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Shared Instance

Constructors should not be used to generate shared instances.

What does this mean ?

When a class is marked with Managed Extensibility Framework (MEF) PartCreationPolicy(CreationPolicy.Shared), a single, shared instance of the exported object is generated. As a result, utilizing the constructor to generate new instances makes no sense and will almost always result in unanticipated behavior.

What can happen ?

This rule causes a problem when a constructor of a class designated shared with a PartCreationPolicyAttribute is called.

Recommendation

You should make use of ServiceProvider.GetService(Type) returns the service object of the given type.

Sample Code

Vulnerable : 

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

public class Program
{
    public static void Main()
    {
        var fooBar = new FooBar(); // Noncompliant;
    }
}

Non Vulnerable : 

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

public class Program
{
    public static void Main()
    {
        var fooBar = serviceProvider.GetService<IFooBar>();
    }
}

References