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CustomAttributeNamedArgument Structure

Note: This structure is new in the .NET Framework version 2.0.

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
/** @attribute SerializableAttribute() */ 
/** @attribute ComVisibleAttribute(true) */ 
public final class CustomAttributeNamedArgument extends ValueType
JScript suports the use of structures, but not the declaration of new ones.

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 System.Attribute.GetCustomAttributes, System.Reflection.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.

Positional arguments are represented by the CustomAttributeTypedArgument structure.

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

The following code example defines a custom attribute with two constructors and one property. 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. 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.

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

// 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;

    // Constructors. The parameterless constructor (.ctor) calls
    // the constructor that specifies ExampleKind, and supplies the
    // default value.
    //
    public ExampleAttribute(ExampleKind initKind)
    {
        kindValue = initKind;
    }
    public ExampleAttribute() : this(ExampleKind.FirstKind) {}

    // Properties. The Note property must be read/write, so that it
    // can be used as a named parameter.
    //
    public ExampleKind Kind { get { return kindValue; }}
    public string Note    
    {
        get { return noteValue; }
        set { noteValue = value; }
    }
}

// The example attribute is applied to the test class.
//
[Example(ExampleKind.SecondKind, Note="This is a note on the class.")]
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 )
            {
                Console.WriteLine("         Type: {0} Value: {1}", 
                    cata.ArgumentType, cata.Value);
            }

            Console.WriteLine("      Named arguments:");
            foreach( CustomAttributeNamedArgument cana 
                in cad.NamedArguments )
            {
                CustomAttributeTypedArgument cata = cana.TypedValue;
                Console.WriteLine("         MemberInfo: {0}", 
                    cana.MemberInfo);
                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
   [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.
   [System.Runtime.CompilerServices.CompilationRelaxationsAttribute((Int32)8)]
      Constructor: Void .ctor(Int32)
      Constructor arguments:
         Type: System.Int32 Value: 8
      Named arguments:

Attributes for type: Test
   [ExampleAttribute((ExampleKind)1, Note = "This is a note on the class.")]
      Constructor: Void .ctor(ExampleKind)
      Constructor arguments:
         Type: ExampleKind Value: 1
      Named arguments:
         MemberInfo: System.String Note
         Type: System.String Value: This is a note on the class.

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:
*/

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0
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