GetCustomAttributes继承参数与AttributeUsage.Inherited

Question

为什么GetCustomAttributes(true)不返回AttributeUsageAttribute.Inherited = false(AttributeUsageAttribute.Inherited = false)的属性(https://msdn.microsoft.com/query/dev14.query?appId=Dev14IDEF1&l=EN-US&k=k(System.AttributeUsageAttribute.Inherited%29;k(TargetFrameworkMoniker-.NETFramework,Version%3Dv4.6.1%29;k(DevLang-csharp%29&rd=true)?文档中没有提到这两者应该相互作用的东西)。下面的代码输出0。

class Program
{

    [AttributeUsage(AttributeTargets.Class, Inherited = false)]
    class NotInheritedAttribute : Attribute { }

    [NotInherited]
    class A { }

    class B : A { }

    static void Main(string[] args)
    {
        var attCount = typeof(B).GetCustomAttributes(true).Count();
        Console.WriteLine(attCount);
    }
}

Answer 1

Type.GetCustomAttributes()是一个扩展方法，它调用Attribute.GetCustomAttributes()，然后调用参数inherit设置为true的GetCustomAttributes。因此，默认情况下，在使用GetCustomAttributes()时，您已经在继承。

因此，唯一的区别是GetCustomAttributes()和GetCustomAttributes(inherit: false)。后者将禁用可继承属性的继承，而前者只会传递那些可继承的属性。

不能强制本身不可继承的属性是可继承的.

请参阅下面的示例以获得快速摘要：

void Main()
{
    typeof(A).GetCustomAttributes().Dump(); // both
    typeof(A).GetCustomAttributes(inherit: false).Dump(); // both

    typeof(B).GetCustomAttributes().Dump(); // inheritable
    typeof(B).GetCustomAttributes(inherit: false).Dump(); // none because inheritance is prevented

    typeof(C).GetCustomAttributes().Dump(); // both
    typeof(C).GetCustomAttributes(inherit: false).Dump(); // both because C comes with its own copies
}

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

[AttributeUsage(AttributeTargets.Class, Inherited = false)]
public class NonInheritableExampleAttribute : Attribute { }

[InheritableExample]
[NonInheritableExample]
public class A { }

public class B : A { }

[InheritableExample]
[NonInheritableExample]
public class C : A { }