c# - 该类型必须是引用类型才能将其用作泛型类型或方法中的参数 'T'

Question

我对泛型越来越深入，现在有一种情况需要帮助。如主题标题所示，我在下面的“派生”类上遇到编译错误。我看到许多其他与此类似的帖子，但我没有看到它们之间的关系。谁能告诉我如何解决这个问题？

using System;
using System.Collections.Generic;


namespace Example
{
    public class ViewContext
    {
        ViewContext() { }
    }

    public interface IModel
    {
    }

    public interface IView<T> where T : IModel 
    {
        ViewContext ViewContext { get; set; }
    }

    public class SomeModel : IModel
    {
        public SomeModel() { }
        public int ID { get; set; }
    }

    public class Base<T> where T : IModel
    {

        public Base(IView<T> view)
        {
        }
    }

    public class Derived<SomeModel> : Base<SomeModel> where SomeModel : IModel
    {

        public Derived(IView<SomeModel> view)
            : base(view)
        {
            SomeModel m = (SomeModel)Activator.CreateInstance(typeof(SomeModel));
            Service<SomeModel> s = new Service<SomeModel>();
            s.Work(m);
        }
    }

    public class Service<SomeModel> where SomeModel : IModel
    {
        public Service()
        {
        }

        public void Work(SomeModel m)
        {

        }
    }
}

Answer 1

我无法重现，但我怀疑在您的实际代码中某处有一个约束 T : class - 您需要传播它以使编译器快乐，例如(如果没有重现示例很难确定):

public class Derived<SomeModel> : Base<SomeModel> where SomeModel : class, IModel
                                                                    ^^^^^
                                                                 see this bit