INavigationItem.cs

    public interface INavigationItem<out T> where T : class, IViewModel
    {
        Type ViewModelType { get; set; }

        object ViewModel { get; set; }
    }

INavigationService.cs

    public interface INavigationService
    {
        void ShowMasterPage();
        void HideMasterPage();
        
        //...
    }

MenuViewModel.cs

    public class MenuViewModel : ViewModelBase
    {
        Command navigateCommand;
        public Command NavigateCommand => navigateCommand ?? (navigateCommand = new Command(async (index) => await NavigateAsync((int)index)));

        public ObservableRangeCollection<INavigationItem<ViewModelBase>> NavigationItems { get; } = new ObservableRangeCollection<INavigationItem<ViewModelBase>>();

        public MenuViewModel()
        {
            NavigationItems.AddRange(new INavigationItem<ViewModelBase>[]
            {
                new NavigationItem<FeedViewModel>(),
                new NavigationItem<FriendsViewModel>(),
                new NavigationItem<GroupsViewModel>(),
                new NavigationItem<SettingsViewModel>(),
            });
        }

        private async Task NavigateAsync(int index)
        {
            NavigationService.Instance.HideMasterPage();

            //TODO: maybe faster without reflection
            var navigationItem = NavigationItems[index];
            dynamic viewModel = navigationItem.ViewModel ?? (navigationItem.ViewModel = Activator.CreateInstance(navigationItem.ViewModelType));

            await Task.Delay(225);

            NavigationService.Instance.SwitchDetailPage(viewModel);
        }

NavigationItem.cs

    public class NavigationItem<T> : INavigationItem<T> where T : class, IViewModel
    {
        public Type ViewModelType { get; set; }

        public object ViewModel { get; set; }

        public NavigationItem()
        {
            ViewModelType = typeof(T);
        }
    }

NavigationService.cs

    public class NavigationService : INavigationService
    {
        MasterDetailPage MasterPage
        {
            get { return Application.Current.MainPage as MasterDetailPage; }
        }

        public void ShowMasterPage()
        {
            if(MasterPage != null)
                MasterPage.IsPresented = true;
        }

        public void HideMasterPage()
        {
            if (MasterPage != null)
                MasterPage.IsPresented = false;
        }
        
        //...
    }