Querying About Attributes
We know how to define an attribute by deriving it from System.Attribute and how to attach it to a type or member. Now what? How can we use attributes in code? In other words, how can we query a type or member as to the attributes (and its parameters) that have been attached? -
To query a type or member about its attached attributes, we must use reflection. Reflection is an advanced topic that's covered in Chapter 16, "Querying Metadata with Reflection," so I'll discuss only enough about it here to illustrate what's needed to retrieve attribute information at run time. If you want to learn more about reflection, refer to Chapter 16.
Reflection is a feature that allows you to dynamically determine at run time the type characteristics for an application. For example, you can use the .NET Framework Reflection APIs to iterate through the metadata for an entire assembly and produce a list of all classes, types, and methods that have been defined for that assembly. Let's look at some examples of attributes and how they would be queried using reflection.