Howto call back async function from rx subscribe?

Question

I would like to call back an async function within an Rx subscription.

E.g. like that:

public class Consumer
{
    private readonly Service _service = new Service();

    public ReplaySubject<string> Results = new ReplaySubject<string>();

    public void Trigger()
    {
        Observable.Timer(TimeSpan.FromMilliseconds(100)).Subscribe(async _ => await RunAsync());
    }

    public Task RunAsync()
    {
        return _service.DoAsync();
    }
}

public class Service
{
    public async Task<string> DoAsync()
    {
        return await Task.Run(() => Do());
    }

    private static string Do()
    {
        Thread.Sleep(TimeSpan.FromMilliseconds(200));
        throw new ArgumentException("invalid!");
        return "foobar";
    }
}

[Test]
public async Task Test()
{
    var sut = new Consumer();
    sut.Trigger();
    var result = await sut.Results.FirstAsync();
}

What needs to be done, in order to catch the exception properly?

Answer 1

Paul Betts' answer works in most scenarios, but if you want to block the stream while waiting for the async function to finish you need something like this:

Observable.Interval(TimeSpan.FromSeconds(1))
          .Select(l => Observable.FromAsync(asyncMethod))
          .Concat()
          .Subscribe();

Or:

Observable.Interval(TimeSpan.FromSeconds(1))
          .Select(_ => Observable.Defer(() => asyncMethod().ToObservable()))
          .Concat()
          .Subscribe();