Progress bar and webclient

问题:

I have an event that takes about 10-30 seconds, namely downloading information from a page (with quite a lot of traffic), modifying it and then saving it somewhere onto the disk using WebClient. Because it takes such a long time, I want to add a progress bar or make an update label (which says something like updating..) to indicate the progress.

Can someone guide me as to how I would do this? Is there any event in the WebClient I can use to handle this?

回答1:

If you're writing a Windows Forms client application (not a ASP.NET server-side component), showing the progress of a WebClient download can be done as follows:

WebClient webClient = new WebClient();
webClient.DownloadProgressChanged += (s, e) =>
{
    progressBar.Value = e.ProgressPercentage;
};
webClient.DownloadFileCompleted += (s, e) =>
{
    progressBar.Visible = false;
    // any other code to process the file
};
webClient.DownloadFileAsync(new Uri("http://example.com/largefile.dat"),
    @"C:\Path\To\Output.dat");

(progressBar is the ID of a ProgressBar object on your form.)