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