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

Note: This API is now obsolete. The non-obsolete alternative is DefineDynamicAssembly(AssemblyName, AssemblyBuilderAccess, String).

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

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

[ObsoleteAttribute("Assembly level declarative security is obsolete and is no longer enforced by the CLR by default.  Please see for more information.")]
public AssemblyBuilder DefineDynamicAssembly(
	AssemblyName name,
	AssemblyBuilderAccess access,
	string dir,
	Evidence evidence,
	PermissionSet requiredPermissions,
	PermissionSet optionalPermissions,
	PermissionSet refusedPermissions


Type: System.Reflection.AssemblyName
The unique identity of the dynamic assembly.
Type: System.Reflection.Emit.AssemblyBuilderAccess
The mode in which the dynamic assembly will be accessed.
Type: System.String
The name of the directory where the assembly will be saved. If dir is null, the directory defaults to the current directory.
Type: System.Security.Policy.Evidence
The evidence supplied for the dynamic assembly. The evidence is used unaltered as the final set of evidence used for policy resolution.
Type: System.Security.PermissionSet
The required permissions request.
Type: System.Security.PermissionSet
The optional permissions request.
Type: System.Security.PermissionSet
The refused permissions request.

Return Value

Type: System.Reflection.Emit.AssemblyBuilder
A dynamic assembly with the specified name and features.


_AppDomain.DefineDynamicAssembly(AssemblyName, AssemblyBuilderAccess, String, Evidence, PermissionSet, PermissionSet, PermissionSet)


name is null.


The Name property of name is null.


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 null, 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;

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0
Obsolete (compiler warning) in 4

.NET Framework Client Profile

Supported in: 3.5 SP1
Obsolete (compiler warning) in 4

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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