Question

I am using async and await in a controller.

The following code works fine

[HttpPost]
[ValidateAntiForgeryToken]        
public async Task<ActionResult> Create(CompetitionViewModel viewModel)
{
        if (ModelState.IsValid)
        {

            User user = null;
            using (var facebookClient = new FacebookClient(viewModel.AccessToken))
            {
                var facebookUser = await facebookClient.Me();
                user = entityStorage.GetUser(facebookUser);
                FormsAuthentication.SetAuthCookie(user.FacebookId, true);
            }

However if I try and execute the same code in an extension method then the await never completes.

[HttpPost]
[ValidateAntiForgeryToken]        
public ActionResult Create(CompetitionViewModel viewModel)
{
    if (ModelState.IsValid)
    {
        var user = entityStorage.GetCurrentUser(viewModel.AccessToken).Result;

and

public static class Helpers
    {
        public async static Task<User> GetCurrentUser(this IEntityStorage entityStorage, string accessToken)
        {
            User user = null;
            using (var facebookClient = new FacebookClient(accessToken))
            {
                var facebookUser = await facebookClient.Me(); //STUCK HERE!!
                user = entityStorage.GetUser(facebookUser);
                FormsAuthentication.SetAuthCookie(user.FacebookId, true);
            }
            return user;
        }

I am using MVC4 and have <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" /> set in my web.config as per other threads suggestions.

Can anyone tell me why this is and how I can get it to work?

Answer 1

I have a blog post that covers this in detail.

In short, you are causing a deadlock by calling Result. Instead, make your Create method async and use await to get the user.:

[HttpPost]
[ValidateAntiForgeryToken]        
public async Task<ActionResult> Create(CompetitionViewModel viewModel)
{
  if (ModelState.IsValid)
  {
    var user = await entityStorage.GetCurrentUser(viewModel.AccessToken);