Programming Visual Basic .NET, Second Edition

Chapter 18. Attributes and Reflection

Throughout this book, I have emphasized that a .NET application contains code, data, and metadata. Metadata is information about the data—that is, information about the types, code, assembly, and so forth—stored along with your program. This chapter explores how some of that metadata is created and used.

Attributes are a mechanism for adding metadata, such as compiler instructions and other data about your data, methods, and classes, to the program itself. Attributes are inserted into the metadata and are visible through ILDasm and other metadata-reading tools.

Reflection is the process by which a program can read its own metadata. A program is said to reflect on itself, extracting metadata from its assembly and using that metadata either to inform the user or to modify its own behavior.

Attributes

An attribute is an object that represents data you want to associate with an element in your program. The element to which you attach an attribute is referred to as the target of that attribute. For example, the attribute:

<NoIDispatch>

is associated with a class or an interface to indicate that the target class should derive from IUnknown rather than IDispatch when exporting to COM.

In Chapter 17, you saw this attribute:

<assembly: AssemblyKeyFile("c:\myStrongName.key")>

This inserts metadata into the assembly to designate the program’s StrongName.

Intrinsic Attributes

Attributes come in two flavors: intrinsic and custom. Intrinsic attributes ...