<Export()>
Public Class MyAddin
    Public ReadOnly Property theData As String
        Get
            Return "The Data!"
        End Get
    End Property
End Class

Public Class MyProgam
    Private _MyAddin As MyAddin

    <Import()>
    Public Property MyAddinProperty As MyAddin
        Get
            Return _MyAddin
        End Get
        Set(ByVal value As MyAddin)
            _MyAddin = value
        End Set
    End Property

End Class



Sub Main()
    Dim catalog As AggregateCatalog = New AggregateCatalog()
    catalog.Catalogs.Add(New AssemblyCatalog(GetType(MyAddin).Assembly))
    Dim container As CompositionContainer = New CompositionContainer(catalog)
    Dim theProgam As MyProgam = New MyProgam()
    container.SatisfyImportsOnce(theProgam)
    Console.WriteLine(theProgam.MyAddinProperty.theData)
    Console.ReadLine()

    container.Dispose()

End Sub

[Export]
class MyAddin
{
    public String myData { get { return "The data!"; } }
}

class MyProgram
{
    [Import]
    public MyAddin myAddin { get; set; }
}


class Program
{
    static void Main(string[] args)
    {
        AggregateCatalog catalog = new AggregateCatalog();
        catalog.Catalogs.Add(new AssemblyCatalog(typeof(MyAddin).Assembly));
        CompositionContainer _container = new CompositionContainer(catalog);
        MyProgram myProgram = new MyProgram();
        _container.SatisfyImportsOnce(myProgram);
        Console.WriteLine(myProgram.myAddin.myData);
        Console.ReadLine();

        _container.Dispose();
    }
}