Adding a view component for cart summary

1. Added a View component named CartSummary
2. Moved the CartSummary.cshtml as default.cshtml to shared\Components

src/MusicStore/Components/CartSummaryComponent.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNet.Mvc;
+using MusicStore.Models;
+
+namespace MusicStore.Components
+{
+    [ViewComponent(Name = "CartSummary")]
+    public class CartSummaryComponent : ViewComponent
+    {
+        private MusicStoreContext db = new MusicStoreContext();
+        public async Task<IViewComponentResult> InvokeAsync()
+        {
+            var cart = ShoppingCart.GetCart(db, this.Context);
+
+            var cartItems = cart.GetCartItems()
+                .Select(a => a.Album.Title)
+                .OrderBy(x => x);
+
+            //Bug: Uncommenting results in compilation error. 
+            //ViewBag.CartCount = cartItems.Count();
+            //ViewBag.CartSummary = string.Join("\n", cartItems.Distinct());
+
+            return View();
+        }
+    }
+}

src/MusicStore/Views/Shared/_Layout.cshtml

@@ -27,8 +27,7 @@
                 <ul class="nav navbar-nav">
                     <li>@Html.ActionLink("Home", "Index", "Home")</li>
                     @await Component.InvokeAsync("GenreMenu")
-                    @*Bug: HtmlHelper missing*@
+                    @*@await Component.InvokeAsync("CartSummary")*@
-                    @*@Html.Action("CartSummary", "ShoppingCart")*@
                 </ul>
                 @await Html.PartialAsync("_LoginPartial")
             </div>