Introduction to Composite WPF (CAL, Prism): Part 2

using JamSoft.CALDemo.Modules.PageManager.Core;
using Microsoft.Practices.Composite.Events;
using Microsoft.Practices.Composite.Regions;
using Microsoft.Practices.Composite.Wpf.Events;
using Microsoft.Practices.Unity;

namespace JamSoft.CALDemo.Modules.PageManager
{
    public class MainRegionController : IMainRegionController
    {
        private readonly IUnityContainer _container;
        private readonly IRegionManager _regionManager;
        private readonly IEventAggregator _eventAggregator;

        private object _currentView;
        private IRegion _mainRegion;

        public MainRegionController(IUnityContainer container, 
                                    IRegionManager regionManager, 
                                    IEventAggregator eventAggregator)
        {
            _container = container;
            _regionManager = regionManager;
            _eventAggregator = eventAggregator;

            Initialize();
        }

        private void Initialize()
        {
            _eventAggregator.GetEvent<PageSelectedEvent>().Subscribe(PageSelected, ThreadOption.UIThread, true);
            _mainRegion = _regionManager.Regions["MainRegion"];
        }

        private void PageSelected(IPage page)
        {
            if (page != null)
            {
                ShowPage(page);
            }
        }

        private void ShowPage(IPage page)
        {
            object newView = page.View;

            if (_currentView != null)
            {
                _mainRegion.Remove(_currentView);
            }

            if (newView != null)
            {
                _mainRegion.Add(newView);
                _mainRegion.Activate(newView);
            }

            _currentView = newView;
        }
    }
}