Simple MVVM Toolkit - loosing ViewModel when switching them

Question

I'm using MVVM Toolkit. In my ViewModels I'm keeping data which I'd like to save when switching ViewModel to another.

Responsible for switching ViewModels is ViewModelLocator:

http://simplemvvmtoolkit.codeplex.com/wikipage?title=Getting%20Started point 8.

ViewModelLocator everytime returns new ViewModel:

public class ViewModelLocator
{
    // Create ProductListViewModel on demand
    public ProductListViewModel ProductListViewModel
    {
        get
        {
            IProductServiceAgent serviceAgent = new MockProductServiceAgent();
            return new ProductListViewModel(serviceAgent);
        }
    }
}

I don't want to break MVVM rules. I was thinking about creating new objects like this:

public class ViewModelLocator
{
    private ProductListViewModel productListViewModel;

    // Create ProductListViewModel on demand
    public ProductListViewModel ProductListViewModel
    {
        get
        {
            IProductServiceAgent serviceAgent = new MockProductServiceAgent();
            if (productListViewModel == null)
                 productListViewModel = new ProductListViewModel(serviceAgent);
            return productListViewModel;
        }
    }
}

... or while switching ViewModel serialize ViewModel, when loading it back - deserialize...

What is the proper solution of this problem?

Shouldn't the data reside in the model? So when switching ViewModels you only have to make sure they access the same model file. This could be done by static access, a factory.. — SvenG, Oct 07 '11 at 10:35

score 1 · Answer 1 · answered Mar 28 '12 at 16:47

I will recommend you to use any type of IoC container for that (for example Unity)

public class ViewModelLocator
{
    public static UnityContainer Contaner { get; private set;}

    static ViewModelLocator()
    {
        Container = new UnityContainer();

        Container.RegisterType<ProductListViewModel>(new ContainerControlledLifetimeManager());
    }

    public ProductListViewModel ProductViewModel
    {
        get
        {
            return Container.Resolve<ProductListViewModel>();
        }
    }
}

I think in MVVM Light Toolkit you have SimpleIoc - lightweight implementation of IoC container.

A model would be useful also. The view model contains view state, the model contains model data. — Ritch Melton, Mar 28 '12 at 16:51

Simple MVVM Toolkit - loosing ViewModel when switching them

1 Answers1