When should I use attribute in C#?

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AccountManager.GetAccounts() is obsolete: prefer GetAccountsList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#

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Hope this helps

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

Attributes are appropriate when you want to attach metadata to your classes or class members, as well as when applying a common behaviour without having to implement a certain interface for each unit that shares the behaviour. The latter is an example of aspect-oriented programming.