ClassInterfaceAttribute Class
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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 sealed class ClassInterfaceAttribute : Attribute


Initializes a new instance of the ClassInterfaceAttribute class with the specified ClassInterfaceType enumeration member.


Initializes a new instance of the ClassInterfaceAttribute class with the specified ClassInterfaceType enumeration value.


When implemented in a derived class, gets a unique identifier for this Attribute.(Inherited from Attribute.)


Gets the ClassInterfaceType value that describes which type of interface should be generated for the class.


This API supports the product infrastructure and is not intended to be used directly from your code. Returns a value that indicates whether this instance is equal to a specified object.(Inherited from Attribute.)


Returns the hash code for this instance.(Inherited from Attribute.)


Gets the Type of the current instance.(Inherited from Object.)


When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class.(Inherited from Attribute.)


When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.(Inherited from Attribute.)


Returns a string that represents the current object.(Inherited from Object.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr)

Maps a set of names to a corresponding set of dispatch identifiers.(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)

Retrieves the type information for an object, which can be used to get the type information for an interface.(Inherited from Attribute.)


Retrieves the number of type information interfaces that an object provides (either 0 or 1).(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)

Provides access to properties and methods exposed by an object.(Inherited from 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 Tlbimp.exe (Type Library Importer) 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 System.Runtime.InteropServices;

public class MyClass
   public MyClass() {}

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1

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

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