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

Applies to: Visual Studio Visual Studio for Mac

Cause

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.

Example

The following example shows a type that violates the rule.

using System;
using System.Runtime.InteropServices;

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

Imports System
Imports System.Runtime.InteropServices

<Assembly: ComVisibleAttribute(False)>
Namespace InteroperabilityLibrary

   <ComVisibleAttribute(True)> _ 
   Public Structure SomeStructure

      Friend SomeInteger As Integer

   End Structure

End Namespace

Related rules

CA1407: Avoid static members in COM visible types

CA1017: Mark assemblies with ComVisibleAttribute

See also

• Interoperating with Unmanaged Code
• Qualifying .NET Types for Interoperation