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Attribute Class

Represents the base class for custom attributes.

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

'Declaration
<SerializableAttribute> _
<ComVisibleAttribute(True)> _
<AttributeUsageAttribute(AttributeTargets.All, Inherited:=True, AllowMultiple:=False)> _
<ClassInterfaceAttribute(ClassInterfaceType.None)> _
Public MustInherit Class Attribute
	Implements _Attribute
'Usage
Dim instance As Attribute

/** @attribute SerializableAttribute() */ 
/** @attribute ComVisibleAttribute(true) */ 
/** @attribute AttributeUsageAttribute(AttributeTargets.All, Inherited=true, AllowMultiple=false) */ 
/** @attribute ClassInterfaceAttribute(ClassInterfaceType.None) */ 
public abstract class Attribute implements _Attribute
SerializableAttribute 
ComVisibleAttribute(true) 
AttributeUsageAttribute(AttributeTargets.All, Inherited=true, AllowMultiple=false) 
ClassInterfaceAttribute(ClassInterfaceType.None) 
public abstract class Attribute implements _Attribute
Not applicable.

The Attribute class associates predefined system information or user-defined custom information with a target element. A target element can be an assembly, class, constructor, delegate, enum, event, field, interface, method, portable executable file module, parameter, property, return value, struct, or another attribute.

Information provided by an attribute is also known as metadata. Metadata can be examined at run time by your application to control how your program processes data, or before run time by external tools to control how your application itself is processed or maintained. For example, the .NET Framework predefines and uses attribute types to control run-time behavior, and some programming languages use attribute types to represent language features not directly supported by the .NET Framework common type system.

All attribute types derive directly or indirectly from the Attribute class. Attributes can be applied to any target element; multiple attributes can be applied to the same target element; and attributes can be inherited by an element derived from a target element. Use the AttributeTargets class to specify the target element to which the attribute is applied.

The Attribute class provides convenient methods to retrieve and test custom attributes. For more information about using attributes, see Applying Attributes and Extending Metadata Using Attributes.

The following code example demonstrates the usage of Attribute.

Imports System
Imports System.Reflection

Public Module CustomAttrVB

    ' An enumeration of animals. Start at 1 (0 = uninitialized).
    Public Enum Animal
        ' Pets
        Dog = 1
        Cat
        Bird
    End Enum

    ' Visual Basic requires the AttributeUsage be specified.
    ' A custom attribute to allow a target to have a pet.
    <AttributeUsage(AttributeTargets.Method)> _
    Public Class AnimalTypeAttribute
        Inherits Attribute

        ' The constructor is called when the attribute is set.
        Public Sub New(ByVal animal As Animal)
            Me.thePet = animal
        End Sub

        ' Keep a variable internally ...
        Protected thePet As Animal

        ' .. and show a copy to the outside world.
        Public Property Pet() As Animal
            Get
                Return thePet
            End Get
            Set(ByVal Value As Animal)
                thePet = Value
            End Set
        End Property

    End Class

    ' A test class where each method has its own pet.
    Class AnimalTypeTestClass

        <AnimalType(Animal.Dog)> _
        Public Sub DogMethod()
        End Sub

        <AnimalType(Animal.Cat)> _
        Public Sub CatMethod()
        End Sub

        <AnimalType(Animal.Bird)> _
        Public Sub BirdMethod()
        End Sub
    End Class

    ' The runtime test.
    Sub Main()
        Dim testClass As New AnimalTypeTestClass()
        Dim tcType As Type = testClass.GetType()
        Dim mInfo As MethodInfo
        ' Iterate through all the methods of the class.
        For Each mInfo In tcType.GetMethods()
            Dim attr As Attribute
            ' Iterate through all the attributes of the method.
            For Each attr In Attribute.GetCustomAttributes(mInfo)
                If TypeOf attr Is AnimalTypeAttribute Then
                    Dim attrCustom As AnimalTypeAttribute = _
                        CType(attr, AnimalTypeAttribute)
                    Console.WriteLine("Method {0} has a pet {1} attribute.", _
                         mInfo.Name(), attrCustom.Pet.ToString())
                End If
            Next
        Next
    End Sub
End Module

' Output:
' Method DogMethod has a pet Dog attribute.
' Method CatMethod has a pet Cat attribute.
' Method BirdMethod has a pet Bird attribute.


package CustomAttrJSL; 

import System.*;
import System.Reflection.*;
  
public class Animal
{
    protected int pet;
    public static final int dog = 1;
    public static final int cat = 2;
    public static final int bird = 3;

    public Animal()
    {
        pet = 0;
    } //Animal
    public Animal(int p)
    {
        pet = p;
    } //Animal
    public String getPet()
    {
        switch (pet) {
            case 1 :
                return "Dog";
            case 2 :
                return "Cat";
            case 3 :
                return "Bird";
            default :
                return null;
        }
    } //getPet
} //Animal
      
