How to link IObservable and IObserver in C#?

I've been studying Observer parttern since this morning, but can't seem to figure out how to implement it with the built-in interfaces. I already looked at some examples but couldn't find any simple example yet.

Here's my code so far, inspired by the Microsoft Documentation :

class ObservableClass : IObservable<bool>, IDisposable { public bool observableBool; public List<IObserver<bool>> observers; public ObservableClass() { this.observableBool = false; this.observers = new List<IObserver<bool>>(); } public IDisposable Subscribe(IObserver<bool> observer) { if (!observers.Contains(observer)) { AddObserver(observer); } return this; } public void Dispose() { Console.WriteLine("Disposing..."); } public void AddObserver(IObserver<bool> obs) { this.observers.Add(obs); } public void RemoveObserver(IObserver<bool> obs) { this.observers.Remove(obs); } public void SwapBool() { observableBool = !observableBool; } } 

the observable class contains an observableBool field. I want to notify the Observer when that field changes value.

Here's my Observer :

class ObserverClass : IObserver<bool> { public IDisposable observable; public void OnCompleted() { Console.WriteLine("Completed"); } public void OnError(Exception error) { Console.WriteLine("error"); } public void OnNext(bool value) { Console.WriteLine("Next"); } public virtual void Subscribe(IObservable<bool> obs) { if (obs != null) observable = obs.Subscribe(this); } public void stopObserve() { observable.Dispose(); } } 

And finally my Program :

static void Main(string[] args) { ObservableClass observable = new ObservableClass(); ObserverClass observer = new ObserverClass(); observer.Subscribe(observable); Console.WriteLine("subscribed observer"); observable.SwapBool(); Console.WriteLine("performed swapBool"); } 

Expected output :

subscribed observer Completed //Returned by ObserverClass.OnComplete() performed swapBool 

How to make this work ? How to call on OnComplete and the other methods of ObserverClass everytime observableBool changes ?

I know there are other ways to do that, but my goal is to be able to use IObserver and IObservable.

1 Answer

You iterate over your set of observables to notify them:

public void SwapBool() { observableBool = !observableBool; foreach (observable in observers) { observable.OnNext(observableBool); } } 

You are meant to call OnNext when there is a new value. OnComplete is used to notify that there will be no more values.

I just noticed your observable is IDisposable...

First of all, disposing the result of Subscribe should unsubscribe that observer. Not dispose the observable.

In fact, I would expect that disposing the observable means that it will no longer be sending values (calls OnComplete on everybody and releases the list of observers).

Other concerns include:

• You probably want a set type so you can add and remove observables more efficiently.
• List is not thread-safe.
• Why are you exposing your fields?