Ｃ＃Extension Methods 扩展方法使用

对已知类的方法进行扩展

一、已知类

public class ShoppingCart : IEnumerable<Product> {

public List<Product> Products { get; set; }

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

IEnumerator IEnumerable.GetEnumerator() {
return GetEnumerator();
}
}二、方法扩展

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 categoryParam) {

foreach (Product prod in productEnum) {
if (prod.Category == categoryParam) {
yield return prod;
}
}
}
}

三、实际使用

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 = products.FilterByCategory("Soccer").TotalPrices();