CA1402: Avoid overloads in COM visible interfaces

Cause

A Component Object Model (COM) visible interface declares overloaded methods.

Rule Description

When overloaded methods are exposed to COM clients, only the first method overload retains its name. Subsequent overloads are uniquely renamed by appending to the name an underscore character '_' and an integer that corresponds to the order of declaration of the overload. For example, consider the following methods.

void SomeMethod(int valueOne);
void SomeMethod(int valueOne, int valueTwo, int valueThree);
void SomeMethod(int valueOne, int valueTwo);

These methods are exposed to COM clients as the following.

void SomeMethod(int valueOne);
void SomeMethod_2(int valueOne, int valueTwo, int valueThree);
void SomeMethod_3(int valueOne, int valueTwo);

Visual Basic 6 COM clients cannot implement interface methods by using an underscore in the name.

How to Fix Violations

To fix a violation of this rule, rename the overloaded methods so that the names are unique. Alternatively, make the interface invisible to COM by changing the accessibility to internal (Friend in Visual Basic) or by applying the System.Runtime.InteropServices.ComVisibleAttribute attribute set to false.

When to Suppress Warnings

Do not suppress a warning from this rule.

Example

The following example shows an interface that violates the rule and an interface that satisfies the rule.

using System;
using System.Runtime.InteropServices;

[assembly: ComVisible(false)]
namespace InteroperabilityLibrary
{
   // This interface violates the rule.
   [ComVisible(true)]
   public interface IOverloadedInterface
   {
      void SomeMethod(int valueOne);
      void SomeMethod(int valueOne, int valueTwo);
   }

   // This interface satisfies the rule.
   [ComVisible(true)]
   public interface INotOverloadedInterface
   {
      void SomeMethod(int valueOne);
      void AnotherMethod(int valueOne, int valueTwo);
   }
}

Imports System
Imports System.Runtime.InteropServices

<Assembly: ComVisibleAttribute(False)>
Namespace InteroperabilityLibrary

   ' This interface violates the rule.
   <ComVisibleAttribute(True)> _ 
   Public Interface IOverloadedInterface

      Sub SomeSub(valueOne As Integer)
      Sub SomeSub(valueOne As Integer, valueTwo As Integer)

   End Interface

   ' This interface satisfies the rule.
   <ComVisibleAttribute(True)> _ 
   Public Interface INotOverloadedInterface

      Sub SomeSub(valueOne As Integer)
      Sub AnotherSub(valueOne As Integer, valueTwo As Integer)

   End Interface

End Namespace

Related Rules

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

CA1407: Avoid static members in COM visible types

CA1017: Mark assemblies with ComVisibleAttribute

See Also

Interoperating with Unmanaged Code Long Data Type