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ExtensibleClassFactory Class

Enables customization of managed objects that extend from unmanaged objects during creation.

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

public sealed class ExtensibleClassFactory

The ExtensibleClassFactory allows users to specify a delegate that is called during construction of a runtime callable wrapper (RCW) that provides an instance of the underlying COM object. In effect, the callback acts as the class factory for the COM object wrapped by the RCW. Without the callback, the common language runtime creates the underlying COM object by calling CoCreateInstance. This callback provides an alternative way of activating the underlying object, such as with a COM moniker or by providing a singleton object. The RegisterObjectCreationCallback method must be called in the static initializer of the class that is extending the RCW. Only one object creation callback is permitted per object type. When the extensible RCW is activated, the callback is registered. When the underlying COM object needs to be created, the callback is called to provide a reference to the object. The callback must return an IUnknown interface pointer for the base object.

Registers a delegate that will be called whenever an instance of a managed type that extends from an unmanaged type needs to allocate the aggregated unmanaged object. This delegate is expected to allocate and aggregate the unmanaged object and is called in place of a CoCreateInstance. This routine must be called in the context of the static initializer for the class for which the callbacks will be made.

using System;
using System.Runtime.InteropServices;

public class CallBack
   public IntPtr Activate(IntPtr Aggregator)
      ECFSRV32Lib.ObjectActivator oCOM = new ECFSRV32Lib.ObjectActivator();
      ECFSRV32Lib.IObjectActivator itf = (ECFSRV32Lib.IObjectActivator)oCOM;
      return (IntPtr) itf.CreateBaseComponent((int)Aggregator);

// The EcfInner class. First .NET class derived directly from COM class. 
public class EcfInner : ECFSRV32Lib.BaseComponent
   static CallBack callbackInner;

   static void RegisterInner()
      callbackInner = new CallBack();
      System.Runtime.InteropServices.ExtensibleClassFactory.RegisterObjectCreationCallback(new System.Runtime.InteropServices.ObjectCreationDelegate(callbackInner.Activate));

   //This is the static initializer.     
   static EcfInner()


Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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

.NET Framework

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