CustomAttributeTypedArgument Struct

Definition

public value class CustomAttributeTypedArgument

public value class CustomAttributeTypedArgument : IEquatable<System::Reflection::CustomAttributeTypedArgument>

public struct CustomAttributeTypedArgument

public readonly struct CustomAttributeTypedArgument : IEquatable<System.Reflection.CustomAttributeTypedArgument>

public readonly struct CustomAttributeTypedArgument

[System.Runtime.InteropServices.ComVisible(true)]
[System.Serializable]
public struct CustomAttributeTypedArgument

type CustomAttributeTypedArgument = struct

[<System.Runtime.InteropServices.ComVisible(true)>]
[<System.Serializable>]
type CustomAttributeTypedArgument = struct

Public Structure CustomAttributeTypedArgument

Public Structure CustomAttributeTypedArgument
Implements IEquatable(Of CustomAttributeTypedArgument)

Inheritance

Object

ValueType

CustomAttributeTypedArgument

Attributes

ComVisibleAttribute SerializableAttribute

Implements

IEquatable<CustomAttributeTypedArgument>

Examples

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 the custom attributes.

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:
*/

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:

Remarks

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 the type and value of a positional argument specified for a custom attribute instance, without executing the attribute constructor. It also provides access to the type and value of a named argument without executing the code of the corresponding property of the custom attribute type.

The types and values of all the positional and named arguments of an attribute instance are provided by CustomAttributeTypedArgument structures. The positional attributes returned by the CustomAttributeData.ConstructorArguments property are directly represented by CustomAttributeTypedArgument structures, but the named arguments returned by the CustomAttributeData.NamedArguments property are represented by CustomAttributeNamedArgument structures; to get the CustomAttributeTypedArgument structure for a named argument, use the CustomAttributeNamedArgument.TypedValue property.

If an argument is an array of values, the Value property of the CustomAttributeTypedArgument that represents the argument returns a generic ReadOnlyCollection<T> of CustomAttributeTypedArgument objects. Each CustomAttributeTypedArgument object in the collection represents the corresponding element of the array.

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

See also

• CustomAttributeData
• CustomAttributeNamedArgument
• ReflectionOnlyLoad