S4428 — "PartCreationPolicyAttribute" should be used with "ExportAttribute"

Why is this an issue?

To customize the default behavior for an export in the Managed Extensibility Framework (MEF), applying the PartCreationPolicyAttribute is necessary. For the PartCreationPolicyAttribute to be meaningful in the context of an export, the class must also be annotated with the ExportAttribute.

This rule raises an issue when a class is annotated with the PartCreationPolicyAttribute but not with the ExportAttribute.

How to fix it

Code examples

Noncompliant code example

using System.ComponentModel.Composition;

[PartCreationPolicy(CreationPolicy.Any)] // Noncompliant
public class FooBar : IFooBar { }

Compliant solution

using System.ComponentModel.Composition;

[Export(typeof(IFooBar))]
[PartCreationPolicy(CreationPolicy.Any)]
public class FooBar : IFooBar { }

Resources

Documentation

• Microsoft Learn - Managed Extensibility Framework (MEF)
• Microsoft Learn - Attributed programming model overview (MEF)
• Microsoft Learn - PartCreationPolicyAttribute Class
• Microsoft Learn - ExportAttribute Class
• Microsoft Learn - CreationPolicy Enum

Articles & blog posts

• Stefan Henneken - MEF Part 1 – Fundamentals, Imports and Exports
• Stefan Henneken - MEF Part 2 – Metadata and creation policies
• Stefan Henneken - MEF Part 3 – Life cycle management and monitoring