Articolo
11/18/2011

AttributeUsageAttribute Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Specifies the usage of another attribute class. This class cannot be inherited.

Inheritance Hierarchy

System.Object
System.Attribute
System.AttributeUsageAttribute

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
<AttributeUsageAttribute(AttributeTargets.Class, Inherited := True)> _
<ComVisibleAttribute(True)> _
Public NotInheritable Class AttributeUsageAttribute _
    Inherits Attribute

[AttributeUsageAttribute(AttributeTargets.Class, Inherited = true)]
[ComVisibleAttribute(true)]
public sealed class AttributeUsageAttribute : Attribute

The AttributeUsageAttribute type exposes the following members.

Constructors

	Name	Description
	AttributeUsageAttribute	Initializes a new instance of the AttributeUsageAttribute class with the specified list of AttributeTargets, the AllowMultiple value, and the Inherited value.

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Properties

	Name	Description
	AllowMultiple	Gets or sets a Boolean value indicating whether more than one instance of the indicated attribute can be specified for a single program element.
	Inherited	Gets or sets a Boolean value indicating whether the indicated attribute can be inherited by derived classes and overriding members.
	ValidOn	Gets a set of values identifying which program elements that the indicated attribute can be applied to.

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Methods

	Name	Description
	Equals	Infrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Returns the hash code for this instance. (Inherited from Attribute.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	Match	When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	ToString	Returns a string that represents the current object. (Inherited from Object.)

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Remarks

When you are defining your own attribute class, you can control the manner in which it is used by placing an AttributeUsageAttribute on your attribute class. The indicated attribute class must derive from Attribute, either directly or indirectly.

Attribute classes have positional and named parameters. Each public constructor for an attribute class defines a valid sequence of positional parameters for that class. Named parameters are defined by the non-static, public, and read-write fields or properties of the attribute class.

The three properties of AttributeUsageAttribute are set by defining the following parameters:

ValidOn

This positional parameter specifies the program elements that the indicated attribute can be placed on. The set of all possible elements that you can place an attribute on is listed in the AttributeTargets enumeration. You can combine several AttributeTargets values using a bitwise OR operation to get the desired combination of valid program elements.

AllowMultiple

This named parameter specifies whether the indicated attribute can be specified more than once for a given program element.

Inherited

This named parameter specifies whether the indicated attribute can be inherited by derived classes and overriding members.

For more information about using attributes, see Attribute and Accessing Custom Attributes.

Examples

The definition of the DispId attribute illustrates the use of a bitwise OR operation to combine several AttributeTargets values.

Imports System
<AttributeUsage(AttributeTargets.Method _
Or AttributeTargets.Field _
Or AttributeTargets.Property)> _
Public Class DispIdAttribute
Inherits System.Attribute

Public Sub New(ByVal value As Integer)
 ' . . .
End Sub

Public ReadOnly Property Value() As Integer
 Get
    ' . . .
    Return 0
 End Get
End Property
End Class

[AttributeUsage(AttributeTargets.Method | AttributeTargets.Field |
AttributeTargets.Property)]
public class DispIdAttribute : System.Attribute
{
  public DispIdAttribute(int value)
  {
     // . . .
  }

  public int Value
  {
     get
     {
        // . . .
        return 0;
     }
  }
}

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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