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       通过昨天的例子可以看到泛型类型实现IAccount接口的要求过于严厉。为了将Accumulate()方法改为泛型方法，还要去创建一个IAccount接口，然后让Account类继承IAccount接口，然后....杯具( ⊙ o ⊙ )啊！ 在今天的例子中，我们可以创建独立于任何接口的泛型方法。这个就需要泛型委托机制来帮忙实现了。

 下面是修改后的泛型委托的例子

using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
using System.Text;namespace GenericMethod
{// 定义一个泛型委托// TInput是要累加的对象// TSummary是返回类型public delegate TSummary Action<TInput, TSummary>(TInput t, TSummary u);public class Account{private string name;public string Name{get{return name;}            }private decimal balance;public decimal Balance{get{return balance;}}public Account(string name, decimal balance){this.name = name;this.balance = balance;}        }public static class Algorithm{// 使用委托的泛型方法public static TSummary Accumulate<TInput, TSummary>(IEnumerable<TInput> coll, Action<TInput, TSummary> action){TSummary sum = default(TSummary);foreach (TInput input in coll){sum = action(input, sum);}return sum;}}class Program{static void Main(string[] args){List<Account> accounts = new List<Account>();accounts.Add(new Account("Christian", 1500));accounts.Add(new Account("Sharon", 2200));accounts.Add(new Account("Katie", 1800));// 通过匿名方法调用//decimal amount = Algorithm.Accumulate<Account, decimal>(accounts, delegate(Account a, decimal d){return a.Balance + d;});// 还可以通过λ表达式调用decimal amount = Algorithm.Accumulate<Account, decimal>(accounts, (a, d) => a.Balance + d;);Console.WriteLine(amount.ToString());Console.ReadLine();}}
}

 

 

郁闷了，编译有个错误：

Error 1 ) expected E:\C Sharp\ComputerManager\GenericMethod\GenericMethod\Program.cs 70 102 GenericMethod
Error 2 Invalid expression term ')' E:\C Sharp\ComputerManager\GenericMethod\GenericMethod\Program.cs 70 103 GenericMethod
Error 3 Only assignment, call, increment, decrement, and new object expressions can be used as a statement E:\C Sharp\ComputerManager\GenericMethod\GenericMethod\Program.cs 70 102 GenericMethod

编译怎么出问题了，实在不解，待会儿查下。

NOTE：偶晕倒，原来是这里出问题了

 decimal amount = Algorithm.Accumulate<Account, decimal>(accounts, (a, d) => a.Balance + d;);

应该是这样写，多了一个分号囧

 decimal amount = Algorithm.Accumulate<Account, decimal>(accounts, (a, d) => a.Balance + d);

 

通过匿名方法调用的那个是没有任何问题的。

 

下面的这个就是标准的委托形式了，这个看不懂，就要回去看下委托的章节了。

using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
using System.Text;namespace GenericMethod
{// 定义一个泛型委托// TInput是要累加的对象// TSummary是返回类型public delegate TSummary Action<TInput, TSummary>(TInput t, TSummary u);public class Account{private string name;public string Name{get{return name;}            }private decimal balance;public decimal Balance{get{return balance;}}public Account(string name, decimal balance){this.name = name;this.balance = balance;}        }public static class Algorithm{// 使用委托的泛型方法public static TSummary Accumulate<TInput, TSummary>(IEnumerable<TInput> coll, Action<TInput, TSummary> action){TSummary sum = default(TSummary);foreach (TInput input in coll){sum = action(input, sum);}return sum;}public static decimal AccountAdder(Account a, decimal d){return a.Balance + d;}}class Program{static void Main(string[] args){List<Account> accounts = new List<Account>();accounts.Add(new Account("Christian", 1500));accounts.Add(new Account("Sharon", 2200));accounts.Add(new Account("Katie", 1800));// 通过匿名方法调用//decimal amount = Algorithm.Accumulate<Account, decimal>(accounts, delegate(Account a, decimal d){return a.Balance + d;});// 还可以通过λ表达式调用//decimal amount = Algorithm.Accumulate<Account, decimal>(accounts, (a, d) => a.Balance + d;);// 使用标准的委托形式// 单独再写一个AccountAdder方法decimal amount = Algorithm.Accumulate<Account, decimal>(accounts, Algorithm.AccountAdder);Console.WriteLine(amount.ToString());Console.ReadLine();}}
}

