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Pro Aspnet MVC 4读书笔记(3)

Listing 4-1. The Initial Content of the Home Controller

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

    }
}

View Code

Listing 4-2. The Contents of the Result View File

@model String

@{
    Layout = null;
}

<!DOCTYPE html>

<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Result</title>
</head>
<body>
    <div>
        @Model    
    </div>
</body>
</html>

View Code

Listing 4-3. Defining a Property

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace LanguageFeatures.Models
{
    public class Product
    {
        private string name;

        public string Name
        {
            get { return name; }
            set { name = value; }
        }
    }
}

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Listing 4-4. Consuming a Property

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        public ViewResult AutoProperty()
        {
            Product product = new Product();
            product.Name = "Kayak";

            string productName = product.Name;

            return View("Result", (object)String.Format("Product name: {0}", productName));
        }
    }
}

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Listing 4-5. Verbose Property Definitions

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace LanguageFeatures.Models
{
    public class Product
    {
        private int productId;
        private string name;
        private string description;
        private decimal price;
        private string category;

        public int ProductId
        {
            get { return productId; }
            set { productId = value; }
        }

        public string Name
        {
            get { return name; }
            set { name = value; }
        }

        public string Description
        {
            get { return description; }
            set { description = value; }
        }

        public decimal Price
        {
            get { return price; }
            set { price = value; }
        }

        public string Category
        {
            get { return category; }
            set { category = value; }
        }
    }
}

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Listing 4-6. Using Automatically Implemented Properties

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace LanguageFeatures.Models
{
    public class Product
    {
        public int ProductId { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }
        public decimal Price { get; set; }
        public string Category { get; set; }
    }
}

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Listing 4-7. Reverting from an Automatic to a Regular Property

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace LanguageFeatures.Models
{
    public class Product
    {
        private string name;

        public int ProductId { get; set; }

        public string Name
        {
            get {
                return ProductId + name;
            }
            set {
                name = value;
            }
        }
        public string Description { get; set; }
        public decimal Price { get; set; }
        public string Category { get; set; }
    }
}

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Listing 4-8. Constructing and Initializing an Object with Properties

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        public ViewResult AutoProperty()
        {
            Product product = new Product();
            product.Name = "Kayak";

            string productName = product.Name;

            return View("Result", (object)String.Format("Product name: {0}", productName));
        }

        public ViewResult CreateProduct()
        {
            Product product = new Product();
            product.ProductId = 100;
            product.Name = "Kayak";
            product.Description = "A boat for one person";
            product.Price = 275M;
            product.Category = "Watersports";

            return View("Result", (object)String.Format("Category: {0}", product.Category));
        }
    }
}

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Listing 4-9. Using the Object Initializer Feature

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        public ViewResult AutoProperty()
        {
            Product product = new Product();
            product.Name = "Kayak";

            string productName = product.Name;

            return View("Result", (object)String.Format("Product name: {0}", productName));
        }

        public ViewResult CreateProduct()
        {
            Product product = new Product { 
                ProductId = 100,
                Name = "Kayak",
                Description = "A boat for one person",
                Price = 275M,
                Category = "Waterports"
            };

            return View("Result", (object)String.Format("Category: {0}", product.Category));
        }
    }
}

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Listing 4-10. Initializing Collections and Arrays

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        public ViewResult AutoProperty()
        {
            Product product = new Product();
            product.Name = "Kayak";

            string productName = product.Name;

            return View("Result", (object)String.Format("Product name: {0}", productName));
        }

        public ViewResult CreateProduct()
        {
            Product product = new Product { 
                ProductId = 100,
                Name = "Kayak",
                Description = "A boat for one person",
                Price = 275M,
                Category = "Waterports"
            };

            return View("Result", (object)String.Format("Category: {0}", product.Category));
        }

        public ViewResult CreateCollection()
        {
            string[] stringArray = { "apple", "orange", "plum"};
            List<int> intList = new List<int> { 10, 20, 30, 40 };
            Dictionary<string, int> dict = new Dictionary<string, int> { 
                { "apple", 10 },
                { "orange", 20 },
                { "plum", 30 }
            };

            return View("Result", (object)stringArray[1]);
        }
    }
}

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Listing 4-11. The ShoppingCart Class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace LanguageFeatures.Models
{
    public class ShoppingCart
    {
        public List<Product> Products { get; set; }
    }
}

