An attribute is a powerful .NET language feature that is attached to a target programming element (e.g., a class, method, assembly, interface, etc.) to customize behaviors or extract organizational information of the target at design, compile, or runtime.
The paradigm of attributed programming first appeared in the Interface Definition Language (IDL) of COM interfaces. Microsoft extended the concept to Transaction Server (MTS) and used it heavily in COM+. It is a clean approach to associate metadata with program elements and later use the metadata at design, compile or run time to accomplish some common objectives. In .NET, Microsoft went a step further by allowing the implementation of attributes in the source code, unlike the implementation in MTS and COM+ where attributes were defined in a separate repository. To understand the power of attributes, consider the serialization of an object. In .NET, you just need to mark a class Serializable to make its member variables as Serializable.
For example:
using System;
using System.IO;
using System.Runtime.Serialization.Formatters.Soap;
[Serializable]
public class User{
public string userID;
public string password;
public string email;
public string city;
public void Save(string fileName){
FileStream s=new FileStream(fileName,FileMode.Create);
SoapFormatter sf=new SoapFormatter();
sf.Serialize(s,this);
}
static void Main(string[] args){
User u=new User();
u.userID="firstName";
u.password="Zxfd12Qs";
u.email="[email protected]";
u.city="TheCity";
u.Save("user.txt");
}
}
Note: You may have to Add a reference to assembly System.Runtime.Serialization.Formatters.Soap.dll
The above example illustrates the power of attributes. We do not have to tell what to serialize; we just need to mark the class as serializable by annotating the class with Serializable attribute. Of course, we need to tell the serialization format (as in the Save method).
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