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FieldBuilder.SetCustomAttribute Method (ConstructorInfo, Byte[])

Sets a custom attribute using a specified custom attribute blob.

Namespace:  System.Reflection.Emit
Assembly:  mscorlib (in mscorlib.dll)

public void SetCustomAttribute(
	ConstructorInfo con,
	byte[] binaryAttribute


Type: System.Reflection.ConstructorInfo
The constructor for the custom attribute.
Type: System.Byte[]
A byte blob representing the attributes.


con or binaryAttribute is null.


The parent type of this field is complete.

See the metadata specification in the ECMA Partition II documentation for details on how to format binaryAttribute. The documentation is available online; see ECMA C# and Common Language Infrastructure Standards on MSDN and Standard ECMA-335 - Common Language Infrastructure (CLI) on the Ecma International Web site.

The following code sample illustrates the use of SetCustomAttribute in the context of FieldBuilder, using a byte blob.

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

namespace MySample
   [AttributeUsage(AttributeTargets.All, AllowMultiple = false)]
   public class MyAttribute1 :Attribute
      public string myCustomAttributeValue;
      public MyAttribute1(string myString)
         myCustomAttributeValue = myString;

   [AttributeUsage(AttributeTargets.All, AllowMultiple = false)]
   public class MyAttribute2 :Attribute
      public bool myCustomAttributeValue;
      public MyAttribute2(bool myBool)
         myCustomAttributeValue = myBool;


   class FieldBuilder_Sample
      private static Type CreateCallee(AppDomain currentDomain)

         // Create a simple name for the assembly.
         AssemblyName myAssemblyName = new AssemblyName();
         myAssemblyName.Name = "EmittedAssembly";
         // Create the called dynamic assembly.
         AssemblyBuilder myAssemblyBuilder =
            currentDomain.DefineDynamicAssembly(myAssemblyName, AssemblyBuilderAccess.RunAndSave);
         ModuleBuilder myModuleBuilder =
         // Define a public class named 'CustomClass' in the assembly.
         TypeBuilder myTypeBuilder = myModuleBuilder.DefineType("CustomClass",
         // Define a private String field named 'MyField' in the type.
         FieldBuilder myFieldBuilder =
            myTypeBuilder.DefineField("MyField", typeof(String), FieldAttributes.Public);
         Type myAttributeType1 = typeof(MyAttribute1);
         // Create a Constructorinfo object for attribute 'MyAttribute1'.
         ConstructorInfo myConstructorInfo = myAttributeType1.GetConstructor(
            new Type[1]{typeof(string)});
         // Create the CustomAttribute instance of attribute of type 'MyAttribute1'.
         CustomAttributeBuilder attributeBuilder =
                     new CustomAttributeBuilder( myConstructorInfo,new object[1]{"Test"});
         // Set the CustomAttribute 'MyAttribute1' to the Field.

          Type myAttributeType2 = typeof(MyAttribute2);
         // Create a Constructorinfo object for attribute 'MyAttribute2'.
        ConstructorInfo myConstructorInfo2 = myAttributeType2.GetConstructor(
            new Type[1]{typeof(bool)});
         // Set the CustomAttribute 'MyAttribute2' to the Field.
         myFieldBuilder.SetCustomAttribute(myConstructorInfo2,new byte[]{01,00,01,00,00});

         // Create a method.
         MethodBuilder myMethodBuilder= myTypeBuilder.DefineMethod("MyMethod",
            MethodAttributes.Public,null,new Type[2]{typeof(string),typeof(int)});

         ILGenerator myILGenerator = myMethodBuilder.GetILGenerator();
         myILGenerator.Emit(OpCodes.Stfld, myFieldBuilder);
         myILGenerator.EmitWriteLine("Value of the Field is :");

         return myTypeBuilder.CreateType();
      public static void Main()
            Type myCustomClass = CreateCallee(Thread.GetDomain());
            // Construct an instance of a type.
            Object myObject = Activator.CreateInstance(myCustomClass);
            Console.WriteLine( "FieldBuilder Sample");
            // Find a method in this type and call it on this object.
            MethodInfo myMethodInfo = myCustomClass.GetMethod("MyMethod");
            myMethodInfo.Invoke(myObject, new object[2]{"Sample string",3});
            // Retrieve the values of Attributes applied to field and display to console.
            FieldInfo[] myFieldInfo = myCustomClass.GetFields();
            for(int i =0;i<myFieldInfo.Length;i++)
               object[] attributes = myFieldInfo[i].GetCustomAttributes(true);
               for(int index=0; index < attributes.Length; index++)
                  if(attributes[index] is MyAttribute1)
                     MyAttribute1 myCustomAttribute = (MyAttribute1)attributes[index];
                     Console.WriteLine("Attribute Value of (MyAttribute1): "
                                       + myCustomAttribute.myCustomAttributeValue);
                  if(attributes[index] is MyAttribute2)
                     MyAttribute2 myCustomAttribute = (MyAttribute2)attributes[index];
                     Console.WriteLine("Attribute Value of (MyAttribute2): "
                                       + myCustomAttribute.myCustomAttributeValue);
         catch (Exception e)
            Console.WriteLine("Exception Caught "+e.Message);

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

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