Migrate from Basic to MVVM and MEF Composable Patterns for a Silverlight Application - Part 3

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows;
using System.Windows.Controls;
using ProductRiaLib.Web.Services;
using ProductRiaLib.Web.Models;
using System.ComponentModel.Composition;
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Messaging;
using ProductApp.Common;

namespace ProductApp.Views
{
    [Export(typeof(IModule)), ExportMetadata(MetadataKeys.Name, ModuleID.ProductListView)]
    public partial class ProductList : UserControl, IModule, ICleanup
    {
        private ModuleCatalogService _catalogService = ModuleCatalogService.Instance;
        private ChildWindow _addProdScreen;

        public ProductList()
        {
            InitializeComponent();

            // Register the massage handler for loading child window
            Messenger.Default.Register(this, MessageToken.LoadAddProductViewMessage,
                                       new Action<string>(OnLoadAddProductViewMessage));

            if (!ViewModelBase.IsInDesignModeStatic)
            {
                // Set the DataContext to the imported ViewModel
                DataContext = ModuleCatalogService.Instance.GetModule(ModuleID.ProductListViewModel);
            }
        }

        private void OnLoadAddProductViewMessage(string message)
        {
            // Load AddProductWindowView lazy module
            _addProdScreen = _catalogService.GetModuleLazy(ModuleID.AddProductWindowView) as ChildWindow;
            _addProdScreen.Show();
        }

        public void Cleanup()
        {
            if (_addProdScreen != null)
            {
                // Call Cleanup() in the child window if opened                
                ((ICleanup)_addProdScreen).Cleanup();

                // Remove the child window View Lazy module from Catelog Service
                ModuleCatalogService.Instance.ReleaseModuleLazy((IModule)_addProdScreen);

                _addProdScreen = null;
            }

            if (DataContext != null)
            {
                // Remove its imported ViewModel in the Category Service
                // The context.Dispose() will also call Cleanup() in released module
                // refrenced from MVVM Light ViewModelBase
                ModuleCatalogService.Instance.ReleaseModule((IModule)DataContext);

                DataContext = null;
            }

            // Clean up any messages this class registered
            Messenger.Default.Unregister(this);
        }
    }
}