public TodoApp()
{
_todoItems = new ObservableCollection <TodoItem>();
AllTodoItems = new ReadOnlyObservableCollection <TodoItem>(_todoItems);
ActiveTodoItems = AllTodoItems.ToFilteredReadOnlyObservableCollection(x => !x.Completed.Value).AddTo(_disposables);
CompletedTodoitems = AllTodoItems.ToFilteredReadOnlyObservableCollection(x => x.Completed.Value).AddTo(_disposables);
IsCompletedAllItems = AllTodoItems.ObserveElementProperty(x => x.Completed)
.ToUnit()
.Merge(AllTodoItems.CollectionChangedAsObservable().ToUnit())
.Throttle(TimeSpan.FromMilliseconds(10))
.Select(_ => AllTodoItems.Count != 0 && AllTodoItems.All(x => x.Completed.Value))
.ToReadOnlyReactivePropertySlim()
.AddTo(_disposables);
}
