How do you check if an attribute has been defined on a class?

Using the Attribute.IsDefined method is an efficient and reliable way to check if a specific attribute has been applied to a class. This method leverages .NET's reflection capabilities to interrogate the metadata associated with a class at runtime. By invoking this method with the target class type and the type of the attribute you are checking for, you receive a boolean value indicating whether the attribute is present.

This approach simplifies the process and abstracts the complexity of directly examining the class metadata or using other methods, ensuring that you are interacting with the type system in a structured and type-safe manner. The method is also widely recognized for its clarity and ease of use within the development community.

The other options, while they may provide some insight or potential ways to gather information, are less effective for specifically determining attribute presence. Checking class metadata manually can be error-prone and cumbersome, while inspecting a class in the debugger, although useful for observing state, does not directly answer the question of attribute application in a programmatic way. The Reflection.GetAttribute method does not exist in standard .NET; the correct method to look for attributes is, in fact, the IsDefined method.