Attribute Class

Reference

Definition

Namespace:: System

Assembly:: System.Runtime.dll

Assembly:: mscorlib.dll

Assembly:: netstandard.dll

Source:: Attribute.cs

Source:: Attribute.cs

Source:: Attribute.cs

Important

Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

Represents the base class for custom attributes.

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 Attribute
Implements _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: AttributeUsageAttribute ClassInterfaceAttribute SerializableAttribute ComVisibleAttribute

Implements: _Attribute

Examples

The following code example demonstrates the usage of Attribute.

using namespace System;
using namespace System::Reflection;

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

// A custom attribute to allow a target to have a pet.
public ref class AnimalTypeAttribute: public Attribute
{
public:

    // The constructor is called when the attribute is set.
    AnimalTypeAttribute( Animal pet )
    {
        thePet = pet;
    }


protected:

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

public:

    property Animal Pet 
    {
        // .. and show a copy to the outside world.
        Animal get()
        {
            return thePet;
        }

        void set( Animal value )
        {
            thePet = value;
        }
    }
};

// A test class where each method has its own pet.
ref class AnimalTypeTestClass
{
public:

    [AnimalType(Animal::Dog)]
    void DogMethod(){}


    [AnimalType(Animal::Cat)]
    void CatMethod(){}

    [AnimalType(Animal::Bird)]
    void BirdMethod(){}

};

int main()
{
    AnimalTypeTestClass^ testClass = gcnew AnimalTypeTestClass;
    Type^ type = testClass->GetType();

    // Iterate through all the methods of the class.
    System::Collections::IEnumerator^ myEnum = 
        type->GetMethods()->GetEnumerator();
    while ( myEnum->MoveNext() )
    {
        MethodInfo^ mInfo = safe_cast<MethodInfo^>(myEnum->Current);

        // Iterate through all the Attributes for each method.
        System::Collections::IEnumerator^ myEnum1 = 
            Attribute::GetCustomAttributes( mInfo )->GetEnumerator();
        while ( myEnum1->MoveNext() )
        {
            Attribute^ attr = safe_cast<Attribute^>(myEnum1->Current);

            // Check for the AnimalType attribute.
            if ( attr->GetType() == AnimalTypeAttribute::typeid )
                Console::WriteLine( "Method {0} has a pet {1} attribute.", 
                mInfo->Name, (dynamic_cast<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.
 */

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.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.

Remarks

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, .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 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 Attributes.

Constructors

Attribute()

Initializes a new instance of the Attribute class.

Properties

TypeId

When implemented in a derived class, gets a unique identifier for this Attribute.

