如何观察物品的集合是否有效？

Question

我正在使用ReactiveUI和提供的ReactiveCollection<>类.

在ViewModel中我有一组对象,我希望创建一个observable来监视这些项目的IsValid属性.

这是我想要解决的方案.在我的ViewModel的构造函数中.

this.Items = new ReactiveCollection<object>();

IObservable<bool> someObservable = // ... how do I watch Items so when 
                                   // any items IsValid property changes, 
                                   // this observable changes. There
                                   // is an IValidItem interface.

this.TheCommand = new ReactiveCommand(someObservable);

...

interface IValidItem { bool IsValid { get; } }

编辑保罗的回答让我大部分都在那里.解决方案如下.

this.Items = new ReactiveCollection<object>();
this.Items.ChangeTrackingEnabled = true;

var someObservable = this.Items.Changed
    .Select(_ => this.Items.All(i => i.IsValid));

Answer 1

这取决于你想对IsValid的结果做什么.这是我将如何做到这一点,虽然它并不完全直观:

// Create a derived collection which are all the IsValid properties. We don't
// really care which ones are valid, rather that they're *all* valid
var isValidList = allOfTheItems.CreateDerivedCollection(x => x.IsValid);

// Whenever the collection changes in any way, check the array to see if all of
// the items are valid. We could probably do this more efficiently but it gets
// Tricky™
IObservable<bool> areAllItemsValid = isValidList.Changed.Select(_ => isValidList.All());

theCommand = new ReactiveCommand(areAllItemsValid);