【读书笔记】 泛型委托
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。