Question

I am trying to instance a view model from my catalog

when I use Container.GetExportedValue and then initialise the properties all instances have their properties set to the value of the final value of ‘p’. but when I use a standard initialiser they are fine.

so in my example FormViewModel’s Name property in the MEF instancing example has these values

C
C
C

but in the normal instance example has these values

A
B
C

It is behaving like there is some shared reference between all instances coming from the MEF container.

      var worker = new BackgroundWorker();
        worker.DoWork += (o, ea) =>
                         {
                             _forms = new ObservableCollection<FormViewModel>(
                                 FormsExplorerRepository.GetForms()
                                     .Select(p =>
                                             {
 // This way of instancing does strange stuff 
                                                 var fvm = Container.GetExportedValue<FormViewModel>();

// This is fine but of course I'm not getting the importing constructor called
                                                 var fvm = new FormViewModel();

                                                 fvm.Workspace = this;
                                                 fvm.FormId = p.FormId;
                                                 fvm.Label = p.Label;
                                                 fvm.Name = p.Name;
                                                 fvm.Disclaimer = p.Disclaimer;
                                                 fvm.CertificationText = p.CertificationText;
                                                 fvm.Schemes = FormViewModelExtensions.InitialiseSchemes(p);
                                                 return fvm;
                                             })
                                     .ToList());
                         };

here are the view model’s constructors

    public FormViewModel()
        : base(null, true)
    {

    }

    [ImportingConstructor]
    public FormViewModel(
        IDialogManager dialogs,
        IEventAggregator events)
        : base(null, true)
    {
        _events = events;
        _events.Subscribe(this);

        _dialogs = dialogs;
    }

and I have an export attribute on the class definition

 [Export(typeof(FormViewModel)), PartCreationPolicy(CreationPolicy.NonShared)]
public class FormViewModel 

I hope there is enough info here for someone to help

Answer 1

I found my error

I wasn’t using the right syntax in my AddExportedValue (the one I commented out here was the wrong way)

(container, batch) =>
{
    // batch.AddExportedValue(new FormViewModel());
    batch.AddExportedValue<Func<FormViewModel>>container.GetExportedValue<FormViewModel>);
}