Create observable and consume only between events

Question

Imagine the following scenario:

I have this events:

• AfterLogin
• BeforeLogoff

And AfterLogin, I have others events, based on new/others objects available..

When the user make a login, I need to create a new subscription and subscribe or handle it (using others events).
When the user make a logoff, I need dispose these subscriptions and wait for AfterLogin again

It is very similar to: Between values with Rx
The big diference that it is necessary a "factory" to create a subscription and dispose more later, I can't listen the source at the begin.

How can I handle this?

Answer 1

Since you have provided no code and the specification is a little vague, it's hard to give a specific code example, so this is a little scrappy.

But perhaps it will provide some inspiration or guide you to a more specific question. Posting some of what you have tried always helps!

The code gives you a single non-terminated stream that carries all events generated by logged in users across all sessions.

public class LoggedInActivity
{
    [Test]
    public void TestLoggingIn()
    {
        var sessionManager = new SessionManager();

        var afterLogIn = Observable.FromEventPattern<SessionEventArgs>(
            h => sessionManager.AfterLogin += h,
            h => sessionManager.AfterLogin -= h)
            .Select(x => x.EventArgs.UserId);

        var beforeLogOff = Observable.FromEventPattern<SessionEventArgs>(
            h => sessionManager.BeforeLogoff += h,
            h => sessionManager.BeforeLogoff -= h)
            .Select(x => x.EventArgs.UserId);

        var loggedIn = afterLogIn.GroupByUntil(
            userId => userId,
            login => beforeLogOff.Where(y => y == login.Key));

        Func<IGroupedObservable<int, int>, IObservable<string>> whileLoggedIn = login =>
            Observable.Using(
                () => sessionManager.AddSession(new Session(login.Key)),
                session => Observable.FromEventPattern(
                    h => session.SomeEvent += h,
                    h => session.SomeEvent -= h)
                    .Select(x => "User " + login.Key + " had SomeEvent!")
                    .TakeUntil(login.LastAsync()));

        // Single non-terminating stream that captures
        // all events occuring during any login 
        var loggedInEvents = loggedIn.SelectMany(whileLoggedIn);

        loggedInEvents.Subscribe(Console.WriteLine);

        sessionManager.Login(1);
        sessionManager.Sessions[1].RaiseSomeEvent();
        sessionManager.Login(2);
        sessionManager.Sessions[1].RaiseSomeEvent();
        sessionManager.Sessions[2].RaiseSomeEvent();
        sessionManager.Logoff(2);
        sessionManager.Logoff(1);

    }
}

public class SessionManager
{
    public event EventHandler<SessionEventArgs> AfterLogin;
    public event EventHandler<SessionEventArgs> BeforeLogoff;

    private readonly Dictionary<int, Session> _sessions = new Dictionary<int, Session>();
    public Dictionary<int, Session> Sessions { get { return _sessions; } }

    public void Login(int userId)
    {
        var temp = AfterLogin;
        if (temp != null)
        {
            AfterLogin(this, new SessionEventArgs(userId));
        }
    }

    public Session AddSession(Session session)
    {
        _sessions.Add(session.UserId, session);
        return session;
    }

    public void Logoff(int userId)
    {
        var temp = BeforeLogoff;
        if (temp != null)
        {
            BeforeLogoff(this, new SessionEventArgs(userId));
        }

        Sessions.Remove(userId);

    }
}

public class Session : IDisposable
{
    private readonly int _userId;

    public int UserId { get { return _userId; } }

    public Session(int userId)
    {
        _userId = userId;
        Console.WriteLine("User " + _userId + " logged in.");
    }

    public event EventHandler SomeEvent;

    public void RaiseSomeEvent()
    {
        var temp = SomeEvent;
        if (temp != null)
        {
            SomeEvent(this, EventArgs.Empty);
        }
    }

    public void Dispose()
    {
        Console.WriteLine("User " + _userId + " logged out.");
    }
}

public class SessionEventArgs : EventArgs
{
    private readonly int _userId;

    public SessionEventArgs(int userId)
    {
        _userId = userId;
    }

    public int UserId { get { return _userId; } }
}

Session instances and the observable streams of their events are created on login and get disposed on logoff.

The output from running the test is:

User 1 logged in.
User 1 had SomeEvent!
User 2 logged in.
User 1 had SomeEvent!
User 2 had SomeEvent!
User 2 logged out.
User 1 logged out.