Visual Basic 2005 in a Nutshell, Third Edition

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Chapter 9Attributes

9

Attributes

Attributes are declarative tags that can be used to annotate types (classes, struc-

tures, etc.) or type members, thereby modifying their meaning or customizing

their behavior. The descriptive information provided by each attribute is stored as

metadata in the .NET assembly and can be extracted either at design time or at

runtime using a process called reflection.

Consider the following example that uses the

<WebMethod> attribute.

<WebMethod(Description:="Indicates number of visitors to a page")> _

Public Function PageHitCount(baseURL As String) As Integer

Ordinarily, public methods of a class can be invoked locally through an instance

of that class; they are not treated as members of a web service. The

<WebMethod>

attribute marks an ordinary class method so that it is callable over the Internet as

part of a web service. This

<WebMethod> attribute includes a single property,

Description, which provides the text that will appear on the page describing the

web service.

If attributes provide such important software features, why aren’t they simply

implemented as language elements? The answer is “flexibility.” Attributes are

stored as metadata in an assembly, rather than as part of its executable code. As

an item of metadata, the attribute describes the program ...