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CA1412: Mark ComSource Interfaces as IDispatch

TypeName

MarkComSourceInterfacesAsIDispatch

CheckId

CA1412

Category

Microsoft.Interoperability

Breaking Change

Breaking

A type is marked with the ComSourceInterfacesAttribute attribute and at least one specified interface is not marked with the InterfaceTypeAttribute attribute set to the InterfaceIsDispatch value.

ComSourceInterfacesAttribute is used to identify the event interfaces that a class exposes to Component Object Model (COM) clients. These interfaces must be exposed as InterfaceIsIDispatch to enable Visual Basic 6 COM clients to receive event notifications. By default, if an interface is not marked with the InterfaceTypeAttribute attribute, it is exposed as a dual interface.

To fix a violation of this rule, add or modify the InterfaceTypeAttribute attribute so that its value is set to InterfaceIsIDispatch for all interfaces that are specified with the ComSourceInterfacesAttribute attribute.

Do not suppress a warning from this rule.

The following example shows a class where one of the interfaces violates the rule.

using System;
using System.Runtime.InteropServices;

[assembly: ComVisible(true)]
namespace InteroperabilityLibrary
{
   // This violates the rule for type EventSource.
   [InterfaceType(ComInterfaceType.InterfaceIsDual)]
   public interface IEventsInterface
   {
      void EventOne();
      void EventTwo();
   }

   // This satisfies the rule.
   [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
   public interface IMoreEventsInterface
   {
      void EventThree();
      void EventFour();
   }

   [ComSourceInterfaces(
      "InteroperabilityLibrary.IEventsInterface\0" + 
      "InteroperabilityLibrary.IMoreEventsInterface")]
   public class EventSource
   {
      // Event and method declarations.
   }
}
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