Fixing compilation errors in the view components.

Marked one of the controller actions with [HttpGet] to prevent it being chosen for non get methods.

src/MusicStore/Components/CartSummaryComponent.cs

@@ -1,8 +1,7 @@
-using System;
+using Microsoft.AspNet.Mvc;
+using MusicStore.Models;
 using System.Linq;
 using System.Threading.Tasks;
-using Microsoft.AspNet.Mvc;
-using MusicStore.Models;
 
 namespace MusicStore.Components
 {
@@ -18,16 +17,23 @@ namespace MusicStore.Components
 
         public async Task<IViewComponentResult> InvokeAsync()
         {
-            var cart = ShoppingCart.GetCart(db, this.Context);
-
-            var cartItems = cart.GetCartItems()
-                .Select(a => a.Album.Title)
-                .OrderBy(x => x);
+            var cartItems = await GetCartItems();
 
             ViewBag.CartCount = cartItems.Count();
             ViewBag.CartSummary = string.Join("\n", cartItems.Distinct());
 
             return View();
         }
+
+        private Task<IOrderedEnumerable<string>> GetCartItems()
+        {
+            var cart = ShoppingCart.GetCart(db, this.Context);
+
+            var cartItems = cart.GetCartItems()
+                .Select(a => a.Album.Title)
+                .OrderBy(x => x);
+
+            return Task.FromResult(cartItems);
+        }
     }
 }

src/MusicStore/Components/GenreMenuComponent.cs

@@ -3,6 +3,7 @@ using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Mvc;
 using MusicStore.Models;
+using System.Collections.Generic;
 
 namespace MusicStore.Components
 {
@@ -17,6 +18,13 @@ namespace MusicStore.Components
         }
 
         public async Task<IViewComponentResult> InvokeAsync()
+        {
+            var genres = await GetGenres();
+
+            return View(genres);
+        }
+
+        private Task<List<Genre>> GetGenres()
         {
             // TODO [EF] We don't query related data as yet, so the OrderByDescending isn't doing anything
             //var genres = db.Genres
@@ -28,8 +36,7 @@ namespace MusicStore.Components
             //.ToList();
 
             var genres = db.Genres.ToList();
-
-            return View(genres);
+            return Task.FromResult(genres);
         }
     }
 }

src/MusicStore/Controllers/CheckoutController.cs

@@ -22,6 +22,7 @@ namespace MusicStore.Controllers
         //
         // GET: /Checkout/
 
+        [HttpGet]
         public IActionResult AddressAndPayment()
         {
             return View();