您需要进行几项更改，才能使用内置版本的System.ComponentModel.Composition编译和运行此示例。

class Program
{
    [ImportMany] // [Import]
    public IEnumerable<string> Messages { get; set; }

    [ImportMany] // [Import]
    public IEnumerable<IOutputString> OutputSet { get; set; }

    [Import("OutputMessages")]
    public Action<IEnumerable<IOutputString>, IEnumerable<string>> OutputMessages { get; set; }

    public void Run()
    {

        var catalog = new AggregateCatalog(); // AggregatingComposablePartCatalog
        catalog.Catalogs.Add(new DirectoryCatalog(@"..\..\..\ExternalMessages\bin\Debug")); // DirectoryPartCatalog
        catalog.Catalogs.Add(new DirectoryCatalog(@"..\..\..\ExtraMessages")); // DirectoryPartCatalog
        catalog.Catalogs.Add(new AssemblyCatalog(Assembly.GetExecutingAssembly())); // AttributedAssemblyPartCatalog
        var container = new CompositionContainer(catalog); // CompositionContainer(catalog.CreateResolver());

        // container.AddPart(this);
        // container.Compose();
        container.ComposeParts(this);

        OutputMessages(OutputSet, Messages);

    }

    static void Main(string[] args)
    {
        Program p = new Program();
        p.Run();
    }
}

目录零件目录现在称为DirectoryCatalog

我想，你是在寻找DirectoryCatalog