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AppDomain.DefineDynamicAssembly Method (AssemblyName, AssemblyBuilderAccess, String)

Defines a dynamic assembly using the specified name, access mode, and storage directory.

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

public AssemblyBuilder DefineDynamicAssembly (
	AssemblyName name,
	AssemblyBuilderAccess access,
	string dir
public final AssemblyBuilder DefineDynamicAssembly (
	AssemblyName name, 
	AssemblyBuilderAccess access, 
	String dir
public final function DefineDynamicAssembly (
	name : AssemblyName, 
	access : AssemblyBuilderAccess, 
	dir : String
) : AssemblyBuilder
Not applicable.



The unique identity of the dynamic assembly.


The mode in which the dynamic assembly will be accessed.


The name of the directory where the assembly will be saved. If dir is a null reference (Nothing in Visual Basic), the directory defaults to the current directory.

Return Value

Represents the dynamic assembly created.

Exception typeCondition


name is a null reference (Nothing in Visual Basic).


The Name property of name is a null reference (Nothing in Visual Basic).


The Name property of name begins with white space, or contains a forward or backward slash.


The operation is attempted on an unloaded application domain.

This method should only be used to define a dynamic assembly in the current application domain. For more information, see the Load(AssemblyName) method overload.


During the development of code that emits dynamic assemblies, it is recommended that you use an overload of the DefineDynamicAssembly method that specifies evidence and permissions, supply the evidence you want the dynamic assembly to have, and include SecurityPermissionFlag.SkipVerification in refusedPermissions. Including SkipVerification in the refusedPermissions parameter ensures that the MSIL is verified. A limitation of this technique is that it also causes SecurityException to be thrown when used with code that demands full trust.

The following sample demonstrates the DefineDynamicAssembly method and AssemblyResolve event.

For this code example to run, you must provide the fully qualified assembly name. For information about how to obtain the fully qualified assembly name, see Assembly Names.

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

class Test {
   public static void Main() {
      AppDomain currentDomain = AppDomain.CurrentDomain;

      InstantiateMyDynamicType(currentDomain);   // Failed!
      currentDomain.AssemblyResolve += new ResolveEventHandler(MyResolveEventHandler);
      InstantiateMyDynamicType(currentDomain);   // OK!

   static void InstantiateMyDynamicType(AppDomain domain) {
      try {
         // You must supply a valid fully qualified assembly name here. 
         domain.CreateInstance("Assembly text name, Version, Culture, PublicKeyToken", "MyDynamicType");
      } catch (Exception e) {

   static Assembly MyResolveEventHandler(object sender, ResolveEventArgs args) {
      return DefineDynamicAssembly((AppDomain) sender);
   static Assembly DefineDynamicAssembly(AppDomain domain) {
      // Build a dynamic assembly using Reflection Emit API.
      AssemblyName assemblyName = new AssemblyName();
      assemblyName.Name = "MyDynamicAssembly";

      AssemblyBuilder assemblyBuilder = domain.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run);
      ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule("MyDynamicModule");
      TypeBuilder typeBuilder = moduleBuilder.DefineType("MyDynamicType", TypeAttributes.Public);
      ConstructorBuilder constructorBuilder = typeBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.Standard, null);
      ILGenerator ilGenerator = constructorBuilder.GetILGenerator();
      ilGenerator.EmitWriteLine("MyDynamicType instantiated!");


      return assemblyBuilder;

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

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0