public ClockViewModel()

in Clock/ViewModels/ClockViewModel.cs [12:20]


        public ClockViewModel(
            IClock clock,
            ITimer timer,
            IDispatcher dispatcher = null)
            :base(dispatcher)
        {
            _clock = clock ?? throw new ArgumentNullException(nameof(clock));
            _timerToken = (timer ?? throw new ArgumentNullException(nameof(timer))).Subscribe(this);
        }