

I am using the WebClient class to download an .exe file from a web server. Here is the code I am using to download the file:

WebClient webClient = new WebClient();    
webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(webClient_DownloadProgressChanged);
webClient.DownloadDataAsync(new Uri("http://www.blah.com/calc.exe")); 

My application has a ProgressBar which gets updated in the callback ( webClient_DownloadProgressChanged ):

private void webClient_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
{
    progressBar.Value = (int)e.BytesReceived;
}

The problem I am having is I have to set the Maximum value for the progress bar dynamically. In other words I need to know the size of the file I am downloading before the download starts.

Is there a way to get the size of a file (before downloading it) given it's uri?

Answer 1

Try to set max size to e.TotalBytesToReceive like this

private void webClient_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
{
     progressBar.Max = (int)e.TotalBytesToReceive;
    progressBar.Value = (int)e.BytesReceived;

}

Answer 2

One of the ways will be checking for the Content-Length or the Range header in ResponseHeaders.

// To set the range
//webClient.Headers.Add("Range","bytes=-128");

// To read Content-Length
var bytes = Convert.ToInt64(webClient.ResponseHeaders["Content-Length"]);

Answer 3

If you only need to update progress bar correctly, the easiest way is to use ProgressPercentage

// progressBar.Max is always set to 100
progressBar.Value = e.ProgressPercentage;