Unity/UniRx/値変更検知

IsCompletedが、trueになったときに、検知

hoge.ObserveEveryValueChanged(x => x.IsCompleted)
                .Subscribe(flag =>
                {
                    if (!IsCompleted) return;
                    Debug.Log("flag=" + flag);
                    Debug.Log("hoge.IsCompleted=" + hoge.IsCompleted); 
                })
                .AddTo(gameObject);