ClassInterfaceAttribute Class

Indicates the type of class interface to be generated for a class exposed to COM, if an interface is generated at all.

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

[AttributeUsageAttribute(AttributeTargets::Assembly|AttributeTargets::Class, Inherited=false)] 
public ref class ClassInterfaceAttribute sealed : public Attribute
/** @attribute ComVisibleAttribute(true) */ 
/** @attribute AttributeUsageAttribute(AttributeTargets.Assembly|AttributeTargets.Class, Inherited=false) */ 
public final class ClassInterfaceAttribute extends Attribute
AttributeUsageAttribute(AttributeTargets.Assembly|AttributeTargets.Class, Inherited=false) 
public final class ClassInterfaceAttribute extends Attribute

You can apply this attribute to assemblies or classes.

This attribute controls whether the Type Library Exporter (Tlbexp.exe) automatically generates a class interface for the attributed class. A class interface carries the same name as the class itself, but the name is prefixed with an underscore. When exposed, the class interface contains all the public, non- static members of the managed class, including members inherited from its base class. Managed classes cannot access a class interface and have no need to as they can access the class members directly. Tlbexp.exe generates a unique interface identifier (IID) for the class interface.

Class interfaces can be dual or dispatch-only interfaces. Optionally, you can suppress the generation of the class interface and provide a custom interface instead. You expose or suppress a class interface by specifying a System.Runtime.InteropServices.ClassInterfaceType enumeration member. When you apply ClassInterfaceAttribute to an assembly, the attribute pertains to all classes in the assembly unless the individual classes override the setting with their own attribute.

Although class interfaces eliminate the task of explicitly defining interfaces for each class, their use in production applications is strongly discouraged. Dual class interfaces allow clients to bind to a specific interface layout that is subject to change as the class evolves. For example, consider a managed class that exposes a class interface to COM clients. The first version of the class contains methods North and South. An unmanaged client can bind to the class interface, which provides North as the first method in the class interface and method South as the second method. Now consider the next version of the class, which has a new method, East, inserted between methods North and South. Unmanaged clients that try to bind to the new class through the old class interface end up calling method East when they intend to call method South, because the positioning of methods within the interface has changed. Moreover, any change to the layout of a base class also affects the layout of the class interface for all derived classes. Managed clients, which bind directly to classes, do not exhibit the same versioning problems. For specific guidelines on using a class interface, see Introducing the Class Interface.

The Type Library Importer (Tlbimp.exe) always applies to imported classes the ClassInterfaceType.None enumeration member to indicate that existing COM classes never expose managed interfaces.

The following example shows how to apply the ClassInterfaceAttribute with the ClassInterfaceType value AutoDispatch, which generates an IDispatch interface for MyClass.

using namespace System::Runtime::InteropServices;

public ref class MyClass


import System.Runtime.InteropServices.*;

/** @attribute ClassInterface(ClassInterfaceType.AutoDispatch)
public class MyClass
    public MyClass()
    } //MyClass
} //MyClass 


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 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0