[EN] [ASP.NET MVC 4] Asynchronous controllers
29 Sep 2011 in ASP.NET MVCAsynchronous execution is the future of Windows development : it has been largely demonstrated during the //Build conference two weeks ago.
In previous versions of ASP.NET MVC it was possible to create asynchronous controllers by inheriting the AsyncController class and using some conventions :
- MyActionAsync : method that returns void and launches an asynchronous process
- MyActionCompleted : method that returns an ActionResult (the result of the MVC action
MyAction, in this case)
To allow the MVC engine to manage asynchronous operations and pass the result to the view engine, developers had to use the propery AsyncManager of the AsyncController. The completed method parameters was passed by the MVC engine through this object.
For example, the controller that is defined bellow allows to get a Json-serialized list of movies – asynchronously – from an OData service :
public class MoviesController : AsyncController
{
public ActionResult Index()
{
return View();
}
public void GetJsonMoviesAsync(int? page)
{
const int pageSize = 20;
int skip = pageSize * ((page ?? 1) - 1);
string url = string.Format("http://odata.netflix.com/[…]&$skip={0}&$top={1}",
skip, pageSize);
//the asynchronous operation is declared
AsyncManager.OutstandingOperations.Increment();
var webClient = new WebClient();
webClient.DownloadStringCompleted += OnWebClientDownloadStringCompleted;
webClient.DownloadStringAsync(new Uri(url));//the asynchronous process is launched
}
private void OnWebClientDownloadStringCompleted(object sender,
DownloadStringCompletedEventArgs e)
{
//the asynchronous process ends
//"movies" result is added to the parameters of the AsyncManager
//NB : it's the name of the parameter that is take by the
//GetJsonMoviesCompleted method
List<Movie> movies = null;
if (AsyncManager.Parameters.ContainsKey("movies"))
{
movies = (List<Movie>)AsyncManager.Parameters["movies"];
movies.Clear();
}
else
{
movies = new List<Movie>();
AsyncManager.Parameters["movies"] = movies;
}
movies.AddRange(Movie.FromXml(e.Result));
//the ends of the asynchronous operation (launches the call of "Action"Completed)
AsyncManager.OutstandingOperations.Decrement();
}
public ActionResult GetJsonMoviesCompleted(List<Movie> movies)
{
//on retourne le résultat Json
return Json(movies, JsonRequestBehavior.AllowGet);
}
}
It’s not really complicated to create an asynchronous controller but ASP.NET MVC 4 and C# 5 with the new async and await keywords will make it easier !
public class MoviesController : AsyncController
{
public ActionResult Index()
{
return View();
}
public async Task<ActionResult> GetJsonMovies(int? page)
{
const int pageSize = 20;
int skip = pageSize * ((page ?? 1) - 1);
string.Format("http://odata.netflix.com/[…]&$skip={0}&$top={1}",
skip, pageSize);
var webClient = new WebClient();
string xmlResult = await webClient.DownloadStringTaskAsync(url);
return Json(Movie.FromXml(xmlResult), JsonRequestBehavior.AllowGet);
}
}
As you can see in the previous code snippet, in ASP.NET MVC 4 you always should inherits from AsyncController but there is no more naming conventions, no more Async/Completed methods, no more AsyncManager and the action returns a Task
It’s awesome !
Hope this helps 