如何防止WebClient冻结程序

Question

Currently I am using a webclient to download several XML files from a site. But for the duration of the download unity freezes up till these downloads finishes. Which take roughly 30 seconds, most of this time be taken up by the waitforsecond() call that the internal compiler makes, causing a 12*2 1 second wait calls.

Is there a way to bypass this/ run this on another thread but still being able to call it from unity?

 // the form is a login form
 public void PreObtainData(ref MonavisaRequestForm request, string dateAndTime, string fileDateAndTime)
    {
        if (!initialized)
            Initialize();
        try
        {
            if (!request.webclient.IsBusy && requestQueue.Count == 0)
            {
                request.url = request.url.Replace("&", "%26");
                request.url = request.url.Replace("+", "%2B");
                Uri uri = new Uri(string.Format("http://localhost/login.php?username={0}&password={1}&request={2}", request.username, request.password, request.url));
                request.webclient.DownloadFile(uri, @"Nioo Graph Data " + fileDateAndTime + ".xml");
            }
            else if (!request.webclient.IsBusy && requestQueue.Count > 0)
            {
                Uri uri = new Uri(string.Format("http://localhost/login.php?username={0}&password={1}&request={2}", requestQueue.Peek().username, requestQueue.Peek().password, requestQueue.Peek().url));
                requestQueue.Peek().webclient.DownloadFile(uri, @"Nioo Graph Data " + fileDateAndTime + ".xml");
                requestQueue.Dequeue();
            }
            else
            {
                requestQueue.Enqueue(request);
            }
        }
        catch (System.Net.WebException ex)
        {
            if (ex.Status != System.Net.WebExceptionStatus.ProtocolError)
            {
                throw;
            }
        }
    }

Answer 1

Instead of using a blocking method like DownloadFile you should use an asynchronous method like DownloadFileTaskAsync and the async/await keywords to ensure processing continues after the method returns data:

 // the form is a login form
public async Task PreObtainData(ref MonavisaRequestForm request, string dateAndTime, string fileDateAndTime)
{
    if (!initialized)
        Initialize();
    try
    {
        if (!request.webclient.IsBusy && requestQueue.Count == 0)
        {

            ...
            await request.webclient.DownloadFileTaskAsync(uri, @"Nioo Graph Data " + fileDateAndTime + ".xml");
        }
        else if (!request.webclient.IsBusy && requestQueue.Count > 0)
        {
            ...
            await requestQueue.Peek().webclient.DownloadFileTaskAsync(uri, @"Nioo Graph Data " + fileDateAndTime + ".xml");
            requestQueue.Dequeue();
        }
        else
        {
            requestQueue.Enqueue(request);
        }
    }
    catch (System.Net.WebException ex)
    {
        if (ex.Status != System.Net.WebExceptionStatus.ProtocolError)
        {
            throw;
        }
    }
}

This will convert PreObtainData to an asynchronous method as well. You should modify its caller to handle tasks as well. If this method is called inside an event handler, this can be done by changing the handler's signature to async void instead of void eg:

private async voidForm1_Load(object sender, System.EventArgs e)
{
    ...
    await PreObtainData(...);
    ...
}

Answer 2

Microsoft exposes a BackgroundWorker class in the System.ComponentModel namespace that is designed for precisely these kinds of operations. All you do is add a background worker to your form and capture the DoWork and RunWorkerCompleted events associated with it. You'll perform your downloads in the DoWork event and then perform any completion work and/or cleanup in the RunWorkerCompleted event.

As @Panagiotis indicated, I'm not sure your question has as much to do with Unity as it does with running a background process to prevent the main thread from locking up. Try out the BackgroundWorker and see if it accomplishes your goal.