Presentation Model (MVVM) Good Practices

using System;
using System.Collections.Generic;
using System.Text;
using PresentationModelBase;

namespace App.Core
{
    public class MainViewPresentationModel : ClosableViewPresentationModel, IMainViewPresentationModel
    {
        public MainViewPresentationModel()
        {
            _navigationItems = Get<ICollection<ICustomActionPresentationModel>>();
            _workspaces = Get<ICollection<ISelectableViewPresentationModel>>();

            CreateNavigationItems();
        }

        private void CreateNavigationItems()
        {
            ICustomActionPresentationModel openNewProductView = Get<ICustomActionPresentationModel>();
            openNewProductView.Owner = this;
            openNewProductView.ActionName = "CreateNew";
            openNewProductView.TypeParameters = new Type[] { typeof(Product) };
            openNewProductView.DisplayName = "Create new product";

            ICustomActionPresentationModel openProductsView = Get<ICustomActionPresentationModel>();
            openProductsView.Owner = this;
            openProductsView.ActionName = "ViewAll";
            openProductsView.TypeParameters = new Type[] { typeof(Product) };
            openProductsView.DisplayName = "View all products";

            _navigationItems.Add(openNewProductView);
            _navigationItems.Add(openProductsView);
        }

        private ICollection<ICustomActionPresentationModel> _navigationItems;
        public ICollection<ICustomActionPresentationModel> NavigationItems
        {
            get { return _navigationItems; }
        }

        private ICollection<ISelectableViewPresentationModel> _workspaces;
        public ICollection<ISelectableViewPresentationModel> Workspaces
        {
            get { return _workspaces; }
        }

        public void CreateNew<T>()
            where T : new()
        {
            IEntityViewPresentationModel<T> workspace = Get<IEntityViewPresentationModel<T>>();
            workspace.Entity = new T();
            AddWorkspace(workspace);
        }

        public void EditExisting<T>(T item)
            where T : new()
        {
            IEntityViewPresentationModel<T> workspace = Get<IEntityViewPresentationModel<T>>();
            workspace.Entity = item;
            AddWorkspace(workspace);
        }

        public void ViewAll<T>()
            where T : new()
        {
            IEntityCollectionViewPresentationModel<T> workspace = Get<IEntityCollectionViewPresentationModel<T>>();
            AddWorkspace(workspace);
        }

        void AddWorkspace(ISelectableViewPresentationModel workspace)
        {
            if (!_workspaces.Contains(workspace))
            {
                workspace.RequestClose +=
                       (sender, e) => OnWorkspaceRequestClose(sender);
                Workspaces.Add(workspace);
            }
            SetActiveWorkspace(workspace);
        }

        void OnWorkspaceRequestClose(object sender)
        {
            ISelectableViewPresentationModel workspace = sender as SelectableViewPresentationModel;
            Workspaces.Remove(workspace);
        }

        protected virtual void SetActiveWorkspace(ISelectableViewPresentationModel workspace)
        {
            workspace.IsSelected = true;
        }
    }
}