Question

I have a class (which I have no control over) that has a long running synchronous function which returns T. I want to make this asynchronous by changing it to an IObservable that will nothing while the function is running and then OnNext(T) -> OnCompleted(). What is the simplest way to implement this?

class Foo
{
  bool TakesAWhile();
}

class FooWrapper
{
  Foo foo;
  IObservable<bool> TakesAWhile()
  {
     // What goes here?
  }
}

The following works, but I suspect that I’m missing something nicer.

public IObservable<bool> TakesAWhile()
    {
    var s = new Subject<bool>();
    var worker = new BackgroundWorker();
    worker.DoWork += (sender, e) =>
       {
            s.OnNext(foo.TakesAWhile());
            s.OnCompleted();
        };
    worker.RunWorkerAsync();
    return s.AsObservable<bool>();
}

Answer 1

It’s simple – just use .Start().

Try something like this:

Func<int> fn = () => 42;
IObservable<int> ofn = Observable.Start<int>(fn);
ofn.Subscribe(n =>
{
    Console.WriteLine(n);
});

In your code you’re looking for this:

IObservable<bool> TakesAWhile()
{
    return Observable.Start<bool>(foo.TakesAWhile);
}