Articolo
11/18/2011

Attribute Class

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

Represents the base class for custom attributes.

Inheritance Hierarchy

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

Syntax

'Declaration
<ClassInterfaceAttribute(ClassInterfaceType.None)> _
<AttributeUsageAttribute(AttributeTargets.All, Inherited := True, AllowMultiple := False)> _
<ComVisibleAttribute(True)> _
Public MustInherit Class Attribute

[ClassInterfaceAttribute(ClassInterfaceType.None)]
[AttributeUsageAttribute(AttributeTargets.All, Inherited = true, AllowMultiple = false)]
[ComVisibleAttribute(true)]
public abstract class Attribute

The Attribute type exposes the following members.

Constructors

	Name	Description
	Attribute	Initializes a new instance of the Attribute class.

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Methods

	Name	Description
	Equals	Infrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Overrides Object.Equals(Object).)
	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.)
	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(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(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(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(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, 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, 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, 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(MemberInfo)	Retrieves an array of the custom attributes applied to a member of a type. A parameter specifies the member.
	GetCustomAttributes(Module)	Retrieves an array of the custom attributes applied to a module. A parameter specifies the module.
	GetCustomAttributes(ParameterInfo)	Retrieves an array of the custom attributes applied to a method parameter. A parameter specifies the method parameter.
	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(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(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(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(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, 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, 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, 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. (Overrides Object.GetHashCode().)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	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(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(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(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(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, 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, 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, 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	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.)

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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, 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.

Examples

The following code example demonstrates the usage of Attribute.

Note:
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control.

Imports System.Reflection

' 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

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

Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      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)
               outputBlock.Text += String.Format("Method {0} has a pet {1} attribute.", _
                    mInfo.Name(), attrCustom.Pet.ToString()) + vbCrLf
            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.

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 = Pet; }
   }
}

// 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 Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      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))
               outputBlock.Text += String.Format(
                   "Method {0} has a pet {1} attribute.",
                   mInfo.Name, ((AnimalTypeAttribute)attr).Pet) + "\n";
         }

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

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

This type is thread safe.

Inheritance Hierarchy

Condividi tramite

Attribute Class

Inheritance Hierarchy

Syntax

Constructors

Methods

Remarks

Examples

Version Information

Silverlight

Silverlight for Windows Phone

XNA Framework

Platforms

Thread Safety

See Also

Reference

Other Resources

Inheritance Hierarchy

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