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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)

'Declaration
<SerializableAttribute> _
<ComVisibleAttribute(True)> _
Public Structure CustomAttributeNamedArgument
'Usage
Dim instance As CustomAttributeNamedArgument

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 Note:

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.

Imports System
Imports System.Reflection
Imports System.Collections.Generic
Imports 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
End Enum 

' An example attribute. The attribute can be applied to all 
' targets, from assemblies to parameters. 
'
<AttributeUsage(AttributeTargets.All)> _
Public Class ExampleAttribute
    Inherits Attribute

    ' Data for properties. 
    Private kindValue As ExampleKind
    Private noteValue As String 
    Private arrayStrings() As String 
    Private arrayNumbers() As Integer 

    ' Constructors. The parameterless constructor (.ctor) calls 
    ' the constructor that specifies ExampleKind and an array of 
    ' strings, and supplies the default values. 
    
    Public Sub New(ByVal initKind As ExampleKind, ByVal initStrings() As String)
        kindValue = initKind
        arrayStrings = initStrings
    End Sub 
    Public Sub New(ByVal initKind As ExampleKind)
        Me.New(initKind, Nothing)
    End Sub 
    Public Sub New()
        Me.New(ExampleKind.FirstKind, Nothing)
    End Sub 

    ' Properties. The Note and Numbers properties must be read/write, so they  
    ' can be used as named parameters. 
    
    Public ReadOnly Property Kind As ExampleKind
        Get 
            Return kindValue 
        End Get 
    End Property 
    Public ReadOnly Property Strings As String()
        Get 
            Return arrayStrings 
        End Get 
    End Property 
    Public Property Note As String 
        Get 
            Return noteValue 
        End Get 
        Set
            noteValue = value
        End Set 
    End Property 
    Public Property Numbers As Integer()
        Get 
            Return arrayNumbers 
        End Get 
        Set
            arrayNumbers = value
        End Set 
    End Property 
End Class 

' 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 Integer() { 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 Sub TestMethod(<Example()> ByVal arg As Object)
    End Sub 

    ' Sub 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 Shared Sub Main()
        Dim asm As [Assembly] = Assembly.ReflectionOnlyLoad("source")
        Dim t As Type = asm.GetType("Test")
        Dim m As MethodInfo = t.GetMethod("TestMethod")
        Dim p() As ParameterInfo = m.GetParameters()

        Console.WriteLine(vbCrLf & "Attributes for assembly: '{0}'", asm)
        ShowAttributeData(CustomAttributeData.GetCustomAttributes(asm))
        Console.WriteLine(vbCrLf & "Attributes for type: '{0}'", t)
        ShowAttributeData(CustomAttributeData.GetCustomAttributes(t))
        Console.WriteLine(vbCrLf & "Attributes for member: '{0}'", m)
        ShowAttributeData(CustomAttributeData.GetCustomAttributes(m))
        Console.WriteLine(vbCrLf & "Attributes for parameter: '{0}'", p)
        ShowAttributeData(CustomAttributeData.GetCustomAttributes(p(0)))
    End Sub 

    Private Shared Sub ShowAttributeData( _
        ByVal attributes As IList(Of CustomAttributeData))

        For Each cad As CustomAttributeData _
            In CType(attributes, IEnumerable(Of CustomAttributeData))

            Console.WriteLine("   {0}", cad)
            Console.WriteLine("      Constructor: '{0}'", cad.Constructor)

            Console.WriteLine("      Constructor arguments:")
            For Each cata As CustomAttributeTypedArgument _
                In CType(cad.ConstructorArguments, IEnumerable(Of CustomAttributeTypedArgument))

                ShowValueOrArray(cata)
            Next

            Console.WriteLine("      Named arguments:")
            For Each cana As CustomAttributeNamedArgument _
                In CType(cad.NamedArguments, IEnumerable(Of CustomAttributeNamedArgument))

                Console.WriteLine("         MemberInfo: '{0}'", _
                    cana.MemberInfo)
                ShowValueOrArray(cana.TypedValue)
            Next 
        Next 
    End Sub 

    Private Shared Sub ShowValueOrArray(ByVal cata As CustomAttributeTypedArgument)
        If cata.Value.GetType() Is GetType(ReadOnlyCollection(Of CustomAttributeTypedArgument)) Then
            Console.WriteLine("         Array of '{0}':", cata.ArgumentType)

            For Each cataElement As CustomAttributeTypedArgument In cata.Value
                Console.WriteLine("             Type: '{0}'  Value: '{1}'", _
                    cataElement.ArgumentType, cataElement.Value)
            Next 
        Else
            Console.WriteLine("         Type: '{0}'  Value: '{1}'", _
                cata.ArgumentType, cata.Value)
        End If        
    End Sub 
End Class 

' 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:

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 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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

.NET Framework

Supported in: 3.5, 3.0, 2.0
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