该类型必须是引用类型，才能在泛型类型或方法使用它作为参数'T' [英] The type must be a reference type in order to use it as parameter 'T' in the generic type or method

问题描述

我越来越深入到仿制药，现在有一个情况我需要帮助。我得到如下图所示的主旨题的派生类的编译错误。我看到类似这样的许多其他职位，但我没有看到的关系。谁能告诉我怎么解决这个问题？

 使用系统;
使用System.Collections.Generic;
命名空间示例
{
    公共类ViewContext
    {
        ViewContext（）{}
    }    公共接口IModel
    {
    }    公共接口IVIEW＆LT; T＆GT;其中T：IModel
    {
        ViewContext ViewContext {搞定;组; }
    }    公共类SomeModel：IModel
    {
        公共SomeModel（）{}
        公众诠释ID {搞定;组; }
    }    公共类基地＆LT; T＆GT;其中T：IModel
    {        公共库（IVIEW＆LT; T＆gt;查看）
        {
        }
    }    公共类派生＆LT; SomeModel＆GT; ：基地＆LT; SomeModel＆GT;其中，SomeModel：IModel
    {        公共派生（IVIEW＆LT; SomeModel＆gt;查看）
            ：基地（视图）
        {
            SomeModel M =（SomeModel）Activator.CreateInstance（typeof运算（SomeModel））;
            服务与LT; SomeModel＆GT; S =新的服务和LT; SomeModel＆GT;（）;
            s.Work（米）;
        }
    }    公共类服务与LT; SomeModel＆GT;其中，SomeModel：IModel
    {
        公共服务（）
        {
        }        公共无效工作（SomeModel米）
        {        }
    }
}
 

解决方案

我不能瑞普，但我的犯罪嫌疑人的，在实际code是有约束的地方， T：类 - 你需要的传播，使编译器高兴，例如（很难说肯定没有一个摄制为例）：

 公共类派生＆LT; SomeModel＆GT; ：基地＆LT; SomeModel＆GT;其中，SomeModel：类，IModel
                                                                    ^^^^^
                                                                 看到此位
 

I'm getting deeper into generics and now have a situation I need help with. I get a compile error on the 'Derived' class below as shown in the subject title. I see many other posts similar to this one but I'm not seeing the relationship. Can someone tell me how to resolve this?

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)
        {

        }
    }
}

解决方案

I can't repro, but I suspect that in your actual code there is a constraint somewhere that T : class - you need to propagate that to make the compiler happy, for example (hard to say for sure without a repro example):

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

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