simple ViewModel locator

ViewModelIndexer.cs

using System;
using System.ComponentModel.Composition;
using System.Collections.Generic;
using System.Linq;

namespace Samples
{
    public class ViewModelIndexer
    {
        public ViewModelIndexer()
        {
            CompositionInitializer.SatisfyImports(this);
            IsShared = false;
        }

        [ImportMany(typeof(ViewModelBase), AllowRecomposition = true)]
        public IEnumerable<Lazy<ViewModelBase, IViewModelMetadata>> ViewModelsLazy { get; set; }

        [ImportMany(typeof(ViewModelBase), AllowRecomposition = true)]
        public IEnumerable<ExportFactory<ViewModelBase, IViewModelMetadata>> ViewModelsFactories { get; set; }

        private ViewModelBase GetViewModel(string viewModel)
        {
            if (IsShared)
            {
                return ViewModelsLazy.Single(v => v.Metadata.Name.Equals(viewModel)).Value;
            }

            var context = ViewModelsFactories.Single(v => v.Metadata.Name.Equals(viewModel)).CreateExport();
            return context.Value;
        }

        /// <summary>
        /// True/False whether to return singleton view models
        /// or a new instance per request.
        /// </summary>
        public bool IsShared { get; set; }

        public ViewModelBase this[string viewModel]
        {
            get { return GetViewModel(viewModel); }
        }
    }
}