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Listing 4-12. Defining an Extension Method

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace LanguageFeatures.Models
{
    public static class MyExtensionMethods
    {
        public static decimal TotalPrices(this ShoppingCart cart)
        {
            decimal total = 0;

            foreach (Product prod in cart.Products)
            {
                total += prod.Price;
            }

            return total;
        }
    }
}

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Listing 4-13. Applying an Extension Method

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult UseExtension()
        {
            // Create and populate ShoppingCart
            ShoppingCart cart = new ShoppingCart
            {
                Products = new List<Product> { 
                    new Product{Name = "Kayak", Price = 275M},
                    new Product{Name = "Lifejacket", Price = 48.95M},
                    new Product{Name = "Soccer ball", Price = 19.50M},
                    new Product{Name = "Corner flag", Price = 34.95M}
                }
            };

            // Get the total value of the products in the cart
            decimal cartTotal = cart.TotalPrices();

            return View("Result", (object)String.Format("Total: {0:c}", cartTotal));
        }
    }
}

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Listing 4-14. Implementing an Interface in the ShoppingCart Class

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace LanguageFeatures.Models
{
    public class ShoppingCart : IEnumerable<Product>
    {
        public List<Product> Products { get; set; }

        public IEnumerator<Product> GetEnumerator()
        {
            return Products.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }
    }
}

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Listing 4-15. An Extension Method That Works on an Interface

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace LanguageFeatures.Models
{
    public static class MyExtensionMethods
    {
        public static decimal TotalPrices(this IEnumerable<Product> productEnum)
        {
            decimal total = 0;

            foreach (Product prod in productEnum)
            {
                total += prod.Price;
            }

            return total;
        }
    }
}

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Listing 4-16. Applying an Extension Method to Different Implementations of the Same Interface

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult UseExtensionEnumerable()
        {
            IEnumerable<Product> products = new ShoppingCart
            {
                Products = new List<Product> { 
                    new Product{Name = "Kayak", Price = 275M},
                    new Product{Name = "Lifejacket", Price = 48.95M},
                    new Product{Name = "Soccer ball", Price = 19.50M},
                    new Product{Name = "Corner flag", Price = 34.95M}
                }
            };

            Product[] productArray = {
                new Product{Name = "Kayak", Price = 275M},
                new Product{Name = "Lifejacket", Price = 48.95M},
                new Product{Name = "Soccer ball", Price = 19.50M},
                new Product{Name = "Corner flag", Price = 34.95M}
            };

            decimal cartTotal = products.TotalPrices();
            decimal arrayTotal = productArray.TotalPrices();

            return View("Result", 
                (object)String.Format("Cart Total: {0}, Array Total: {1}", 
                cartTotal, arrayTotal));
        }
    }
}

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Listing 4-17. A Filtering Extension Method

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace LanguageFeatures.Models
{
    public static class MyExtensionMethods
    {
        public static decimal TotalPrices(this IEnumerable<Product> productEnum)
        {
            decimal total = 0;

            foreach (Product prod in productEnum)
            {
                total += prod.Price;
            }

            return total;
        }

        public static IEnumerable<Product> FilterByCategory(
            this IEnumerable<Product> productEnum, string category)
        {
            foreach (Product prod in productEnum)
            {
                if (prod.Category == category)
                {
                    yield return prod;
                }
            }
        }
    }
}

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Listing 4-18. Using the Filtering Extension Method