Methods

Equals(Object)	Returns a value that indicates whether this instance is equal to a specified object.
GetCustomAttribute(Assembly, Type)	Retrieves a custom attribute applied to a specified assembly. Parameters specify the assembly and the type of the custom attribute to search for.
GetCustomAttribute(Assembly, Type, Boolean)	Retrieves a custom attribute applied to an assembly. Parameters specify the assembly, the type of the custom attribute to search for, and an ignored search option.
GetCustomAttribute(MemberInfo, Type)	Retrieves a custom attribute applied to a member of a type. Parameters specify the member, and the type of the custom attribute to search for.
GetCustomAttribute(MemberInfo, Type, Boolean)	Retrieves a custom attribute applied to a member of a type. Parameters specify the member, the type of the custom attribute to search for, and whether to search ancestors of the member.
GetCustomAttribute(Module, Type)	Retrieves a custom attribute applied to a module. Parameters specify the module, and the type of the custom attribute to search for.
GetCustomAttribute(Module, Type, Boolean)	Retrieves a custom attribute applied to a module. Parameters specify the module, the type of the custom attribute to search for, and an ignored search option.
GetCustomAttribute(ParameterInfo, Type)	Retrieves a custom attribute applied to a method parameter. Parameters specify the method parameter, and the type of the custom attribute to search for.
GetCustomAttribute(ParameterInfo, Type, Boolean)	Retrieves a custom attribute applied to a method parameter. Parameters specify the method parameter, the type of the custom attribute to search for, and whether to search ancestors of the method parameter.
GetCustomAttributes(Assembly)	Retrieves an array of the custom attributes applied to an assembly. A parameter specifies the assembly.
GetCustomAttributes(Assembly, Boolean)	Retrieves an array of the custom attributes applied to an assembly. Parameters specify the assembly, and an ignored search option.
GetCustomAttributes(Assembly, Type)	Retrieves an array of the custom attributes applied to an assembly. Parameters specify the assembly, and the type of the custom attribute to search for.
GetCustomAttributes(Assembly, Type, Boolean)	Retrieves an array of the custom attributes applied to an assembly. Parameters specify the assembly, the type of the custom attribute to search for, and an ignored search option.
GetCustomAttributes(MemberInfo)	Retrieves an array of the custom attributes applied to a member of a type. A parameter specifies the member.
GetCustomAttributes(MemberInfo, Boolean)	Retrieves an array of the custom attributes applied to a member of a type. Parameters specify the member, the type of the custom attribute to search for, and whether to search ancestors of the member.
GetCustomAttributes(MemberInfo, Type)	Retrieves an array of the custom attributes applied to a member of a type. Parameters specify the member, and the type of the custom attribute to search for.
GetCustomAttributes(MemberInfo, Type, Boolean)	Retrieves an array of the custom attributes applied to a member of a type. Parameters specify the member, the type of the custom attribute to search for, and whether to search ancestors of the member.
GetCustomAttributes(Module)	Retrieves an array of the custom attributes applied to a module. A parameter specifies the module.
GetCustomAttributes(Module, Boolean)	Retrieves an array of the custom attributes applied to a module. Parameters specify the module, and an ignored search option.
GetCustomAttributes(Module, Type)	Retrieves an array of the custom attributes applied to a module. Parameters specify the module, and the type of the custom attribute to search for.
GetCustomAttributes(Module, Type, Boolean)	Retrieves an array of the custom attributes applied to a module. Parameters specify the module, the type of the custom attribute to search for, and an ignored search option.
GetCustomAttributes(ParameterInfo)	Retrieves an array of the custom attributes applied to a method parameter. A parameter specifies the method parameter.
GetCustomAttributes(ParameterInfo, Boolean)	Retrieves an array of the custom attributes applied to a method parameter. Parameters specify the method parameter, and whether to search ancestors of the method parameter.
GetCustomAttributes(ParameterInfo, Type)	Retrieves an array of the custom attributes applied to a method parameter. Parameters specify the method parameter, and the type of the custom attribute to search for.
GetCustomAttributes(ParameterInfo, Type, Boolean)	Retrieves an array of the custom attributes applied to a method parameter. Parameters specify the method parameter, the type of the custom attribute to search for, and whether to search ancestors of the method parameter.
GetHashCode()	Returns the hash code for this instance.
GetType()	Gets the Type of the current instance. (Inherited from Object)
IsDefaultAttribute()	When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class.
IsDefined(Assembly, Type)	Determines whether any custom attributes are applied to an assembly. Parameters specify the assembly, and the type of the custom attribute to search for.
IsDefined(Assembly, Type, Boolean)	Determines whether any custom attributes are applied to an assembly. Parameters specify the assembly, the type of the custom attribute to search for, and an ignored search option.
IsDefined(MemberInfo, Type)	Determines whether any custom attributes are applied to a member of a type. Parameters specify the member, and the type of the custom attribute to search for.
IsDefined(MemberInfo, Type, Boolean)	Determines whether any custom attributes are applied to a member of a type. Parameters specify the member, the type of the custom attribute to search for, and whether to search ancestors of the member.
IsDefined(Module, Type)	Determines whether any custom attributes of a specified type are applied to a module. Parameters specify the module, and the type of the custom attribute to search for.
IsDefined(Module, Type, Boolean)	Determines whether any custom attributes are applied to a module. Parameters specify the module, the type of the custom attribute to search for, and an ignored search option.
IsDefined(ParameterInfo, Type)	Determines whether any custom attributes are applied to a method parameter. Parameters specify the method parameter, and the type of the custom attribute to search for.
IsDefined(ParameterInfo, Type, Boolean)	Determines whether any custom attributes are applied to a method parameter. Parameters specify the method parameter, the type of the custom attribute to search for, and whether to search ancestors of the method parameter.
Match(Object)	When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
ToString()	Returns a string that represents the current object. (Inherited from Object)

Explicit Interface Implementations

_Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr)	Maps a set of names to a corresponding set of dispatch identifiers.
_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)	Retrieves the type information for an object, which can be used to get the type information for an interface.
_Attribute.GetTypeInfoCount(UInt32)	Retrieves the number of type information interfaces that an object provides (either 0 or 1).
_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)	Provides access to properties and methods exposed by an object.

Applies to

Thread Safety

This type is thread safe.

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