c# - 从 observablecollection 创建 observable

Question

我有 ObservableCollection 并且我需要创建 observable 如果集合包含任何元素则返回 true

我试着这样做

var collectionHasElementsObservable =
            Observable.FromEventPattern<NotifyCollectionChangedEventHandler,NotifyCollectionChangedEventArgs>(
                ev => ((ObservableCollection<MyType>)_items).CollectionChanged += ev,
                ev => ((ObservableCollection<MyType>)_items).CollectionChanged -= ev);

但我不知道如何将其转换为 IObservable

如何从中创建 observable ？

Answer 1

您可以使用Select 将事件映射到具有元素之一:

        ObservableCollection<int> coll = new ObservableCollection<int>();

        var hasElements = 
        Observable.FromEventPattern<NotifyCollectionChangedEventHandler,NotifyCollectionChangedEventArgs>(
            a => coll.CollectionChanged += a,
            a => coll.CollectionChanged -= a)
        .Select(_ => coll.Count > 0);

示例:

        hasElements.Subscribe(Console.WriteLine);

        coll.Add(1);
        coll.Add(2);
        coll.Remove(1);
        coll.Remove(2);

输出:

True
True
True
False

这就是您要找的吗？