System.Reactive.AnonymousObserver<T> public sealed class AnonymousObserver<T> : ObserverBase<T> Class to create an IObserver<T> instance from delegate-based implementations of the On* methods. Documentation Code namespace System.Reactive { public sealed class AnonymousObserver<[System.Runtime.CompilerServices.Nullable(2)] T> : ObserverBase<T> { public AnonymousObserver(Action<T> onNext, Action<Exception> onError, Action onCompleted); public AnonymousObserver(Action<T> onNext); public AnonymousObserver(Action<T> onNext, Action<Exception> onError); public AnonymousObserver(Action<T> onNext, Action onCompleted); } }