MEF problem with import - wpf

Question

I have problem with import shell-view-model to view-model class, I use MEF.
Shell-view-model :
namespace Spirit.ViewModels
{
using Caliburn.Micro;
using System.ComponentModel.Composition;
public interface IShellViewModel
{
void ShowLogOnView();
void ShowMessengerView();
}
[Export(typeof(IShellViewModel))]
public class ShellViewModel : Conductor<IScreen>, IShellViewModel
{
public ShellViewModel()
{
ShowLogOnView();
}
public void ShowLogOnView()
{
ActivateItem(new LogOnViewModel());
}
public void ShowMessengerView()
{
ActivateItem(new LogOnViewModel());
}
}
}
I need this class import in view-model class:
[Export]
public class LogOnViewModel : Screen, IDataErrorInfo
{
[Import]
private IShellViewModel _shellViewModel;
public void LogOn(string nick, string password)
{
IMessengerViewModel vm = IoC.Get<MessengerViewModel>();
_shellViewModel.ShowMessengerView();
}
}
Problem is after initialize is variable _shellViewModel null.
My bootstraper look like this:
public class MefBootStrapper : Bootstrapper<IShellViewModel>
{
}
MY SOLUTION:
I create interface assembly and refer this assembly in external service dll and also in wpf app.
In bootstraper I load this assembly with reflection:
var catalog =
new AggregateCatalog(
AssemblySource.Instance.Select(x => new AssemblyCatalog(x)).OfType<ComposablePartCatalog>());
catalog.Catalogs.Add(
new AssemblyCatalog(string.Format(
CultureInfo.InvariantCulture, "{0}{1}", System.IO.Directory.GetCurrentDirectory(), #"\Pokec_Toolkit.dll")));
_container = new CompositionContainer(catalog);
Than I create conductor class:
public interface IShellViewModel
{
void ShowLogOnView();
void ShowMessengerView();
}
[Export(typeof(IShellViewModel))]
public class ShellViewModel : Conductor<IScreen>, IShellViewModel
{
public ShellViewModel()
{
ShowLogOnView();
}
public void ShowLogOnView()
{
ActivateItem(IoC.Get<LogOnViewModel>());
}
public void ShowMessengerView()
{
ActivateItem(IoC.Get<MessengerViewModel>());
}
}
And in view-model I have this:
[Export]
public class LogOnViewModel : Screen, IDataErrorInfo, ILogOnViewModel
{
[Import]
private IShellViewModel _shellViewModel;
[Import]
private IPokecConnection _pokecConn;
//this method is bind on event click of button
public void LogOn(string nick, string password)
{
//SHOW NEW WIEW
_shellViewModel.ShowMessengerView();
}
}