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

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.ComponentModel.Composition;
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using GalaSoft.MvvmLight.Messaging;
using ProductApp.Common;

namespace ProductApp.Views
{
    [Export(typeof(IModule)), ExportMetadata(MetadataKeys.Name, ModuleID.AddProductWindowView)]
    public partial class AddProductWindow : ChildWindow, IModule, ICleanup
    {
        public AddProductWindow()
        {
            InitializeComponent();
            Messenger.Default.Register(this, MessageToken.AddProductWindowMessage, new Action<string>(OnAddProductWindowMessage));

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

        private void OnAddProductWindowMessage(string buttonName)
        {
            switch (buttonName)
            {
                case "OK":
                    DialogResult = true;
                    break;
                case "Cancel":
                    DialogResult = false;
                    break;
                default:
                    break;
            }
        }

        public void Cleanup()
        {
            // Remove its imported ViewModel in the Category Service
            // Cleanup() in released module will be called
            ModuleCatalogService.Instance.ReleaseModule((IModule)DataContext);

            DataContext = null;

            // Clean up messagers
            Messenger.Default.Unregister(this);
        }

        private void productName_TextChanged(object sender, TextChangedEventArgs e)
        {
            CheckForOKButton();
        }

        private void unitPrice_TextChanged(object sender, TextChangedEventArgs e)
        {
            CheckForOKButton();
        }

        private void unitPrice_GotFocus(object sender, RoutedEventArgs e)
        {
            unitPrice.Background = new SolidColorBrush(Colors.White);
        }

        private void CheckForOKButton()
        {
            OKButton.IsEnabled = !(string.IsNullOrWhiteSpace(productName.Text) ||
                                   string.IsNullOrWhiteSpace(unitPrice.Text));
        }
    }
}