使用扩展方法(Chapter3 P39-41)

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

假设无法修改上面的类，这时可以使用扩展方法获得所需功能

namespace LanguageFeatures
{
    public static class MyExtensionMethods
    {
        public static decimal TotalPrices(this ShoppingCart cartParam)//this 关键字将TotalPrices标注为扩展方法。
        {
            decimal total = ;
            foreach (Product prod in cartParam.Products)
            {
                total += prod.Price;
            }
            return total;
        }
    }
}

使用扩展方法

namespace LanguageFeatures
{
public partial class Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}

protected string GetMessage()
{

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=19.5M},
new Product {Name ="Corner flag",Price=34.95M}

}
};
decimal cartTotal = cart.TotalPrices();
return String.Format("Total:{0:c}", cartTotal);
}
}
}