Attributes - Illustrated C# 2005 - page 497

class. The .NET class library defines a class called Type , which has several methods that you can
use to access this information.
To use these methods, you can start by creating an instance of the class you want to query
and calling the instance's GetType method, which returns an object of type Type . Every class has
the GetType method, because GetType is a member of type object , which is the base from which
every class is derived.

Using the IsDefined Method
You can use the IsDefined method of the Type object to determine whether a particular
attribute is applied to a particular class. When this method is called, it returns a bool value that
tells whether an attribute is defined on a particular program construct.
For example, the following code declares an attributed class called MyClass , and also acts
as its own attribute consumer, by accessing an attribute declared and applied in the program
itself. At the top of the code are declarations of the attribute MyAttribute and the class MyClass ,
to which it is applied. The code does the following:

￿Firs , Main creates an object of the class. It then retrieves a reference to the Type object by
using the GetType method, which it inherited from its base class, object .

￿ With the reference to the Type object, it can call the IsDefined method to find out

whether attribute MyAttribute is applied to this class.
-

The first parameter takes a Type object of the attribute you are checking for.

- The second parameter is of type bool and specifies whether to search the inheritance

tree of MyClass to find the attribute.

[AttributeUsage(AttributeTargets.Class)]
public sealed class MyAttributeAttribute : System.Attribute
{ ... }

[MyAttribute("Check it out", "2.4")]
class MyClass { }

class Program {
static void Main() {
MyClass mc = new MyClass(); // Create an instance of the class.
Type t = mc.GetType(); // Get the Type object from the instance.
bool ItIsDefined = // Check the Type for the attribute.
t.IsDefined(typeof(MyAttributeAttribute), false);

Console.WriteLine("MyAttribute is applied to type {0}", t.Name);
}
}