C#开发的进化史

1、数据类型的进化

 C#1中实现Product类型代码

public class Product
    {
        string name;
        public string Name
        {
            get { return name; }
        }

        decimal price;
        public decimal Price
        {
            get { return price; }
        }

        public Product(string name, decimal price)
        {
            this.name = name;
            this.price = price;
        }
     
        public static ArrayList GetSampleProducts()
        {
            ArrayList list = new ArrayList();
            list.Add(new Product("West Side Story", 9.99m));
            list.Add(new Product("Assassins", 14.99m));
            list.Add(new Product("Frogs", 13.99m));
            list.Add(new Product("Sweeney Todd", 10.99m));
            return list;
           
        }

        public override string ToString()
        {
            return string.Format("{0}: {1}", name, price);
          
        }
      

    }

C#2中的强类型集合和私有的赋值方法

 public class Product
    {
        string name;
        public string Name
        {
            get { return name; }
            private set { Name = value; } 私有的赋值方法
        }

        decimal price;
        public decimal Price
        {
            get { return price; }
            private set { Price = value; }
        }
        //C#3:Product(){}
        public Product(string name, decimal price)
        {
           
              Name = name;
              Price = price;
        }
      public static List<Product>GetSampleProducts()
        {
             List<Product>list= new List<Product>();
            list.Add(new Product("West Side Story", 9.99m));
            list.Add(new Product("Assassins", 14.99m));
            list.Add(new Product("Frogs", 13.99m));
            list.Add(new Product("Sweeney Todd", 10.99m));
            return list;
           
        }

        public override string ToString()
        {
            return string.Format("{0}: {1}", name, price);
          
        }

    }

C#3自动实现的属性和更简单的初始化

 public class Product
    {
        public string Name { get; private set; }
        public string Price { get; private set; }

        public Product(string name, decimal price)
        {
           
              Name = name;
              Price = price;
        }

        private Product()
        {
        }

        public static List<Product> GetSampleProducts()
        {
            return new List<Product>
            {
                new Product {Name = "West Side Story", Price = 9.99m},
                new Product {Name = "Assassins", Price = 14.99m},
                new Product {Name = "Frogs", Price = 13.99m},
                new Product {Name = "Sweeney Todd", Price = 10.99m}
            };
        }

        public override string ToString()
        {
            return string.Format("{0}: {1}", Name, Price);
        }
      
    }

C#4中命名实参

public class Product
    {
     
        public override string ToString()
        {
            return string.Format("{0}: {1}", name, price);
        }
        //C#4中的参数：尽管私有赋值不能被公共的改变，但如果要求它也不能被私有的改变，将会更加的清晰，在C#4中，我们用调用构造函数时指定实参的名称
        readonly string name;
        public string Name { get { return name; } }
        return new List<Product>
        {
            new Product {name = "West Side Story", price = 9.99m},
            new Product {name = "Assassins", price = 14.99m},
            new Product {name = "Frogs", price = 13.99m},
            new Product {name = "Sweeney Todd", price = 10.99m},
        };


    }

2、排序和过滤的演化

 1、排序

C#1中使用IComparer对ArrayList进行排序

class ProductNameComparer : IComparer
        {
            public int Compare(object x, object y)
            {
                Product first = (Product)x;
                Product second = (Product)y;
                return first.Name.CompareTo(second.Name);
            }
        }
 static void Main()
        {
            ArrayList products = Product.GetSampleProducts();
            products.Sort(new ProductNameComparer());
            foreach (Product product in products)
            {
                Console.WriteLine(product);
            }
        }

C#2中使用IComparer<product>对List<Product>进行排序

 class ProductNameComparer : IComparer<Product>
        {
            public int Compare(Product x, Product y)
            {
                return x.Name.CompareTo(y.Name);
            }
        }
static void Main()
{
 List<Product> products = Product.GetSampleProducts();
 products.Sort(new ProductNameComparer());
            foreach (Product product in products)
            {
                Console.WriteLine(product);
            }
}

C#2中使用委托进行比较

 /* 
         * C#2的方法1确实有了一定的改进，但是我们希望能直接指定要进行的标胶，就能开始对产品进行排序，而不需要实现一个接口来做这件事
         * 下面它告诉sort方法如何用一个委托来比较俩个产品.省略了接口实现的代码和products.Sort(new ProductNameComparer());
         * List<Product> products = Product.GetSampleProducts();
         * products.Sort（delegate （Product x，Product y）
         * {return x.Name.CompareTo(y.Name);}
         * ）;
         */

C#3中使用lambda表达式进行比较

 List<Product> products = Product.GetSampleProducts();
products.Sort(（x,y）=>x.Name.CompareTo(y.Name));
foreach（Product product in products）
{
         console.writeline(product);
}
C#3还有另一种写法排序
foreach（Product product in product.OrderBy（p=>p.Name））
{
         console.writeline(product);//通知轻松的按顺序打印名称，同时不必修改原产品列表
}

  2、查询

   循环、测试和打印（C#1）

 ArrayList products = Product.GetSampleProducts();
            foreach (Product product in products.Cast<Product>().Where(product => product.Price > 10m))
            {
                Console.WriteLine(product);
            }

  测试和打印分开进行（C#2）

List<Product> products =Product.GetSampleProducts();
          Predicate<Product> test = delegate(Product p){ return p.Price > 10m;};
           List<Product>  matches=products.FindAll(test);
          Action<Product> print=console.writeLine;
          matches.ForEach(print);

测试和打印分开进行的另一个版本（C#2）

List<Product> products =Product.GetSampleProducts();
products.FindAll（delegate （Product p）{ return p.Price >10;}）.ForEach(Console.WriteLine);

用lambda表达式来进行测试（c#3）

List<Product> products =Product.GetSampleProducts();
foreach（Product product in products.Where（p=>p.price>10））
{
    Console.WriteLine(product);
}
              

C#中使用Linq表达式

foreach (Product product in products.Cast<Product>().Where(product => product.Price > 10m))
{
Console.WriteLine(product);
}