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult UseFilterExtensionMethod()
        {
            IEnumerable<Product> products = new ShoppingCart
            {
                Products = new List<Product> { 
                    new Product{Name = "Kayak", Category = "Watersports", Price = 275M},
                    new Product{Name = "Lifejacket", Category = "Watersports", Price = 48.95M},
                    new Product{Name = "Soccer ball", Category = "Soccer", Price = 19.50M},
                    new Product{Name = "Corner flag", Category = "Soccer", Price = 34.95M}
                }
            };

            decimal total = 0;

            foreach (Product prod in products.FilterByCategory("Soccer"))
            {
                total += prod.Price;
            }

            return View("Result", (object)String.Format("Total: {0}", total));
        }
    }
}

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Listing 4-19. Using a Delegate in an Extension Method

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace LanguageFeatures.Models
{
    public static class MyExtensionMethods
    {
        public static decimal TotalPrices(this IEnumerable<Product> productEnum)
        {
            decimal total = 0;

            foreach (Product prod in productEnum)
            {
                total += prod.Price;
            }

            return total;
        }

        public static IEnumerable<Product> FilterByCategory(
            this IEnumerable<Product> productEnum, string category)
        {
            foreach (Product prod in productEnum)
            {
                if (prod.Category == category)
                {
                    yield return prod;
                }
            }
        }

        public static IEnumerable<Product> Filter(
            this IEnumerable<Product> productEnum, Func<Product, bool> selector)
        {
            foreach (Product prod in productEnum)
            {
                if (selector(prod))
                {
                    yield return prod;
                }
            }
        }
    }
}

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Listing 4-20. Using the Filtering Extension Method with a Func

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult UseFilterExtensionMethod()
        {
            IEnumerable<Product> products = new ShoppingCart
            {
                Products = new List<Product> { 
                    new Product{Name = "Kayak", Category = "Watersports", Price = 275M},
                    new Product{Name = "Lifejacket", Category = "Watersports", Price = 48.95M},
                    new Product{Name = "Soccer ball", Category = "Soccer", Price = 19.50M},
                    new Product{Name = "Corner flag", Category = "Soccer", Price = 34.95M}
                }
            };

            Func<Product, bool> categoryFilter = delegate(Product prod)
            {
                return prod.Category == "Soccer";
            };

            decimal total = 0;

            foreach (Product prod in products.Filter(categoryFilter))
            {
                total += prod.Price;
            }

            return View("Result", (object)String.Format("Total: {0}", total));
        }
    }
}

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Listing 4-21. Using a Lambda Expression to Replace a Delegate Definition

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult UseFilterExtensionMethod()
        {
            IEnumerable<Product> products = new ShoppingCart
            {
                Products = new List<Product> { 
                    new Product{Name = "Kayak", Category = "Watersports", Price = 275M},
                    new Product{Name = "Lifejacket", Category = "Watersports", Price = 48.95M},
                    new Product{Name = "Soccer ball", Category = "Soccer", Price = 19.50M},
                    new Product{Name = "Corner flag", Category = "Soccer", Price = 34.95M}
                }
            };

            Func<Product, bool> categoryFilter =  prod => prod.Category == "Soccer";

            decimal total = 0;

            foreach (Product prod in products.Filter(categoryFilter))
            {
                total += prod.Price;
            }

            return View("Result", (object)String.Format("Total: {0}", total));
        }
    }
}

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Listing 4-22. A Lambda Expression Without a Func

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult UseFilterExtensionMethod()
        {
            IEnumerable<Product> products = new ShoppingCart
            {
                Products = new List<Product> { 
                    new Product{Name = "Kayak", Category = "Watersports", Price = 275M},
                    new Product{Name = "Lifejacket", Category = "Watersports", Price = 48.95M},
                    new Product{Name = "Soccer ball", Category = "Soccer", Price = 19.50M},
                    new Product{Name = "Corner flag", Category = "Soccer", Price = 34.95M}
                }
            };

            decimal total = 0;

            foreach (Product prod in products.Filter(prod => prod.Category == "Soccer"))
            {
                total += prod.Price;
            }

            return View("Result", (object)String.Format("Total: {0}", total));
        }
    }
}

