When should I use attribute in C#?

Question

I saw some of the examples of utilize attribute, e.g. (as a map for dynamic factory) http://msdn.microsoft.com/en-us/magazine/cc164170.aspx

Just wondering what is the advantage of using attribute? I can find the reference on http://msdn.microsoft.com/en-gb/z0w1kczw(VS.80).aspx however, I am not sure when and why should I try to use it.

Answer 1

In the .NET Framework, attributes can be used for many reasons -- like

• Defining which classes are serializable

• Choosing which methods are exposed in a Web service

Attributes allow us to add descriptions to classes, properties, and methods at design time that can then be examined at runtime via reflection.

Consider this example:

Say you have a class which has a method from older version which is still in use for any reason and now you have come up with a new version of the class which makes fantastic use of Generic List and LINQ and has a new method for similar purpose. You would like developers to prefer the new one provided in the later version of your library. How will you do that ? One way is to write in the documentation. A better way is to use attribute as follow.

public class AccountsManager {   [Obsolete("prefer GetAccountsList", true)]   static Account[] GetAccounts( ) { }       static List<Account> GetAccountsList( ) { }       } 

If an obsolete method is used when the program is compiled, the developer gets this info and decides accordingly.

AccountManager.GetAccounts() is obsolete: prefer GetAccountsList

We may also create and add Custom Attributes as per requirements.

Reference :

• Using Attributes in C#

---

Hope this helps

Answer 2

My recommendation: use attributes to state facts about mechanisms, but not to model aspects of your business domain.

More details:

https://docs.microsoft.com/en-us/archive/blogs/ericlippert/properties-vs-attributes