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CustomAttributeNamedArgument Structure

Represents a named argument of a custom attribute in the reflection-only context.

Namespace:  System.Reflection
Assembly:  mscorlib (in mscorlib.dll)
[SerializableAttribute]
[ComVisibleAttribute(true)]
public struct CustomAttributeNamedArgument

The CustomAttributeNamedArgument type exposes the following members.

  NameDescription
Public methodCustomAttributeNamedArgument(MemberInfo, Object)Initializes a new instance of the CustomAttributeNamedArgument class, which represents the specified field or property of the custom attribute, and specifies the value of the field or property.
Public methodCustomAttributeNamedArgument(MemberInfo, CustomAttributeTypedArgument)Initializes a new instance of the CustomAttributeNamedArgument class, which represents the specified field or property of the custom attribute, and specifies a CustomAttributeTypedArgument object that describes the type and value of the field or property.
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  NameDescription
Public propertySupported in .NET for Windows Store appsIsFieldGets a value that indicates whether the named argument is a field.
Public propertyMemberInfoGets the attribute member that would be used to set the named argument.
Public propertySupported in .NET for Windows Store appsMemberNameGets the name of the attribute member that would be used to set the named argument.
Public propertySupported in .NET for Windows Store appsTypedValueGets a CustomAttributeTypedArgument structure that can be used to obtain the type and value of the current named argument.
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  NameDescription
Public methodEqualsReturns a value that indicates whether this instance is equal to a specified object. (Overrides ValueType.Equals(Object).)
Public methodGetHashCodeReturns the hash code for this instance. (Overrides ValueType.GetHashCode().)
Public methodSupported in .NET for Windows Store appsGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodToStringReturns a string that consists of the argument name, the equal sign, and a string representation of the argument value. (Overrides ValueType.ToString().)
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  NameDescription
Public operatorStatic memberEqualityTests whether two CustomAttributeNamedArgument structures are equivalent.
Public operatorStatic memberInequalityTests whether two CustomAttributeNamedArgument structures are different.
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Code that is being examined in the reflection-only context cannot be executed, so it is not always possible to examine custom attributes by creating instances of them and then examining their properties, using methods like Attribute.GetCustomAttributes, MemberInfo.GetCustomAttributes, and so on. If the code for the attribute type itself is loaded into the reflection-only context, it cannot be executed.

The CustomAttributeNamedArgument structure is used by the CustomAttributeData class to provide access to a named argument specified for a custom attribute instance, without executing the code of the corresponding property of the custom attribute type. The TypedValue property returns a CustomAttributeTypedArgument structure that contains the type and value of the named argument.

Important noteImportant

Whether an argument is named or positional, you must access its type and value by using the CustomAttributeTypedArgument structure.

To create instances of the CustomAttributeData class, use the static GetCustomAttributes factory method.

The following example defines a custom attribute with four constructors and four properties. Two of the properties are read-only, and are set by using the positional parameters of the constructors. The other two properties are read/write, and can be set only by using named arguments. One positional property is an array of strings, and one named property is an array of integers.

The attribute is applied to the assembly, to a type declared in the assembly, to a method of the type, and to a parameter of the method. Different constructors are used for these cases. When executed, the assembly loads itself into the reflection-only context and displays information about the custom attributes that were applied to it and to the type and members it contains.

The attribute that is applied to the type demonstrates array properties, with both positional and named arguments.

using System;
using System.Reflection;
using System.Collections.Generic;
using System.Collections.ObjectModel;

// The example attribute is applied to the assembly.
[assembly:Example(ExampleKind.ThirdKind, Note="This is a note on the assembly.")]

// An enumeration used by the ExampleAttribute class. 
public enum ExampleKind
{
    FirstKind, 
    SecondKind, 
    ThirdKind, 
    FourthKind
};

// An example attribute. The attribute can be applied to all 
// targets, from assemblies to parameters. 
//
[AttributeUsage(AttributeTargets.All)]
public class ExampleAttribute : Attribute
{
    // Data for properties. 
    private ExampleKind kindValue;
    private string noteValue;
    private string[] arrayStrings;
    private int[] arrayNumbers;

    // Constructors. The parameterless constructor (.ctor) calls 
    // the constructor that specifies ExampleKind and an array of  
    // strings, and supplies the default values. 
    // 
    public ExampleAttribute(ExampleKind initKind, string[] initStrings)
    {
        kindValue = initKind;
        arrayStrings = initStrings;
    }
    public ExampleAttribute(ExampleKind initKind) : this(initKind, null) {}
    public ExampleAttribute() : this(ExampleKind.FirstKind, null) {}

    // Properties. The Note and Numbers properties must be read/write, so they 
    // can be used as named parameters. 
    // 
    public ExampleKind Kind { get { return kindValue; }}
    public string[] Strings { get { return arrayStrings; }}
    public string Note    
    {
        get { return noteValue; }
        set { noteValue = value; }
    }
    public int[] Numbers
    {
        get { return arrayNumbers; }
        set { arrayNumbers = value; }
    }
}

// The example attribute is applied to the test class. 
//
[Example(ExampleKind.SecondKind, 
         new string[] { "String array argument, line 1", 
                        "String array argument, line 2", 
                        "String array argument, line 3" }, 
         Note="This is a note on the class.",
         Numbers = new int[] { 53, 57, 59 })] 
public class Test
{
    // The example attribute is applied to a method, using the 
    // parameterless constructor and supplying a named argument. 
    // The attribute is also applied to the method parameter. 
    //
    [Example(Note="This is a note on a method.")]
    public void TestMethod([Example] object arg) { }