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Listing 4-23. Extending the Filtering Expressed by the Lambda Expression

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult UseFilterExtensionMethod()
        {
            IEnumerable<Product> products = new ShoppingCart
            {
                Products = new List<Product> { 
                    new Product{Name = "Kayak", Category = "Watersports", Price = 275M},
                    new Product{Name = "Lifejacket", Category = "Watersports", Price = 48.95M},
                    new Product{Name = "Soccer ball", Category = "Soccer", Price = 19.50M},
                    new Product{Name = "Corner flag", Category = "Soccer", Price = 34.95M}
                }
            };

            decimal total = 0;

            foreach (Product prod in products.Filter(
                prod => prod.Category == "Soccer" || prod.Price > 20))
            {
                total += prod.Price;
            }

            return View("Result", (object)String.Format("Total: {0}", total));
        }
    }
}

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Listing 4-24. Using Type Inference

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult UseTypeInference()
        {
            var myVariable = new Product { Name = "Kayak", Category = "Watersports", Price = 275M };

            string name = myVariable.Name; // Legal
            int price = myVariable.Price;  // Compiler error

            return View("Result", (object)String.Format("Name: {0}, Price: {1}", name, price));
        }
    }
}

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Listing 4-25. Creating an Anonymous Type

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult UseTypeInference()
        {
            var myAnonType = new { Name = "Kayak", Category = "Watersports", Price = 275M };

            string name = myAnonType.Name; 
            decimal price = myAnonType.Price;  

            return View("Result", (object)String.Format("Name: {0}, Price: {1}", name, price));
        }
    }
}

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Listing 4-26. Creating an Array of Anonymously Typed Objects

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult CreateAnonArray()
        {
            var oddsAnonEnds = new[] { 
                new {Name = "MVC", Category = "Pattern"}, 
                new {Name = "Hat", Category = "Clothing"}, 
                new {Name = "Apple", Category = "Fruit"}
            };

            StringBuilder result = new StringBuilder();
            foreach (var item in oddsAnonEnds)
            {
                result.Append(item.Name).Append(" ");
            }

            return View("Result", (object)result.ToString());
        }
    }
}

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Listing 4-27. Querying Without LINQ

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult FindProducts()
        {
            Product[] products = 
            {
                new Product {Name = "Kayak", Category = "Watersports", Price = 275M},
                new Product {Name = "Lifejacket", Category = "Watersports", Price = 48.95M},
                new Product {Name = "Soccer ball", Category = "Soccer", Price = 19.50M},
                new Product {Name = "Corner flag", Category = "Soccer", Price = 34.95M}
            };

            Product[] foundProducts = new Product[3];

            Array.Sort(products, (item1, item2) => {
                return Comparer<decimal>.Default.Compare(item1.Price, item2.Price);
            });

            Array.Copy(products, foundProducts, 3);

            StringBuilder result = new StringBuilder();
            foreach (Product p in foundProducts)
            {
                result.AppendFormat("Price: {0} ", p.Price);
            }

            return View("Result", (object)result.ToString());
        }
    }
}

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Listing 4-28. Using LINQ to Query Data

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult FindProducts()
        {
            Product[] products = 
            {
                new Product {Name = "Kayak", Category = "Watersports", Price = 275M},
                new Product {Name = "Lifejacket", Category = "Watersports", Price = 48.95M},
                new Product {Name = "Soccer ball", Category = "Soccer", Price = 19.50M},
                new Product {Name = "Corner flag", Category = "Soccer", Price = 34.95M}
            };

            var foundProducts = from match in products
                                orderby match.Price descending
                                select new { 
                                    match.Name,
                                    match.Price
                                };

            int count = 0;

            StringBuilder result = new StringBuilder();
            foreach (var p in foundProducts)
            {
                result.AppendFormat("Price: {0} ", p.Price);
                if (++count == 3)
                {
                    break;
                }
            }

            return View("Result", (object)result.ToString());
        }
    }
}

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Listing 4-29. Using LINQ Dot Notation

