There is no mystery really...
An attribute is actually an object that is associated with any of these elements: Assembly, Class, Method, Delegate, Enum, Event, Field, Interface, Property and Struct.
They can be used to associate declarative information and retrieve such information (at Runtime) by using reflection. In other words, you can use attributes to inject additional information to the assemblies that can be queried at Runtime if needed using reflection.
An attribute basically just comprises of its name and optionally, a list of parameters.
From MSDN Attributes (C#)
Attributes provide a powerful method of associating metadata, or
declarative information, with code (assemblies, types, methods,
properties, and so forth). After an attribute is associated with a
program entity, the attribute can be queried at run time by using a
technique called reflection. For more information, see Reflection
(C#).
Attributes have the following properties:
Attributes add metadata to your program. Metadata is information about the types defined in a program. All .NET assemblies contain a
specified set of metadata that describes the types and type members
defined in the assembly. You can add custom attributes to specify any
additional information that is required. For more information, see,
Creating Custom Attributes (C#).
You can apply one or more attributes to entire assemblies, modules, or smaller program elements such as classes and properties.
Attributes can accept arguments in the same way as methods and properties.
Your program can examine its own metadata or the metadata in other
programs by using reflection. For more information, see Accessing
Attributes by Using Reflection (C#).
If you want to receive information about the Metadata stored in an Attribute you need to do something like this
Exmaple
Lifted from How do I read an attribute on a class at runtime?
[DomainName("MyTable")]
Public class MyClass : DomainBase
{}
...
public static class AttributeExtensions
{
public static TValue GetAttributeValue<TAttribute, TValue>(
this Type type,
Func<TAttribute, TValue> valueSelector)
where TAttribute : Attribute
{
var att = type.GetCustomAttributes(
typeof(TAttribute), true
).FirstOrDefault() as TAttribute;
if (att != null)
{
return valueSelector(att);
}
return default(TValue);
}
}
and use like this:
string name = typeof(MyClass).GetAttributeValue((DomainNameAttribute dna) => dna.Name);
