FieldBuilder.SetCustomAttribute Method

Parameters

• customBuilder
  Type: System.Reflection.Emit.CustomAttributeBuilder
  An instance of a helper class to define the custom attribute.

Imports System.Reflection
Imports System.Reflection.Emit

<AttributeUsage(AttributeTargets.All, AllowMultiple:=False)> _
Public Class MyAttribute
    Inherits Attribute
    Private myStringValue As String

    Public ReadOnly Property MyString As String
        Get
            Return myStringValue 
        End Get
    End Property

    Public Sub New(ByVal myString As String)
        myStringValue = myString
    End Sub 
End Class 

Public Class Example

    Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

        ' Create a name for the assembly.
        Dim myAssemblyName As New AssemblyName("EmittedAssembly")
        ' Create the dynamic assembly in the current application domain.
        Dim myAssemblyBuilder As AssemblyBuilder = _
              AppDomain.CurrentDomain.DefineDynamicAssembly(myAssemblyName, _
                    AssemblyBuilderAccess.Run)
        Dim myModuleBuilder As ModuleBuilder = _
              myAssemblyBuilder.DefineDynamicModule("EmittedModule")
        ' Define a public class named 'CustomClass' in the assembly.
        Dim myTypeBuilder As TypeBuilder = myModuleBuilder.DefineType("CustomClass", _
                                               TypeAttributes.Public)

        ' Define a private String field named 'MyField' in the type.
        Dim myFieldBuilder As FieldBuilder = myTypeBuilder.DefineField("MyField", _
                                       GetType(String), FieldAttributes.Public)

        ' To set a custom attribute, first get the constructor for the attribute.
        ' Use the constructor and an array of arguments for the constructor to
        ' create a CustomAttributeBuilder. Finally, use the CustomAttributeBuilder
        ' to set the attribute on the enumeration. 
        Dim myAttributeType As Type = GetType(MyAttribute)
        Dim myConstructorInfo As ConstructorInfo = _
                     myAttributeType.GetConstructor(New Type() {GetType(String)})
        Dim attributeBuilder As _
            New CustomAttributeBuilder(myConstructorInfo, New Object() {"Test"})
        myFieldBuilder.SetCustomAttribute(attributeBuilder)

         Try
        Dim myCustomClass As Type = myTypeBuilder.CreateType()

        ' Retrieve the values of Attributes applied to field and display them.
        Dim myFieldInfo As FieldInfo = myCustomClass.GetField("MyField")
        For Each attr As Object In myFieldInfo.GetCustomAttributes(True)

            outputBlock.Text &= attr.ToString() & vbCrLf
            If TypeOf attr Is MyAttribute Then
                outputBlock.Text &= String.Format("    MyString: {0}" & vbCrLf, _
                    CType(attr, MyAttribute).MyString.ToString())
            End If
        Next
         Catch e As Exception
            outputBlock.Text &= "Exception Caught " + e.Message & vbCrLf
        End Try
    End Sub 
End Class 

' This example produces output similar to the following:
'
'SilverlightApplication.MyAttribute
'    MyString: Test

using System;
using System.Reflection;
using System.Reflection.Emit;

[AttributeUsage(AttributeTargets.All, AllowMultiple = false)]
public class MyAttribute : Attribute
{
    private string myStringValue;

    public string MyString { get { return myStringValue; }}   

    public MyAttribute(string myString)
    {
        myStringValue = myString;
    }
}

class Example
{
    public static void Demo(System.Windows.Controls.TextBlock outputBlock)
    {
        // Create a simple name for the assembly.
        AssemblyName myAssemblyName = new AssemblyName("EmittedAssembly");
        // Create the dynamic assembly.
        AssemblyBuilder myAssemblyBuilder =
            AppDomain.CurrentDomain.DefineDynamicAssembly(
                myAssemblyName, AssemblyBuilderAccess.Run);
        ModuleBuilder myModuleBuilder =
                 myAssemblyBuilder.DefineDynamicModule("EmittedModule");
        // Define a public class named 'CustomClass' in the assembly.
        TypeBuilder myTypeBuilder = myModuleBuilder.DefineType("CustomClass",
            TypeAttributes.Public);

        // Define a private String field named 'MyField' in the type.
        FieldBuilder myFieldBuilder =
            myTypeBuilder.DefineField("MyField", typeof(String), FieldAttributes.Public);

        // To set a custom attribute, first get the constructor for the attribute.
        // Use the constructor and an array of arguments for the constructor to
        // create a CustomAttributeBuilder. Finally, use the CustomAttributeBuilder
        // to set the attribute on the enumeration. 
        Type myAttributeType = typeof(MyAttribute);
        ConstructorInfo myConstructorInfo = 
            myAttributeType.GetConstructor(new Type[] { typeof(string) });
        CustomAttributeBuilder attributeBuilder =
            new CustomAttributeBuilder(myConstructorInfo, new object[] { "Test" });
        myFieldBuilder.SetCustomAttribute(attributeBuilder);

        Type myCustomClass = myTypeBuilder.CreateType();
        // Retrieve the values of Attributes applied to field and display to console.
        FieldInfo myFieldInfo = myCustomClass.GetField("MyField");
        foreach (object attr in myFieldInfo.GetCustomAttributes(true))
        {
            outputBlock.Text += attr.ToString() + "\n";
            if (attr is MyAttribute)
            {
                outputBlock.Text += String.Format("    MyString: {0}\n",
                    ((MyAttribute) attr).MyString.ToString());
            }
        }
    }
}

/* This example produces output similar to the following:

MyAttribute
    MyString: Test
 */