c# – 通用处理程序的集合 – 这可能吗？

使用泛型是否可以将通用集合定义为基类型并分配子类型的实例？我在下面有一个简单的代码示例,突出了我的想法和导致编译器错误的行.我知道我可以创建一个IEventHandler标记接口,并使我的通用事件处理程序继承.这将允许我将泛型类型存储在IList的集合中,但这似乎不太理想.有没有类似于我下面的代码的方法？

using System;
using System.Collections.Generic;

namespace ConsoleApplication
{
    public class Program
    {
        public static void Main(string[] args)
        {
            IEventHandler<SomeEvent1> handler1 = new SomeEvent1Handler();
            IEventHandler<SomeEvent2> handler2 = new SomeEvent2Handler();


            IList<IEventHandler<IEvent>> handlers = new List<IEventHandler<IEvent>>();
            // COMPILE ERROR - is this possible?
            handlers.Add(new SomeEvent1Handler());
        }

        public interface IEvent {

        }

        public interface IEventHandler<in TEvent> where TEvent : IEvent 
        {
            void Handle(TEvent someEvent);
        }

        public class SomeEvent1 : IEvent {
        }
        public class SomeEvent2 : IEvent {
        }

        public class SomeEvent1Handler : IEventHandler<SomeEvent1>
        {
            public void Handle(SomeEvent1 someEvent)
            {
                throw new NotImplementedException();
            }
        }

        public class SomeEvent2Handler : IEventHandler<SomeEvent2>
        {
            public void Handle(SomeEvent2 someEvent)
            {
                throw new NotImplementedException();
            }
        }
    }

}

解决方法

Using generics is it possible to have a generic collection defined as
a base type and assign instances of a sub type?

是的,但只有你的界面是IEventHandler< out TEvent>才能完成,你不能用它来做.

如果您的代码确实有效,那么如果代码是什么,您会发生什么？

public static void Main(string[] args)
    {
        IList<IEventHandler<IEvent>> handlers = new List<IEventHandler<IEvent>>();
        handlers.Add(new SomeEvent1Handler()); //Magicly works
        IEventHandler<IEvent> handler = handlers[0];
        handler.Handle(new SomeEvent2());
    }

处理程序声明它允许任何IEvent传递给它的Handle函数.这会导致SomeEvent1Handler将SomeEvent2对象传递给其public void Handle(SomeEvent1 someEvent)方法.

我的工作就是让处理程序只需要一个IEvent,在它们检查的函数中是否是一种他们不关心的事件,他们只能从函数返回而不做任何事情.

using System;
using System.Collections.Generic;

namespace ConsoleApplication
{
    public class Program
    {
        public static void Main(string[] args)
        {
            IEventHandler<SomeEvent1> handler1 = new SomeEvent1Handler();
            IEventHandler<SomeEvent2> handler2 = new SomeEvent2Handler();


            IList<IEventHandler> handlers = new List<IEventHandler>();

            handlers.Add(new SomeEvent1Handler());
        }

        public interface IEvent {

        }

        public interface IEventHandler 
        {
            void Handle(IEvent someEvent);
        }

        public class SomeEvent1 : IEvent {
        }
        public class SomeEvent2 : IEvent {
        }

        public class SomeEvent1Handler : IEventHandler
        {
            public void Handle(IEvent someEvent)
            {
                var event = someEvent as SomeEvent1;
                if(event == null)
                    return;

                //Do stuff here.
            }
        }

        public class SomeEvent2Handler : IEventHandler
        {
            public void Handle(IEvent someEvent)
            {
                var event = someEvent as SomeEvent2;
                if(event == null)
                    return;

                //Do stuff here.
            }
        }
    }

}