在 .Net 中，为什么调用 Type.GetCustomAttributes(true) 时没有在返回的接口上声明属性？

发布于 2024-10-02 06:32:06 字数 724 浏览 1 评论 0原文

在回答这个问题时，我尝试使用 Type.GetCustomAttributes( true) 在实现接口的类上，该接口定义了属性。我惊讶地发现 GetCustomAttributes 没有返回接口上定义的属性。为什么不呢？接口不是继承链的一部分吗？

示例代码：

[Attr()]
public interface IInterface { }

public class DoesntOverrideAttr : IInterface { }

class Program
{
    static void Main(string[] args)
    {
        foreach (var attr in typeof(DoesntOverrideAttr).GetCustomAttributes(true))
            Console.WriteLine("DoesntOverrideAttr: " + attr.ToString());
    }
}

[AttributeUsage(AttributeTargets.All, Inherited = true)]
public class Attr : Attribute
{
}

输出：无

原文

In answer to this question I tried to use Type.GetCustomAttributes(true) on a class which implements an interface which has an Attribute defined on it. I was surprised to discover that GetCustomAttributes didn't return the attribute defined on the interface. Why doesn't it? Aren't interfaces part of the inheritance chain?

Sample code:

[Attr()]
public interface IInterface { }

public class DoesntOverrideAttr : IInterface { }

class Program
{
    static void Main(string[] args)
    {
        foreach (var attr in typeof(DoesntOverrideAttr).GetCustomAttributes(true))
            Console.WriteLine("DoesntOverrideAttr: " + attr.ToString());
    }
}

[AttributeUsage(AttributeTargets.All, Inherited = true)]
public class Attr : Attribute
{
}

Outputs: Nothing

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彡翼 2024-10-09 06:32:06

我不相信在实现的接口上定义的属性可以合理地继承。考虑这种情况：

[AttributeUsage(Inherited=true, AllowMultiple=false)]
public class SomethingAttribute : Attribute {
    public string Value { get; set; }

    public SomethingAttribute(string value) {
        Value = value;
    }
}

[Something("hello")]
public interface A { }

[Something("world")]
public interface B { }

public class C : A, B { }

由于该属性指定不允许出现多个，您希望如何处理这种情况？

I don't believe attributes defined on implemented interfaces can be reasonably inherited. Consider this case:

[AttributeUsage(Inherited=true, AllowMultiple=false)]
public class SomethingAttribute : Attribute {
    public string Value { get; set; }

    public SomethingAttribute(string value) {
        Value = value;
    }
}

[Something("hello")]
public interface A { }

[Something("world")]
public interface B { }

public class C : A, B { }

Since the attribute specifies that multiples are not allowed, how would you expect this situation to be handled?

回复收藏 0 原文

ゃ懵逼小萝莉 2024-10-09 06:32:06

因为类型 DoesntOverrideAttr 没有任何自定义属性。它实现的接口确实如此（请记住，类不是从接口继承的......它实现了它，因此在继承链上获取属性仍然不会包含来自接口的属性）：

// This code doesn't check to see if the type implements the interface.
// It should.
foreach(var attr in typeof(DoesntOverrideAttr)
                        .GetInterface("IInterface")
                        .GetCustomAttributes(true))
{
    Console.WriteLine("IInterface: " + attr.ToString());
}

Because the type DoesntOverrideAttr doesn't have any custom attributes. The Interface that it implements does (remember, a class doesn't inherit from an interface...it implements it so getting attributes up the inheritance chain still won't include attributes from interfaces):

// This code doesn't check to see if the type implements the interface.
// It should.
foreach(var attr in typeof(DoesntOverrideAttr)
                        .GetInterface("IInterface")
                        .GetCustomAttributes(true))
{
    Console.WriteLine("IInterface: " + attr.ToString());
}

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