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

TypeName

AvoidNonpublicFieldsInComVisibleValueTypes

CheckId

CA1413

Category

Microsoft.Interoperability

Breaking Change

Breaking

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

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.

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.

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.

using System;
using System.Runtime.InteropServices;

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