How to convert callbacks to Rx.Observable? - system.reactive

Question

If an external library offers only to register a callback instead of an event, what is the best way to create an Observable from it?
If it where an event I could use Observable.FromEventPattern but in this case the only idea I have is to use a Subjectand queue events in it on each callback.
Is there any better way to do this?

Answer 1

Use Observable.Create. Here's an example:
void Main()
{
var target = new SampleCallbacker();
var actionB = new Action<int>(i => Console.WriteLine($"{i} * {i} = {i * i}."));
target.Register(actionB);
var observable = Observable.Create<int>(observer =>
{
var action = new Action<int>(i => observer.OnNext(i));
target.Register(action);
return () => target.Unregister(action);
});
var subscription = observable.Subscribe(i => Console.WriteLine($"From observable: {i} was fired."));
target.Fire(1);
target.Fire(2);
target.Fire(3);
Console.WriteLine("Unsusbscribing observable...");
subscription.Dispose();
target.Fire(4);
target.Fire(5);
}
class SampleCallbacker
{
private List<Action<int>> _actions = new List<System.Action<int>>();
public void Register(Action<int> action)
{
_actions.Add(action);
}
public void Unregister(Action<int> action)
{
while (_actions.Remove(action))
{} //loop remove
}
public void Fire(int i)
{
foreach (var action in _actions)
{
action(i);
}
}
}