DefineDynamicAssembly Method (AssemblyName, AssemblyBuilderAccess, String, Evidence, PermissionSet, PermissionSet, PermissionSet)

AppDomain.DefineDynamicAssembly Method (AssemblyName, AssemblyBuilderAccess, String, Evidence, PermissionSet, PermissionSet, PermissionSet)

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

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

public AssemblyBuilder DefineDynamicAssembly (
	AssemblyName name,
	AssemblyBuilderAccess access,
	string dir,
	Evidence evidence,
	PermissionSet requiredPermissions,
	PermissionSet optionalPermissions,
	PermissionSet refusedPermissions
public final AssemblyBuilder DefineDynamicAssembly (
	AssemblyName name, 
	AssemblyBuilderAccess access, 
	String dir, 
	Evidence evidence, 
	PermissionSet requiredPermissions, 
	PermissionSet optionalPermissions, 
	PermissionSet refusedPermissions
public final function DefineDynamicAssembly (
	name : AssemblyName, 
	access : AssemblyBuilderAccess, 
	dir : String, 
	evidence : Evidence, 
	requiredPermissions : PermissionSet, 
	optionalPermissions : PermissionSet, 
	refusedPermissions : PermissionSet
) : 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.


The evidence supplied for the dynamic assembly. The evidence is used unaltered as the final set of evidence used for policy resolution.


The required permissions request.


The optional permissions request.


The refused permissions request.

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.

The permission requests specified for requiredPermissions, optionalPermissions, and refusedPermissions are used only if evidence is also supplied, or if the dynamic assembly is saved and reloaded into memory.


During the development of code that emits dynamic assemblies, it is recommended that you 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.

Only fully trusted callers can supply their evidence when defining a dynamic Assembly. The runtime will map the Evidence through the security policy to determine the granted permissions. Partially trusted callers must supply a null evidence. If evidence is a null reference (Nothing in Visual Basic), the runtime copies the permission sets, that is, the current grant and deny sets, from the caller's Assembly to the dynamic Assembly being defined and marks policy as resolved.

If the dynamic Assembly is saved to disk, subsequent loads will get grants based on policies associated with the location where the Assembly was saved.

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.


In the .NET Framework versions 1.0, 1.1, and 2.0, the declarative security attributes applied to a dynamic assembly by using the requiredPermissions, optionalPermissions, and refusedPermissions parameters are stored in the old XML metadata format. See Emitting Declarative Security Attributes.

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

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