BooksUniversalApp.App.RegisterServices C# (CSharp) Method

        private IServiceProvider RegisterServices()
        {
            var serviceCollection = new ServiceCollection();
            serviceCollection.AddTransient<BooksViewModel>();
            serviceCollection.AddTransient<BookViewModel>();
            serviceCollection.AddSingleton<IBooksService, BooksService>();
            serviceCollection.AddSingleton<IBooksRepository, BooksSampleRepository>();
            return serviceCollection.BuildServiceProvider();
        }