Question

基本上我有一个接口IACollection定义一个参数IAItem的事件，然后是另一个继承自IACollection的接口IBCollection，它重新定义了这个事件以接受继承自IAItem的IBItem。

我的麻烦是，当我尝试创建一个实现接口IBCollection的类时，我似乎无法以一种真正只有一个实际事件的方式实现这两个事件 - 这是因为一个事件需要在IAItem中应该能够接受一个IBItem，因为它是一个IAItem。

以下是我对解决方案的两次尝试，但两者都因各种原因而失败。有没有办法实现我想要实现的目标？

using System;

public interface IAItem { }

public interface IBItem : IAItem { }

public interface IACollection
{
    event Action<IAItem> ItemAdded;
}

public interface IBCollection : IACollection
{
    new event Action<IBItem> ItemAdded;
}

public class Collection1 : IBCollection
{
    public event Action<IBItem> ItemAdded;

    // Won't work because the -= won't remove the same
    // lambda expression that was added before.
    event Action<IAItem> IACollection.ItemAdded
    {
        add { ItemAdded += (arg) => value(arg); }
        remove { ItemAdded -= (arg) => value(arg); }    // Won't remove
    }
}

public class Collection2 : IBCollection
{
    // Won't work in practice because Action<IB> cannot be
    // converted to Action<IA>, even though it should
    // theoretically work since IB can be converted to IA.
    public event Action<IBItem> ItemAdded
    {
        add { itemAdded += value; }     // Compile Error
        remove { itemAdded -= value; }      // Compile Error
    }

    event Action<IAItem> IACollection.ItemAdded
    {
        add { itemAdded += value; }
        remove { itemAdded -= value; }
    }

    private event Action<IAItem> itemAdded;
}

如何使用原始类型的子类型重新定义事件的参数类型并引用原始事件

0 个答案: