c# 链式编程

goodwangLib 2018-02-15

展开全文

先写一段代码，让大家了解或重温一下什么是链式编程：

C#代码

///
/// EntityFramwork中的链式编程示例
///
private void Example1()
{
using (NorthwindEFEntities northwindEFEntities = new NorthwindEFEntities())
{
northwindEFEntities.Employees
.Where(e => e.FirstName.StartsWith('C'))
.Select(e => e.FirstName)
.OrderBy(s => s);
}
}

///

/// EntityFramwork中的链式编程示例 ///

private void Example1() { using (NorthwindEFEntities northwindEFEntities = new NorthwindEFEntities()) { northwindEFEntities.Employees .Where(e => e.FirstName.StartsWith('C')) .Select(e => e.FirstName) .OrderBy(s => s); } }

这一个基本的查询，执行了三个操作：1.查找FristName以C开头的员工；2.取员工的FirstName；3.将名字排序。

EF中只需要一个语句，通过.将三者链成一个语句。后面还可以链接更多的语句，如果需要。
下面代码作一些演化：

C#代码

///
/// 链式编程示例2
///
private static void Example2()
{
Person person = new Person { Name = 'Tom' }
.Run()
.Sing()
.Swim();
}
class Person
{
public string Name { get; set; }
public Person Run()
{
Console.WriteLine('Run');
return this;
}
public Person Swim()
{
Console.WriteLine('Swim');
return this;
}
public Person Sing()
{
Console.WriteLine('Sing');
return this;
}
}

///

/// 链式编程示例2 ///

private static void Example2() { Person person = new Person { Name = 'Tom' } .Run() .Sing() .Swim(); } class Person { public string Name { get; set; } public Person Run() { Console.WriteLine('Run'); return this; } public Person Swim() { Console.WriteLine('Swim'); return this; } public Person Sing() { Console.WriteLine('Sing'); return this; } }

这段代码定义了Peoson类，有三个操作Run、Swim、Sing，操作完成后返回自身this（有返回值是链式编程的关键）。返回自身this好比说执行完操作先别走人，还（可能）有其它操作要去做，如Example2中：先造一个People，先命令ta跑步，跑完先别休息再唱歌，再游泳，游泳完OK了。

链式编程是将多个操作（多行代码）通过点号'.'链接在一起成为一句代码。(定义不严密，表达能力好的请给修正一下)
以下为常规代码与链式代码的比较：

C#代码

///
/// 链式编程示例3 对比
///
private void Example3()
{
//链式代码
Person person = new Person { Name = 'Tom' }
.Run()
.Sing()
.Swim()
.Run()
.Sing()
.Swim();
//常规代码
Person person2 = new Person();
person2.Run();
person2.Sing();
person2.Swim();
person2.Run();
person2.Sing();
person2.Swim();
}

///

/// 链式编程示例3 对比 ///

private void Example3() { //链式代码 Person person = new Person { Name = 'Tom' } .Run() .Sing() .Swim() .Run() .Sing() .Swim(); //常规代码 Person person2 = new Person(); person2.Run(); person2.Sing(); person2.Swim(); person2.Run(); person2.Sing(); person2.Swim(); }

为了增强效果，都执行了两轮操作。个人感觉链式代码更加精炼简洁易读。

链式代码要求操作有返回值，但对于很多操作大都是void型，什么也不返回，这样就很难链起来了。当然也有解决办法，可能不太优雅。
本人使用扩展方法解决这个问题，首先引入一个泛型扩展：

C#代码

///
/// 先执行操作，再返回自身
///
public static T Do(this T t, Action action)
{
action(t);
return t;
}

///

/// 先执行操作，再返回自身 ///

public static T Do(this T t, Action action) { action(t); return t; }

下面是调用示例，其中Student类操作都是void型的。

C#代码

///
/// 链式编程示例4
///
private static void Example4()
{
new Student { Name = 'Tom' }
.Do(s => s.Run())
.Do(s => s.Sing())
.Do(s => s.Sing())
.Do(s => s.Name = 'Bob');
}
public class Student
{
public string Name { get; set; }
public void Run() { Console.WriteLine('Run'); }
public void Swim() { Console.WriteLine('Swim'); }
public void Sing() { Console.WriteLine('Sing'); }
}

///

/// 链式编程示例4 ///

private static void Example4() { new Student { Name = 'Tom' } .Do(s => s.Run()) .Do(s => s.Sing()) .Do(s => s.Sing()) .Do(s => s.Name = 'Bob'); } public class Student { public string Name { get; set; } public void Run() { Console.WriteLine('Run'); } public void Swim() { Console.WriteLine('Swim'); } public void Sing() { Console.WriteLine('Sing'); } }