How to call an async method from a getter or sette

Question

What'd be the most elegant way to call an async method from a getter or setter in C#?

Here's some pseudo-code to help explain myself.

async Task<IEnumerable> MyAsyncMethod()
{
    return await DoSomethingAsync();
}

public IEnumerable MyList
{
    get
    {
         //call MyAsyncMethod() here
    }
}

Answer 1

You can change the proerty to Task<IEnumerable>

and do something like:

get
{
    Task<IEnumerable>.Run(async()=>{
       return await getMyList();
    });
}

and use it like await MyList;

Answer 2

I think that we can await for the value just returning first null and then get the real value, so in the case of Pure MVVM (PCL project for instance) I think the following is the most elegant solution:

private IEnumerable myList;
public IEnumerable MyList
{
  get
    { 
      if(myList == null)
         InitializeMyList();
      return myList;
     }
  set
     {
        myList = value;
        NotifyPropertyChanged();
     }
}

private async void InitializeMyList()
{
   MyList = await AzureService.GetMyList();
}

Answer 3

One thing to note: In the case where an IEnumerable result is returned yield return is has better performance and does not require conversion to IEnumerable.

public IEnumerable MyList
    {
        get
        {
            yield return MyAsyncMethod();
        }
    }

Answer 4

Since your "async property" is in a viewmodel, you could use AsyncMVVM:

class MyViewModel : AsyncBindableBase
{
    public string Title
    {
        get
        {
            return Property.Get(GetTitleAsync);
        }
    }

    private async Task<string> GetTitleAsync()
    {
        //...
    }
}

It will take care of the synchronization context and property change notification for you.

Answer 5

You can't call it asynchronously, since there is no asynchronous property support, only async methods. As such, there are two options, both taking advantage of the fact that asynchronous methods in the CTP are really just a method that returns Task<T> or Task:

// Make the property return a Task<T>
public Task<IEnumerable> MyList
{
    get
    {
         // Just call the method
         return MyAsyncMethod();
    }
}

Or:

// Make the property blocking
public IEnumerable MyList
{
    get
    {
         // Block via .Result
         return MyAsyncMethod().Result;
    }
}

Answer 6

I thought .GetAwaiter().GetResult() was exactly the solution to this problem, no? eg:

string _Title;
public string Title
{
    get
    {
        if (_Title == null)
        {   
            _Title = getTitle().GetAwaiter().GetResult();
        }
        return _Title;
    }
    set
    {
        if (value != _Title)
        {
            _Title = value;
            RaisePropertyChanged("Title");
        }
    }
}