Async Controller behaviour

Question

AsyncManager.Parameters["headlines"] = value; is assigning headlines value. But headlines are become null when NewsCompleted Method is being called.

public void NewsAsync(string city)
    {
        AsyncManager.OutstandingOperations.Increment();
        NewsService newsService = new NewsService();
        newsService.GetHeadlinesCompleted += (value) =>
        {
            AsyncManager.Parameters["headlines"] = value;
            AsyncManager.OutstandingOperations.Decrement();
        };
        newsService.GetHeadlinesAsync(city);
    }

    public ActionResult NewsCompleted(string[] headlines)
    {
        return View("News", new ViewStringModel
        {
            NewsHeadlines = headlines
        });
    }

1.)How can i debug this?

2.)And also when OutstandingOperations count become 0, framework calls my actionCompleted method, by requesting new thread from thread pool. When this actionCompleted method is called, I looked into call stack and have no idea that what is exactly happening behind. I mean how the framework knows it should call this particular actionCompleted method with this parameter from AsyncManager?

Thanks for the help.

Arghya C · Accepted Answer · 2013-07-27 07:17:14Z

1

Try these tweaks..

public void NewsAsync(string city)
{
    AsyncManager.OutstandingOperations.Increment();
    NewsService newsService = new NewsService();
    newsService.GetHeadlinesCompleted += (sender, args) =>
    {
        AsyncManager.Parameters["headlines"] = args.Result;
        AsyncManager.OutstandingOperations.Decrement();
    };
    newsService.GetHeadlinesAsync(city);
}

public ActionResult NewsCompleted(object headlines)
{
    return View("News", new ViewStringModel
    {
        NewsHeadlines = (string[])headlines
    });
}

answered Jul 27, 2013 at 7:17

Arghya C

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3 Comments

Al. Over a year ago

Its working fine for me. But why should I change from string[] to object to make it work?

Arghya C Over a year ago

AsyncManager.Parameters is a IDictionary<string, Object>. When you items add to this, it gets added as object for the string key passed.

Arghya C Over a year ago

If you are using mvc 4 (framework 4.5), you can use the new async await constructs, which will make the controller code much much cleaner.

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