Inheritance of C# attribute classes

Question

How does inheritance of attribute classes work in C#? To clarify, I am talking about the inheritance of the attribute classes themselves (i.e. base classes of System.Attributes), NOT any classes that happen to have them as attribute.

For some reason, I cannot seem to find anything on this (my searches always turn up with the other meaning).

For example, if a have a class AttributeA which extends System.Attribute:

Do I have to separately mark subclasses of AttributeA with [AttributeUsage()]. (Since System.AttributeUsage's inheritance is true, I don't think I will.)
Will AllowMultiple=false on the AttributeUsage of AttributeA prevent me from having multiple subclasses of AttributeA for attributes?

EDIT:

Programmers can only read code.

[AttributeUsage(AttributeTargets.Class, AllowMultiple=false)]
class AttributeA
{ }

class AttributeB : AttributeA
{ }

class AttributeC : AttributeA
{ }

[AttributeB]
[AttributeC]
class Foo
{ }

Does this work?

It seems to me that both of these could be checked by trying it... — Marc Gravell
– Marc Gravell, Commented Apr 19, 2013 at 22:45
Yes, I am not able to do that right now...and I wanted to save someone else some time on this too. Even I could just find the relevant documentation, I would be happy... — Paul Draper
– Paul Draper, Commented Apr 19, 2013 at 22:47

Paul Draper · Accepted Answer · 2013-04-19 23:09:28Z

1

(I was finally able to try it.)

The example code does compile. I still like to have documentation, although I suppose C# is C# and it isn't going to change that. (Right?)

Evidently:

The subclasses inherit AttributeUsage, as expected.
AllowMultiple refers only to attributes of (strictly) the original class, not subclasses.
Also, AttributeUsage can be effectively "re-defined".

With

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

[AttributeUsage(AttributeTargets.Class, AllowMultiple = true)]
class AttributeB : AttributeA
{ }

class AttributeC : AttributeA
{ }

the following is okay

[AttributeA]
[AttributeB]
[AttributeB]
[AttributeC]
class Foo
{ }

but this isn't

[AttributeA]
[AttributeB]
[AttributeC]
[AttributeC]
class Foo
{ }

answered Apr 19, 2013 at 23:09

Paul Draper

84.2k53 gold badges216 silver badges303 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Christopher von Blum · Accepted Answer · 2014-08-24 16:29:58Z

1

You can control this behavior by using the named parameter Inherited for your AttributeUsageAttribute.

[AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = false)]
class AttributeA
{ }

class AttributeB : AttributeA
{ }

class AttributeC : AttributeA
{ }

edited Aug 24, 2014 at 16:29

answered Jul 19, 2014 at 21:01

Christopher von Blum

9010 bronze badges

Comments

Flavia · Accepted Answer · 2013-04-19 22:50:14Z

0

The attribute usage is for the classes using the attributes.

For example, if you mark class A with AttributeA and class B is a subclass of A, you don't need to mark class B with AttributeB if AttributeA AttributeUsage's inheritance is true.

answered Apr 19, 2013 at 22:50

Flavia

5614 silver badges9 bronze badges

4 Comments

Paul Draper Over a year ago

You miss the question. I am asking about marking A with AttributeA AND subclass AttributeB.

Flavia Over a year ago

[AttributeUsageAttribute(AttributeTargets.Class, Inherited=true)] public sealed class AttributeUsageAttribute : Attribute. So it looks like it is inheritable.

Paul Draper Over a year ago

And it that allowed if AllowMultiple=false?

Flavia Over a year ago

If it is inheritable it should inherit everything

Collectives™ on Stack Overflow

Inheritance of C# attribute classes

3 Answers 3

Comments

Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related