addStateListener
abstract fun addStateListener(subscriptionContainer: DisposableSubscriptionContainer, listener: Session.StateListener<F>): DisposableSubscription
Adds a StateListener to this session if it's not registered yet and appends the subscription to the subscriptions bag. The listener will be notified with current state immediately upon registering.
Listeners are notified on main thread.
Return
DisposableSubscription — a handle to the subscription, dummy object if listener is already registered.