当我们使用DownloadFileAsync时如何阻止主线程

Question

In my project I have a section to Download File . I use DownloadFileAsync() Method to Download and Add Two Event Handler :

• DownloadProgressChanged

• DownloadFileCompleted

I want when Use DownloadFileAsync to Download File ,Block main thread , because i don't want users can click on the button before download completed.

Part of my code:

WebClient webClient = new WebClient();
        webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChange);
        webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
        Uri Url = new Uri(txtUrl.Text.Trim());
        webClient.DownloadFileAsync(Url,FolderDialog.SelectedPath+System.IO.Path.GetFileName(txtUrl.Text) );

How can I do this ? I searched on the internet but I can't found useful Result. thanks

Answer 1

It's better to disable controls than to deliberately block the UI thread. In Windows Forms, this can be done by setting Control.Enabled to false . I'm not familiar with WPF so can't say what you'd do there. Anyway, disabling controls gets you the behavior you desire without stopping the normal processing of events, so the user can still move the window, it'll still repaint, etc.

Answer 2

You don't really need to disable the whole thread, just disable the button. If you really want to disable the main thread just call the thread.sleep but that defeats the purpose of downloading async as the end result is the same as downloading normally.

Answer 3

As others have said, in my experience the general way of doing this is:

1. Button is disabled before doing any downloading.
2. Download begins.
3. Download completion event handler enables the button again.
4. Additionally, in the event of a problem the button should be enabled.