FieldBuilder.SetCustomAttribute Method

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
 */