MVVM light: Pass object from view to viewmodel
===

I 've recently started working with WPF using MVVM light and I have the following (simple scenario).

1-MainWindow contains a listbox of elements.

2-When one is selected and the button is clicked, I fire a command:
        
        ReservoirViewerCommand.Execute(null);

3-On the viewmodel class i instantiate the command and send a message with the selected object:

        ReservoirViewerCommand = new RelayCommand(OpenReservoir);
        private void OpenReservoir()
        {
            Messenger.Default.Send(new LaunchShowReservoirMessage(){Reservoir=SelectedReservoir});          
        }
where:
class LaunchShowReservoirMessage:MessageBase
    {
        public Reservoir Reservoir { get; set; }
    }

4-The mainview registers the message and opens a new child window:

         private void RegisterMessages() {
            Messenger.Default.Register<LaunchShowReservoirMessage>(this,OnLaunchShowReservoir);
        }

        public void OnLaunchShowReservoir(LaunchShowReservoirMessage msg) {
            var showReservoir = new ReservoirViewerView();
            showReservoir.Show(); 
        }

What I need is that the new ViewModel (ReservoirViewerViewModel) can somehow get hold of the passed object through the message so that I can then display the details of this object on the child window.

I did some step-by-step debugging and the ViewModel constructor seems never to be reached.
Thanks,
e.