Attribute Class

Definition

public ref class Attribute abstract

public ref class Attribute abstract : System::Runtime::InteropServices::_Attribute

[System.AttributeUsage(System.AttributeTargets.All, AllowMultiple=false, Inherited=true)]public abstract class Attribute

[System.AttributeUsage(System.AttributeTargets.All, AllowMultiple=false, Inherited=true)][System.Runtime.InteropServices.ClassInterface(System.Runtime.InteropServices.ClassInterfaceType.None)][System.Serializable]public abstract class Attribute : System.Runtime.InteropServices._Attribute

[System.AttributeUsage(System.AttributeTargets.All, AllowMultiple=false, Inherited=true)][System.Runtime.InteropServices.ClassInterface(System.Runtime.InteropServices.ClassInterfaceType.None)][System.Serializable][System.Runtime.InteropServices.ComVisible(true)]public abstract class Attribute : System.Runtime.InteropServices._Attribute

[<System.AttributeUsage(System.AttributeTargets.All, AllowMultiple=false, Inherited=true)>]type Attribute = class

[<System.AttributeUsage(System.AttributeTargets.All, AllowMultiple=false, Inherited=true)>][<System.Runtime.InteropServices.ClassInterface(System.Runtime.InteropServices.ClassInterfaceType.None)>][<System.Serializable>]type Attribute = class    interface _Attribute

[<System.AttributeUsage(System.AttributeTargets.All, AllowMultiple=false, Inherited=true)>][<System.Runtime.InteropServices.ClassInterface(System.Runtime.InteropServices.ClassInterfaceType.None)>][<System.Serializable>][<System.Runtime.InteropServices.ComVisible(true)>]type Attribute = class    interface _Attribute

Public MustInherit Class Attribute

Public MustInherit Class AttributeImplements _Attribute

Inheritance

Object

Attribute

Derived

Microsoft.Extensions.Compliance.Classification.DataClassificationAttribute

Microsoft.Extensions.Configuration.ConfigurationKeyNameAttribute

Microsoft.Extensions.Configuration.UserSecrets.UserSecretsIdAttribute

Microsoft.Extensions.DependencyInjection.ActivatorUtilitiesConstructorAttribute

Microsoft.Extensions.DependencyInjection.FromKeyedServicesAttribute

More…

Attributes

AttributeUsageAttributeClassInterfaceAttributeSerializableAttributeComVisibleAttribute

Implements

_Attribute

Examples

The following code example demonstrates the usage ofAttribute.

using System;using System.Reflection;// 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 class AnimalTypeAttribute : Attribute {    // The constructor is called when the attribute is set.    public AnimalTypeAttribute(Animal pet) {        thePet = pet;    }    // Keep a variable internally ...    protected Animal thePet;    // .. and show a copy to the outside world.    public Animal Pet {        get { return thePet; }        set { thePet = value; }    }}// A test class where each method has its own pet.class AnimalTypeTestClass {    [AnimalType(Animal.Dog)]    public void DogMethod() {}    [AnimalType(Animal.Cat)]    public void CatMethod() {}    [AnimalType(Animal.Bird)]    public void BirdMethod() {}}class DemoClass {    static void Main(string[] args) {        AnimalTypeTestClass testClass = new AnimalTypeTestClass();        Type type = testClass.GetType();        // Iterate through all the methods of the class.        foreach(MethodInfo mInfo in type.GetMethods()) {            // Iterate through all the Attributes for each method.            foreach (Attribute attr in                Attribute.GetCustomAttributes(mInfo)) {                // Check for the AnimalType attribute.                if (attr.GetType() == typeof(AnimalTypeAttribute))                    Console.WriteLine(                        "Method {0} has a pet {1} attribute.",                        mInfo.Name, ((AnimalTypeAttribute)attr).Pet);            }        }    }}/* * Output: * Method DogMethod has a pet Dog attribute. * Method CatMethod has a pet Cat attribute. * Method BirdMethod has a pet Bird attribute. */

open System// An enumeration of animals. Start at 1 (0 = uninitialized).type Animal =    | Dog = 1    | Cat = 2    | Bird = 3// A custom attribute to allow a target to have a pet.type AnimalTypeAttribute(pet) =    inherit Attribute()    member val Pet = pet with get, set// A test class where each method has its own pet.type AnimalTypeTestClass() =    [<AnimalType(Animal.Dog)>]    member _.DogMethod() = ()    [<AnimalType(Animal.Cat)>]    member _.CatMethod() = ()    [<AnimalType(Animal.Bird)>]    member _.BirdMethod() = ()let testClass = AnimalTypeTestClass()let clsType = testClass.GetType()// Iterate through all the methods of the class.for mInfo in clsType.GetMethods() do    // Iterate through all the Attributes for each method.    for attr in Attribute.GetCustomAttributes mInfo do        // Check for the AnimalType attribute.        if attr.GetType() = typeof<AnimalTypeAttribute> then            printfn $"Method {mInfo.Name} has a pet {(attr :?> AnimalTypeAttribute).Pet} attribute."// Output://   Method DogMethod has a pet Dog attribute.//   Method CatMethod has a pet Cat attribute.//   Method BirdMethod has a pet Bird attribute.

Imports System.ReflectionPublic 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 SubEnd Module' Output:' Method DogMethod has a pet Dog attribute.' Method CatMethod has a pet Cat attribute.' Method BirdMethod has a pet Bird attribute.

Remarks

TheAttribute 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, .NET 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 common type system.

All attribute types derive directly or indirectly from theAttribute 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 theAttributeTargets class to specify the target element to which the attribute is applied.

TheAttribute class provides convenient methods to retrieve and test custom attributes. For more information about using attributes, seeApplying Attributes andAttributes.

Thread Safety

This type is thread safe.

See also

• Applying Attributes
• Extending Metadata Using Attributes