    // Main() gets objects representing the assembly, the test 
    // type, the test method, and the method parameter. Custom 
    // attribute data is displayed for each of these. 
    // 
    public static void Main()
    {
        Assembly asm = Assembly.ReflectionOnlyLoad("Source");
        Type t = asm.GetType("Test");
        MethodInfo m = t.GetMethod("TestMethod");
        ParameterInfo[] p = m.GetParameters();

        Console.WriteLine("\r\nAttributes for assembly: '{0}'", asm);
        ShowAttributeData(CustomAttributeData.GetCustomAttributes(asm));
        Console.WriteLine("\r\nAttributes for type: '{0}'", t);
        ShowAttributeData(CustomAttributeData.GetCustomAttributes(t));
        Console.WriteLine("\r\nAttributes for member: '{0}'", m);
        ShowAttributeData(CustomAttributeData.GetCustomAttributes(m));
        Console.WriteLine("\r\nAttributes for parameter: '{0}'", p);
        ShowAttributeData(CustomAttributeData.GetCustomAttributes(p[0]));
    }

    private static void ShowAttributeData(
        IList<CustomAttributeData> attributes)
    {
        foreach( CustomAttributeData cad in attributes )
        {
            Console.WriteLine("   {0}", cad);
            Console.WriteLine("      Constructor: '{0}'", cad.Constructor);

            Console.WriteLine("      Constructor arguments:");
            foreach( CustomAttributeTypedArgument cata 
                in cad.ConstructorArguments )
            {
                ShowValueOrArray(cata);
            }

            Console.WriteLine("      Named arguments:");
            foreach( CustomAttributeNamedArgument cana 
                in cad.NamedArguments )
            {
                Console.WriteLine("         MemberInfo: '{0}'", 
                    cana.MemberInfo);
                ShowValueOrArray(cana.TypedValue);
            }
        }
    }

    private static void ShowValueOrArray(CustomAttributeTypedArgument cata)
    {
        if (cata.Value.GetType() == typeof(ReadOnlyCollection<CustomAttributeTypedArgument>))
        {
            Console.WriteLine("         Array of '{0}':", cata.ArgumentType);

            foreach (CustomAttributeTypedArgument cataElement in 
                (ReadOnlyCollection<CustomAttributeTypedArgument>) cata.Value)
            {
                Console.WriteLine("             Type: '{0}'  Value: '{1}'",
                    cataElement.ArgumentType, cataElement.Value);
            }
        }
        else
        {
            Console.WriteLine("         Type: '{0}'  Value: '{1}'", 
                cata.ArgumentType, cata.Value);
        }
    }
}

/* This code example produces output similar to the following:

Attributes for assembly: 'source, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'
   [System.Runtime.CompilerServices.CompilationRelaxationsAttribute((Int32)8)]
      Constructor: 'Void .ctor(Int32)'
      Constructor arguments:
         Type: 'System.Int32'  Value: '8'
      Named arguments:
   [System.Runtime.CompilerServices.RuntimeCompatibilityAttribute(WrapNonExceptionThrows = True)]
      Constructor: 'Void .ctor()'
      Constructor arguments:
      Named arguments:
         MemberInfo: 'Boolean WrapNonExceptionThrows'
         Type: 'System.Boolean'  Value: 'True'
   [ExampleAttribute((ExampleKind)2, Note = "This is a note on the assembly.")]
      Constructor: 'Void .ctor(ExampleKind)'
      Constructor arguments:
         Type: 'ExampleKind'  Value: '2'
      Named arguments:
         MemberInfo: 'System.String Note'
         Type: 'System.String'  Value: 'This is a note on the assembly.'

Attributes for type: 'Test'
   [ExampleAttribute((ExampleKind)1, new String[3] { "String array argument, line 1", "String array argument, line 2", "String array argument, line 3" }, Note = "This is a note on the class.", Numbers = new Int32[3] { 53, 57, 59 })]
      Constructor: 'Void .ctor(ExampleKind, System.String[])'
      Constructor arguments:
         Type: 'ExampleKind'  Value: '1'
         Array of 'System.String[]':
             Type: 'System.String'  Value: 'String array argument, line 1'
             Type: 'System.String'  Value: 'String array argument, line 2'
             Type: 'System.String'  Value: 'String array argument, line 3'
      Named arguments:
         MemberInfo: 'System.String Note'
         Type: 'System.String'  Value: 'This is a note on the class.'
         MemberInfo: 'Int32[] Numbers'
         Array of 'System.Int32[]':
             Type: 'System.Int32'  Value: '53'
             Type: 'System.Int32'  Value: '57'
             Type: 'System.Int32'  Value: '59'

Attributes for member: 'Void TestMethod(System.Object)'
   [ExampleAttribute(Note = "This is a note on a method.")]
      Constructor: 'Void .ctor()'
      Constructor arguments:
      Named arguments:
         MemberInfo: 'System.String Note'
         Type: 'System.String'  Value: 'This is a note on a method.'

Attributes for parameter: 'System.Object arg'
   [ExampleAttribute()]
      Constructor: 'Void .ctor()'
      Constructor arguments:
      Named arguments:
*/

.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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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