Using Rx Framework for async calls using the void AsyncMethod(Action callback) pattern

Question

I\'ve seen tons of examples on how to use the Observable.FromAsyncPattern() in the Rx Framework to simplify Async calls, but I\'m using an interface that doesn\'t use the st

Answer 1

Try Observable.Create(), perhaps something like this:

public IObservable<Object> ObserveAllObjects()
{
    return Observable.Create<Object>(
        observer =>
            () => GetAllObjects(objects => objects.ForEach(o => observer.OnNext(o))));
}

Answer 2

I like Observable.Create for this, but @dahlbyk answer is incorrect(misses completion and performs the action in the unsubscribe handler). Should be something like this:

    IObservable<List<T>> FromListCallbackPattern<T>(
        Action<Action<List<T>>> listGetter)
    {
        return Observable
            .Create<List<T>>(observer =>
            {
                var subscribed = true;
                listGetter(list =>
                {
                    if (!subscribed) return;
                    observer.OnNext(list);
                    observer.OnCompleted();
                });
                return () =>
                {
                    subscribed = false;
                };
            });
    }

Also, since the originating API returns an entire list altogether, I don't see a reason to transform it to observable too early. Let the resulting observable return a list as well, and if a caller needs to flatten it, he can use .SelectMany

Answer 3

Func<IObservable<TRet>> FromListCallbackPattern(Action<Action<List<TRet>>> function)
{
    return () => {
        // We use a ReplaySubject so that if people subscribe *after* the
        // real method finishes, they'll still get all the items
        ret = new ReplaySubject<TRet>();

        function((list) => {
            // We're going to "rebroadcast" the list onto the Subject
            // This isn't the most Rx'iest way to do this, but it is the most
            // comprehensible :)
            foreach(var v in list) {
                ret.OnNext(v);
            }
            ret.OnCompleted();
        });

        return ret;
    };
}

Now, you can do something like:

var getAllUsers = FromListCallbackPattern(mClient.GetAllUsers);
getAllUsers().Subscribe(x => /* ... */);