// A custom attribute to allow a target to have a pet.
/** @attribute System.AttributeUsageAttribute(AttributeTargets.Method)
 */
public class AnimalTypeAttribute extends Attribute
{
    public AnimalTypeAttribute() { }
    // The constructor is called when the attribute is set.
    public AnimalTypeAttribute(int pet)
    {
        thePet = new Animal(pet);
    } //AnimalTypeAttribute

    // Keep a variable internally...
    protected Animal thePet;

    //.. and show a copy to the outside world.
    /** @property 
     */
    public Animal get_Pet()
    {
        return thePet;
    } //get_Pet

    /** @property 
     */
    public void set_Pet(Animal value)
    {
        thePet = value;
    } //set_Pet
} //AnimalTypeAttribute
      
 // A test class where each method has its own pet.
class AnimalTypeTestClass
{
    /** @attribute AnimalType(Animal.dog)
     */
    public void DogMethod()
    {
    } //DogMethod

    /** @attribute AnimalType(Animal.cat)
     */
    public void CatMethod()
    {
    } //CatMethod

    /** @attribute AnimalType(Animal.bird)
     */
    public void BirdMethod()
    {
    } //BirdMethod
} //AnimalTypeTestClass
   
class DemoClass
{
    public static void main(String[] args)
    {
        AnimalTypeTestClass testClass = new AnimalTypeTestClass();
        Type type = testClass.GetType();
        // Iterate through all the methods of the class.
        for (int iCtr1 = 0; iCtr1 < type.GetMethods().length; iCtr1++) {
            MethodInfo mInfo = type.GetMethods()[iCtr1];
            // Iterate through all the Attributes for each method.
            for (int iCtr2 = 0; 
                iCtr2 < Attribute.GetCustomAttributes(mInfo).length; 
                iCtr2++) {
               
                Attribute attr = Attribute.GetCustomAttributes(mInfo)[iCtr2];
                // Check for the AnimalType attribute.
                if (attr.GetType().
                    Equals(AnimalTypeAttribute.class.ToType())) {                
                    Console.WriteLine("Method {0} has a pet {1} attribute.", 
                        mInfo.get_Name(), 
                        ((AnimalTypeAttribute)attr).get_Pet().getPet());
                }
            }
        }
    } //main
} //DemoClass 

/*
 Output:
 Method DogMethod has a pet Dog attribute.
 Method CatMethod has a pet Cat attribute.
 Method BirdMethod has a pet Bird attribute.
*/

import System;
import System.Reflection;
import CustomAttrJS;

package CustomAttrJS {
    // An enumeration of animals. Start at 1 (0 = uninitialized).
    public enum Animal {
        // Pets.
        Dog = 1,
        Cat,
        Bird,
    }

    // A custom attribute to allow a target to have a pet.
    public AttributeUsage(AttributeTargets.Method) class AnimalTypeAttribute 
        extends Attribute {
            
        // The constructor is called when the attribute is set.
        public function AnimalTypeAttribute(pet : Animal) {
            thePet = pet;
        }

        // Keep a variable internally ...
        protected var thePet : Animal;

        // .. and show a copy to the outside world.
        public function get Pet() : Animal {
                    return thePet; 
                }
        
                public function set Pet(pet : Animal) {
                    thePet = pet; 
                }
    }

    // A test class where each method has its own pet.
    class AnimalTypeTestClass {
        public AnimalTypeAttribute(Animal.Dog) 
                function DogMethod() {}

        public AnimalTypeAttribute(Animal.Cat)
        function CatMethod() {}

        public AnimalTypeAttribute(Animal.Bird)
        function BirdMethod() {}
    }
}



var testClass : AnimalTypeTestClass = new AnimalTypeTestClass();
var type : Type = testClass.GetType();
// Iterate through all the methods of the class.
var mInfo : MethodInfo[] = type.GetMethods();
for (var i : int = 0; i < mInfo.length; i++) {
    // Iterate through all the Attributes for each method.
    var attr : Attribute[] = Attribute.GetCustomAttributes(mInfo[i]);
    for (var j : int = 0; j < attr.length; j++) 
    {
        // Check for the AnimalType attribute.
        if (attr[j].GetType() == AnimalTypeAttribute)
            Console.WriteLine(
                "Method {0} has a pet {1} attribute.", 
                mInfo[i].Name, AnimalTypeAttribute(attr[j]).Pet);
    }

}


/*
 * Output:
 * Method BirdMethod has a pet Bird attribute.
 * Method CatMethod has a pet Cat attribute.
 * Method DogMethod has a pet Dog attribute.
 *
 */

This type is thread safe.

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0
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