CODEWITHSUNDEEP
asp.net-mvctaskworkflow-foundation-4async-await
Beats
Beats

Reputation: 201

Async ctp MVC4 and workflows

I have the below code which calls a workflow. I am wondering if I can changed the controller to be asynchronous using the async ctp.

public ActionResult Index()
    {
        var input = new Dictionary<string, object>();
        input["ViewData"] = this.ViewData;
        var userState = "BeginInvoke example";

        var invoker = new WorkflowInvoker(HelloMvcDefinition);

        Task workflowTask = Task.Factory.FromAsync<IDictionary<string, object>>(
            invoker.BeginInvoke(input, WorkflowCompletedCallback, userState),
            invoker.EndInvoke);

        workflowTask.Wait();

        return View();
    }

I have tried this but I cannot seem to get it to work:

public async Task<ActionResult> Index()
    {
        var input = new Dictionary<string, object>();
        input["ViewData"] = this.ViewData;
        var userState = "BeginInvoke example";

        var invoker = new WorkflowInvoker(HelloMvcDefinition);

        Task workflowTask = Task.Factory.FromAsync<IDictionary<string, object>>(
            invoker.BeginInvoke(input, WorkflowCompletedCallback, userState),
            invoker.EndInvoke);

        await workflowTask;

        return View();
    }

Unfortunately the view does not seem to work. Any ideas on what I am doing wrong?

EDIT After taking advice I have changed the method to this

public class HelloController : AsyncController
{
    private static readonly HelloWorkflow HelloMvcDefinition = new HelloWorkflow();

    public Task<ViewResult> Index()
    {
        var input = new Dictionary<string, object>();
        input["ViewData"] = ViewData;
        const string userState = "BeginInvoke example";

        var invoker = new WorkflowInvoker(HelloMvcDefinition);

        return Task.Factory.FromAsync<IDictionary<string, object>>(
            invoker.BeginInvoke(input, WorkflowCompletedCallback, userState),
            invoker.EndInvoke).ContinueWith(t => View());
    }       

    static void WorkflowCompletedCallback(IAsyncResult result)
    {

    }
}

Which works fine so the problem must be how I am using the async keyword.

Thanks

Upvotes: 0

Views: 874

Answers (2)

Twisha Desai
Twisha Desai

Reputation: 41

We can use the TAP pattern for invoking windows workflow as follows - (Details are mentioned in my blog post http://tweetycodingxp.blogspot.com/2013/06/invoke-workflow-wf-using-task-based.html)

public async Task<ActionResult> Index(string id)
{
    var wfInputArgs = new Dictionary<string, object>
    {
        ...
    };

    var wfOutputArgs = await Task<IDictionary<string, object>>.Factory.StartNew(
        () => WorkflowInvoker.Invoke(new MyWorkflow(), wfInputArgs));
    var result = wfOutputArgs["Output1"] as IEnumerable<Class1>;
    ...
    return View(model);
}

Upvotes: 1

Stephen Cleary
Stephen Cleary

Reputation: 457302

Derive from AsyncController instead of Controller.

EDIT: You may also be experiencing a known bug where ASP.NET MVC4 will hang if the action returns a completed Task. You can work around this bug by adding await Task.Yield(); at the top of the action method.

On an unrelated note, this code is more efficient (and shorter, too):

var workflowTask = Task.Factory.FromAsync(invoker.BeginInvoke, invoker.EndInvoke,
    input, userState);

Upvotes: 0

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