 

这样就很灵活了，你可以在Action方法里面想做什么就做什么，可以乘法除法都可以了。

 

下面再做一个扩展可以在Accumulate的时候加入一个委托应用来检查某个账目是否应累加进去。

using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
using System.Text;namespace GenericMethod
{// 定义一个泛型委托// TInput是要累加的对象// TSummary是返回类型public delegate TSummary Action<TInput, TSummary>(TInput t, TSummary u);public class Account{private string name;public string Name{get{return name;}            }private decimal balance;public decimal Balance{get{return balance;}}public Account(string name, decimal balance){this.name = name;this.balance = balance;}        }public static class Algorithm{// 使用委托的泛型方法public static TSummary Accumulate<TInput, TSummary>(IEnumerable<TInput> coll, Action<TInput, TSummary> action){TSummary sum = default(TSummary);foreach (TInput input in coll){sum = action(input, sum);}return sum;}public static decimal AccountAdder(Account a, decimal d){return a.Balance + d;}public static TSummary AccumulateIf<TInput, TSummary>(IEnumerable<TInput> coll, Action<TInput, TSummary> action, Predicate<TInput> match){TSummary sum = default(TSummary);foreach (TInput a in coll){if (match(a)){sum = action(a, sum);}}return sum;}}class Program{static void Main(string[] args){List<Account> accounts = new List<Account>();accounts.Add(new Account("Christian", 1500));accounts.Add(new Account("Sharon", 2200));accounts.Add(new Account("Katie", 1800));// 通过匿名方法调用//decimal amount = Algorithm.Accumulate<Account, decimal>(accounts, delegate(Account a, decimal d){return a.Balance + d;});// 还可以通过λ表达式调用//decimal amount = Algorithm.Accumulate<Account, decimal>(accounts, (a, d) => a.Balance + d);// 使用标准的委托形式// 单独再写一个AccountAdder方法// decimal amount = Algorithm.Accumulate<Account, decimal>(accounts, Algorithm.AccountAdder);// 新委托方法的调用decimal amount = Algorithm.AccumulateIf<Account, decimal>(accounts, (a, d) => a.Balance + d, a => a.Balance > 2000);Console.WriteLine(amount.ToString());Console.ReadLine();}}
}

 对Array类使用泛型方法

using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
using System.Text;namespace ArrayGenericDelegate
{public class Person{private string firstName;public string FirstName{get{return firstName;}            }private string lastName;public string LastName{get{return lastName;}}public Person(string firstname, string lastname){this.firstName = firstname;this.lastName = lastname;}}public class Racer{public string Name{get;set;}public string Team{get;set;}public Racer(string name){this.Name = name;}}class Program{static void Main(string[] args){Person[] persons = {new Person("Emerson", "Fittipaldi"),new Person("Niki", "Lauda"),new Person("Ayrton", "Senda"),new Person("Michael", "Schumacher")};// 调用Array的Sort泛型方法给Person数组进行首姓名排序Array.Sort(persons, (p1, p2) => p1.FirstName.CompareTo(p2.FirstName));// 调用Array的Foreach泛型方法将Person数组的首姓名输出到控制台Array.ForEach(persons, p => Console.WriteLine("{0}", p.FirstName));// 调用Array的Foreach泛型方法将Person数组的末姓名输出到控制台Array.ForEach(persons, p => Console.WriteLine("{0}", p.LastName));// 调用Array的FindAll泛型方法查找首字母以S开头的Person类集合Person[] sPersons = Array.FindAll(persons, p => p.LastName.StartsWith("S"));// 调用Array的ConvetAll泛型方法将一种类型数组转换为另一种类型数组Racer[] racers = Array.ConvertAll<Person, Racer>(persons, p => new Racer(String.Format("{0} {1}", p.FirstName, p.LastName)));Console.ReadLine();}}
}

从上面的例子看出Array类的泛型方法还是很强大的。