creating-custom-attributes.md

title	Creating Custom Attributes (Visual Basic)
ms.custom
ms.date	07/20/2015
ms.prod	.net
ms.reviewer
ms.suite
ms.technology	devlang-visual-basic
ms.tgt_pltfrm
ms.topic	article
ms.assetid	5c9ef584-6c7c-496b-92a9-6e42f8d9ca28
caps.latest.revision	3
author	dotnet-bot
ms.author	dotnetcontent

Creating Custom Attributes (Visual Basic)

You can create your own custom attributes by defining an attribute class, a class that derives directly or indirectly from xref:System.Attribute, which makes identifying attribute definitions in metadata fast and easy. Suppose you want to tag types with the name of the programmer who wrote the type. You might define a custom Author attribute class:

<System.AttributeUsage(System.AttributeTargets.Class Or   
                       System.AttributeTargets.Struct)>   
Public Class Author  
    Inherits System.Attribute  
    Private name As String  
    Public version As Double  
    Sub New(ByVal authorName As String)  
        name = authorName  
        version = 1.0  
    End Sub  
End Class  

The class name is the attribute's name, Author. It is derived from System.Attribute, so it is a custom attribute class. The constructor's parameters are the custom attribute's positional parameters. In this example, name is a positional parameter. Any public read-write fields or properties are named parameters. In this case, version is the only named parameter. Note the use of the AttributeUsage attribute to make the Author attribute valid only on class and Structure declarations.

You could use this new attribute as follows:

<Author("P. Ackerman", Version:=1.1)>   
Class SampleClass  
    ' P. Ackerman's code goes here...  
End Class  

AttributeUsage has a named parameter, AllowMultiple, with which you can make a custom attribute single-use or multiuse. In the following code example, a multiuse attribute is created.

' multiuse attribute  
<System.AttributeUsage(System.AttributeTargets.Class Or   
                       System.AttributeTargets.Struct,   
                       AllowMultiple:=True)>   
Public Class Author  
    Inherits System.Attribute  

In the following code example, multiple attributes of the same type are applied to a class.

<Author("P. Ackerman", Version:=1.1),   
Author("R. Koch", Version:=1.2)>   
Class SampleClass  
    ' P. Ackerman's code goes here...  
    ' R. Koch's code goes here...  
End Class  

Note

If your attribute class contains a property, that property must be read-write.

See Also

xref:System.Reflection
Visual Basic Programming Guide
Writing Custom Attributes
Reflection (Visual Basic)
Attributes (Visual Basic)
Accessing Attributes by Using Reflection (Visual Basic)
AttributeUsage (Visual Basic)