c# - 如何围绕类型协方差错误进行设计

Question

如何修正这个设计。错误，因为 C# 不允许类型协变。我如何改进或更正此设计

 public interface ITimeEvent
    {
    }

    public interface IJobTimeEvent : ITimeEvent
    {
    }

    public interface IActivityTimeEvent : ITimeEvent
    {
    }

    public interface IAssignmentTimeEvent<T> where T : ITimeEvent
    {
        T ParentTimeEvent
        {
            get;
            set;
        }
    }

    public class ScheduleJobTimeEvent : IAssignmentTimeEvent<IJobTimeEvent>
    {
        public IJobTimeEvent ParentTimeEvent
        {
           get;
           set;
        }
    }

    public class ScheduleActivityTimeEvent : IAssignmentTimeEvent<IActivityTimeEvent>
    {
        public IActivityTimeEvent ParentTimeEvent
        {
            get;
            set;
        }
    }

List<IAssignmentTimeEvent<ITimeEvent>> lst = new List<IAssignmentTimeEvent<ITimeEvent>>();
        lst.Add(new ScheduleJobTimeEvent());  //Error because C# doesn't allow Type Covariance
        lst.Add(new ScheduleActivityTimeEvent()); //Error because C# doesn't allow Type Covariance

Answer 1

C#4.0 和 .net4.0 确实允许泛型参数(在接口(interface)上)的协变或逆变。请参阅:http://msdn.microsoft.com/en-us/library/dd799517.aspx