Question

public interface INestedInterfaceTest<TChildType>
    where TChildType : INestedInterfaceTest<TChildType>
{
     List<TChildType> children { get; set; }
}

public abstract class NestedInterfaceTest : INestedInterfaceTest<NestedInterfaceTest>
{
    public List<NestedInterfaceTest> children { get; set; }

    public TNestedInterface GetNestedInterface<TNestedInterface>()
        where TNestedInterface : NestedInterfaceTest, new()
    {
        return GateWay<TNestedInterface>.GetNestedInterface();
    }
}

public class GateWay<TNestedInterface>
    where TNestedInterface : class, INestedInterfaceTest<TNestedInterface>, new()
{
    public static TNestedInterface GetNestedInterface()
    {
        return new TNestedInterface();
    }
}

抽象类中的GetNestedInterface方法出错了。错误消息是：类型'TNestedInterface'必须可转换为'INestedInterfaceTest'，以便在泛型类'GateWay'中将其用作参数'TNestedInterface'。

但是......，我的抽象类 NestedInterfaceTest 实现了 INestedInterfaceTest 接口。我在这里缺少什么？

以下工作正常，没有递归接口实现：

public interface INestedInterfaceTest
{
}

public abstract class NestedInterfaceTest : INestedInterfaceTest
{
    public List<NestedInterfaceTest> children { get; set; }

    public TNestedInterface GetNestedInterface<TNestedInterface>()
        where TNestedInterface : NestedInterfaceTest, new()
    {
        return GateWay<TNestedInterface>.GetNestedInterface();
    }
}

public class GateWay<TNestedInterface>
    where TNestedInterface : class, INestedInterfaceTest, new()
{
    public static TNestedInterface GetNestedInterface()
    {
        return new TNestedInterface();
    }
}

似乎在递归实现中出错了。

Answer 1

您在GetNestedInterface<>()上缺少通用约束。将其更改为：

public TNestedInterface GetNestedInterface<TNestedInterface>()
    where TNestedInterface : 
        NestedInterfaceTest, 
        INestedInterfaceTest<TNestedInterface>, // new
        new()
{
    return GateWay<TNestedInterface>.GetNestedInterface();
}

注意第二个约束是新的。

Answer 2

NestedInterfaceTest实施INestedInterfaceTest<NestedInterfaceTest>，而TNestedInterface中GetNestedInterface的要求是它应该实施INestedInterfaceTest<TNestedInterface>。

如果我创建的NestedInterfaceTest子类没有重新实现INestedInterfaceTest<>接口，则不会满足该约束：

//does not implement INestedInterfaceTest<Derived>
class Derived : NestedInterfaceTest {}
class Derived2 : NestedInterfaceTest {}

Derived d = new Derived();
// breaks because GateWay<Derived2> cannot be constructed
d.GetNestedInterface<Derived2>();

我认为，最简单的解决方法是，可能不适合您的对象模型的是使用以下内容重新定义GateWay类的约束：

public class GateWay<TNestedInterface>
  where TNestedInterface : class, INestedInterfaceTest<NestedInterfaceTest>, new()

这样，任何继承自NestedInterfaceTest的类都将满足约束而无需重新实现接口，因为NestedInterfaceTest实现了它。它可能更容易做到：

public class GateWay<TNestedInterface>
  where TNestedInterface : class, NestedInterfaceTest, new()

无论如何，即使你设法让它工作，它仍然令人困惑，无论是对于类的消费者，还是对于（最终的）维护者。此外，您几乎永远不会确定会发生一些误用not be possible

Answer 3

我想我解决了自己的问题。请查看代码并告诉我您的想法：

public interface INestedInterfaceTest<TChildType>
    where TChildType : INestedInterfaceTest<TChildType>
{
    List<TChildType> children { get; set; }
}

public abstract class NestedInterfaceTest<TChildNestedInterface> : INestedInterfaceTest<TChildNestedInterface>
    where TChildNestedInterface : INestedInterfaceTest<TChildNestedInterface>
{
    public List<TChildNestedInterface> children { get; set; }

    public virtual TNestedInterface GetNestedInterface<TNestedInterface>()
        where TNestedInterface : NestedInterfaceTest<TChildNestedInterface>, INestedInterfaceTest<TNestedInterface>, new()
    {
        return GateWay<TNestedInterface>.GetNestedInterface();
    }
}

public class GateWay<TNestedInterface>
    where TNestedInterface : class, INestedInterfaceTest<TNestedInterface>, new()
{
    public static TNestedInterface GetNestedInterface()
    {
        List<TNestedInterface> nestedChildren = new List<TNestedInterface>();
        return new TNestedInterface
            {
                children = nestedChildren
            };
    }
}

public class NestedClass : NestedInterfaceTest<NestedClass>
{
    public NestedClass GetNestedClass()
    {
        return GetNestedInterface<NestedClass>();
    }
}

这样做很好，它可以防止界面'漏出'。

类型'TNestedInterface'必须可转换为'INestedInterfaceTest'才能将其用作参数'TNestedInterface'

3 个答案: