如何使用 ImportMany 属性定义订单？
我刚刚进入 MEF，想知道如何定义使用 [ImportMany] 导出的集合的顺序？
我在这里的意思是，如果我有两个实现接口 IService 的类（Class1、Class2），并且每个实现都位于两个不同的库中（尽管它们可能位于同一个库中），我希望在IEnumerable 集合中的 Class1 实例由 ImportMany 属性定义。因此，它就像一个功能管道，其中 Class2 调用在 Class1 调用之前进行。
另外，我在另一个库中有另一个类（Class3，它也实现了 IService），我想稍后介绍它（即一些日志记录实用程序），如何使其成为 ImportMany 集合中的第三个实例？
I am just getting into MEF and was wondering how you could define the order of collection exported with [ImportMany]?
What I mean here is if I had two classes (Class1, Class2) that implement the interface IService and each of the implementations are in two different libraries (although they could be in the same), I want the Class2 instance to be created before the Class1 instance in the IEnumerable collection defined by the ImportMany attribute. So it is like a pipeline of functionality where Class2 calls are made before Class1 calls.
Also, I have an another Class (Class3 which also implements IService) in another library, which I want introduced later on (i.e. some logging utility), how do I make this the 3rd instance in the ImportMany collection?
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从 MEF 的角度来看，我认为您从错误的角度解决了这个问题。 MEF 鼓励接口和实现之间的分离。为了让消费者决定实现的顺序，它迫使消费者理解实现。
Visual Studio 采取的方法有点不同。它使用 OrderAttribute，通常组合使用使用 NameAttribute 让实现者指定一个订单。然后，使用者可以使用名称和顺序的组合对 ImportMany 的实现者进行排序，而无需了解底层实现。
From a MEF perspective I think you're approaching this problem from the wrong angle. MEF encourages a separation between interface and implementation. To have the consumer dictate the order of the implementations, it forces it to understand the implementation.
The approach taken by Visual Studio is a bit different. It uses the OrderAttribute, usually in combination with the NameAttribute to let the implementors specify an order. The consumer can then sort the implementors of an
ImportManyusing a combination of names and order without understanding the underlying implementation.您可以先“延迟”加载它们，然后在将它们添加到集合中时检查订单属性。
或者查看这个答案有一个例子说明了你正在尝试做的事情。
You'll could 'Lazy' load them first and then check an order attribute as you add them to a collection.
Or check out this answer which has an example of exacly what you're trying to do.