Navigating the different modules through a TreeView and ToolBar with Prism

using System.Collections.ObjectModel;
using System.ComponentModel.Composition;
using System.Linq;
using Microsoft.Practices.Prism.Regions;
using NavInfrastructure;
using NavModule_One.Models;

namespace NavModule_One.ViewModels
{
    [Export]
    [PartCreationPolicy(CreationPolicy.NonShared)]
    public class CatalogViewModel : ViewModelBase, INavigationAware
    {
        #region Private Field
        // Assing Cache - devlop EnterpriceLibrary
        [Import]
        protected CacheManager _cacheManager;
        #endregion
        #region .ctor
        public CatalogViewModel()
        {
            // fire ctor in Base class.
            // and assing GlobalCommand as CompositeCommand.
        }
        #endregion
        #region Property CurrentItem
        /// <summary>
        /// Current base item.
        /// </summary>
        public EntityBase CurrentItem
        {
            get { return _currentItem; }
            private set
            {
                if (value != _currentItem)
                {
                    _currentItem = value;
                    this.RaisePropertyChanged("CurrentItem");
                }
            }
        }
        private EntityBase _currentItem;
        #endregion
        #region Property CatalogItems
        private ObservableCollection<EntityBase> _catalogItems;
        public ObservableCollection<EntityBase> CatalogItems // 
        {
            get { return _catalogItems ?? (_catalogItems = new ObservableCollection<EntityBase>()); }
            set
            {
                _catalogItems = value;
                RaisePropertyChanged("CatalogItems");
            }
        }
        #endregion
        #region INavigationAware Members
        public bool IsNavigationTarget(NavigationContext navigationContext)
        {
            // Only one view.
            return true;
        }
        public void OnNavigatedFrom(NavigationContext navigationContext)
        {
        }
        public void OnNavigatedTo(NavigationContext navigationContext)
        {
            var idEntity = int.Parse(navigationContext.Parameters["ParentId"]);
            this.CurrentItem = _cacheManager.CacheDocuments.Single(i => i.IDEntity == idEntity);
            PopulateViewModel();
        }
        #endregion
        #region Help method
        private void PopulateViewModel()
        {
            CatalogItems.Clear();
            foreach (var i in _cacheManager.CacheDocuments.Where(i => i.Parent != null && i.Parent.IDEntity == _currentItem.IDEntity))
            {
                CatalogItems.Add(i);
            }
        }
        #endregion
    }
}