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CA1405: COM visible type base types should be COM visible


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The latest version of this topic can be found at CA1405: COM visible type base types should be COM visible.

|Breaking Change|DependsOnFix|

A Component Object Model (COM) visible type derives from a type that is not COM visible.

When a COM visible type adds members in a new version, it must abide by strict guidelines to avoid breaking COM clients that bind to the current version. A type that is invisible to COM presumes it does not have to follow these COM versioning rules when it adds new members. However, if a COM visible type derives from the COM invisible type and exposes a class interface of ClassInterfaceType.AutoDual or AutoDispatch (the default), all public members of the base type (unless they are specifically marked as COM invisible, which would be redundant) are exposed to COM. If the base type adds new members in a subsequent version, any COM clients that bind to the class interface of the derived type might break. COM visible types should derive only from COM visible types to reduce the chance of breaking COM clients.

To fix a violation of this rule, make the base types COM visible or the derived type COM invisible.

Do not suppress a warning from this rule.

The following example shows a type that violates the rule.

using System;
using System.Runtime.InteropServices;

[assembly: ComVisible(false)]
namespace InteroperabilityLibrary
   public class BaseClass
      public void SomeMethod(int valueOne) {}

   // This class violates the rule.
   public class DerivedClass : BaseClass
      public void AnotherMethod(int valueOne, int valueTwo) {}

Introducing the Class Interface
Interoperating with Unmanaged Code