CA1413: Avoid non-public fields in COM visible value types







Breaking Change



A value type that is specifically marked as visible to Component Object Model (COM) declares a nonpublic instance field.

Rule Description

Nonpublic instance fields of COM-visible value types are visible to COM clients. Review the content of the field for information that should not be exposed, or that will have an unintended design or security effect.

By default, all public value types are visible to COM. However, to reduce false positives, this rule requires the COM visibility of the type to be explicitly stated. The containing assembly must be marked with the System.Runtime.InteropServices.ComVisibleAttribute set to false and the type must be marked with the ComVisibleAttribute set to true.

How to Fix Violations

To fix a violation of this rule and keep the field hidden, change the value type to a reference type or remove the ComVisibleAttribute attribute from the type.

When to Suppress Warnings

It is safe to suppress a warning from this rule if public exposure of the field is acceptable.


The following example shows a type that violates the rule.

Imports System
Imports System.Runtime.InteropServices

<Assembly: ComVisibleAttribute(False)>
Namespace InteroperabilityLibrary

   <ComVisibleAttribute(True)> _ 
   Public Structure SomeStructure

      Friend SomeInteger As Integer 

   End Structure 

End Namespace
using System;
using System.Runtime.InteropServices;

[assembly: ComVisible(false)]
namespace InteroperabilityLibrary
   public struct SomeStruct
      internal int SomeValue;

CA1407: Avoid static members in COM visible types

CA1017: Mark assemblies with ComVisibleAttribute

See Also


Qualifying .NET Types for Interoperation

Other Resources

Interoperating with Unmanaged Code