protected override ComposablePartCatalog PrepareCompositionCatalog()
        {
            // Create alternative AggregateCatalog to group recomposition events.
            var currentCatalogs = Composition.AggregateCatalog.Catalogs.ToList();
            var catalog = new AggregateCatalog();
 
            // Add current catalogs as a single group
            catalog.Catalogs.Add(new AggregateCatalog(currentCatalogs));
            Composition.Recomposed +=
                (sender, args) =>
                {
                    // Find new catalogs.
                    var newCats =
                        Composition.AggregateCatalog.Catalogs.Where(c => !currentCatalogs.Contains(c)).ToList();
                    currentCatalogs.AddRange(newCats);
 
                    // Add new catalogs as a single group
                    catalog.Catalogs.Add(new AggregateCatalog(newCats));
                };
 
            return catalog;
        }