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult FindProducts()
        {
            Product[] products = 
            {
                new Product {Name = "Kayak", Category = "Watersports", Price = 275M},
                new Product {Name = "Lifejacket", Category = "Watersports", Price = 48.95M},
                new Product {Name = "Soccer ball", Category = "Soccer", Price = 19.50M},
                new Product {Name = "Corner flag", Category = "Soccer", Price = 34.95M}
            };

            var foundProducts = products.OrderByDescending(e => e.Price)
                .Take(3)
                .Select(e => new {
                    e.Name,
                    e.Price
                });

            int count = 0;

            StringBuilder result = new StringBuilder();
            foreach (var p in foundProducts)
            {
                result.AppendFormat("Price: {0} ", p.Price);
                if (++count == 3)
                {
                    break;
                }
            }

            return View("Result", (object)result.ToString());
        }
    }
}

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Listing 4-30. Using Deferred LINQ Extension Methods in a Query

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult FindProducts()
        {
            Product[] products = 
            {
                new Product {Name = "Kayak", Category = "Watersports", Price = 275M},
                new Product {Name = "Lifejacket", Category = "Watersports", Price = 48.95M},
                new Product {Name = "Soccer ball", Category = "Soccer", Price = 19.50M},
                new Product {Name = "Corner flag", Category = "Soccer", Price = 34.95M}
            };

            var foundProducts = products.OrderByDescending(e => e.Price)
                .Take(3)
                .Select(e => new {
                    e.Name,
                    e.Price
                });

            products[2] = new Product { Name = "Stadium", Price = 79600M };

            StringBuilder result = new StringBuilder();
            foreach (var p in foundProducts)
            {
                result.AppendFormat("Price: {0} ", p.Price);
            }

            return View("Result", (object)result.ToString());
        }
    }
}

View Code

Listing 4-31. An Immediately Executed LINQ Query

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.Mvc;
using LanguageFeatures.Models;

namespace LanguageFeatures.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Navigate to a URL to show an example";
        }

        // Other action methods omitted for brevity

        public ViewResult SumProducts()
        {
            Product[] products = 
            {
                new Product {Name = "Kayak", Category = "Watersports", Price = 275M},
                new Product {Name = "Lifejacket", Category = "Watersports", Price = 48.95M},
                new Product {Name = "Soccer ball", Category = "Soccer", Price = 19.50M},
                new Product {Name = "Corner flag", Category = "Soccer", Price = 34.95M}
            };

            var results = products.Sum(e => e.Price);

            products[2] = new Product { Name = "Stadium", Price = 79600M };

            return View("Result", (object)String.Format("Sum: {0:c}", results));
        }
    }
}

View Code

Listing 4-32. A Simple Asynchronous Method

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Net.Http;
using System.Threading.Tasks;

namespace LanguageFeatures.Models
{
    public class MyAsyncMethods
    {
        public static Task<long?> GetPageLength()
        {
            HttpClient client = new HttpClient();
            var httpTask = client.GetAsync("http://apress.com");

            // We could do other things here while we are waiting
            // for the HTTP request to complete

            return httpTask.ContinueWith((Task<HttpResponseMessage> antecedent) => {
                return antecedent.Result.Content.Headers.ContentLength;
            });
        }
    }
}

View Code

Listing 4-33. Using the async and await Keywords

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Net.Http;
using System.Threading.Tasks;

namespace LanguageFeatures.Models
{
    public class MyAsyncMethods
    {
        public async static Task<long?> GetPageLength()
        {
            HttpClient client = new HttpClient();
            var httpMessage = await client.GetAsync("http://apress.com");

            // We could do other things here while we are waiting
            // for the HTTP request to complete

            return httpMessage.Content.Headers.ContentLength;
        }
    }
}

View Code

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原文地址：https://www.cnblogs.com/thlzhf/p/3528077.html