C#项目中常用到的设计模式

亦凉 2022-09-21 14:24 161阅读 0赞

## 1.引言 ##

一个项目的通常都是从Demo开始，不断为项目添加新的功能以及重构，也许刚开始的时候代码显得非常凌乱，毫无设计可言。但是随着项目的迭代，往往需要将很多相同功能的代码抽取出来，这也是设计模式的开始。熟练运用设计模式应该是每一个软件开发人员的必备技能。今天给大家介绍几个常用的设计模式。

##     ##

## 2. 单例模式 ##

单例模式恐怕是很多开发人员最先接触到的模式之一，可以认为就是一个全局变量。它的初始化过程无非就是一开始就new 一个instance，或者惰性初始化等需要用到的时候new 一个instance。这里需要注意的是在多线程情况下new一个instance。通常加上lock 可以解决问题。这里我们利用C\# 的系统函数 Interlocked.CompareExchange

> internal**class**SingletonOne
> 
>     \{ 
> 
>         privatestaticSingletonOne \_singleton;
> 
>         privateSingletonOne()
> 
>         \{ 
> 
>         \}
> 
>  
> 
>         publicstaticSingletonOneInstance
> 
>         \{ 
> 
>             **get**
> 
>             \{ 
> 
>                 **if**(\_singleton == **null**)
> 
>                 \{ 
> 
>                     Interlocked.CompareExchange(ref\_singleton,**new**SingletonOne(),**null**);
> 
>                 \}
> 
>  
> 
>                 **return**\_singleton;
> 
>             \}
> 
>         \}
> 
>     \}

## 3. 迭代器模式 ##

迭代器模式也是用的比较多的一种，通常见于C\#的内置容器数据结构 List，Stack等等，为了便于遍历容器内元素。这里给出一个简单版的Stack实现

>  internal**class**Stack : IEnumerable,IEnumerable
> 
>     \{ 
> 
>         privateT\[\]\_array;
> 
>         private**int**\_index;
> 
>         privateconst**int**DefaultSize = 4;
> 
>  
> 
>         publicStack(**int**size)
> 
>         \{ 
> 
>             **var**sized = size > 0?size : DefaultSize;
> 
>             **this**.\_array = **new**T\[sized\];
> 
>             **this**.\_index = 0;
> 
>         \}
> 
>  
> 
>         public**int**Count
> 
>         \{ 
> 
>             **get**\{ **return****this**.\_index;\}
> 
>         \}
> 
>  
> 
>         publicStack(IEnumerable data) : **this**(0)
> 
>         \{ 
> 
>             **var**enumrator = data.GetEnumerator();
> 
>             **while**(enumrator.MoveNext())
> 
>             \{ 
> 
>                 **var**item = enumrator.Current;
> 
>                 **this**.Push(item);
> 
>             \}
> 
>         \}
> 
>  
> 
>         public**void**Push(Titem)
> 
>         \{ 
> 
>             **if**(**this**.\_index **this**.\_array.Length)
> 
>             \{ 
> 
>                 **this**.\_array\[**this**.\_index\++\] = item;
> 
>             \}
> 
>             **else**
> 
>             \{ 
> 
>                 **var**newLength = **this**.\_array.Length1;
> 
>                 T\[\]newArray = **new**T\[newLength\];
> 
>                 Array.Copy(**this**.\_array,newArray,**this**.Count);
> 
>  
> 
>                 **this**.\_array = newArray;
> 
>                 **this**.Push(item);
> 
>             \}
> 
>         \}
> 
>  
> 
>         publicTPop()
> 
>         \{ 
> 
>             **if**(**this**.Count0)
> 
>             \{ 
> 
>                 **throw****new**ArgumentOutOfRangeException("pop");
> 
>             \}
> 
>             **else**
> 
>             \{ 
> 
>                 **this**.\_array\[**this**.\_index\] = **default**(T);
> 
>                 **return****this**.\_array\[\--**this**.\_index\];
> 
>             \}
> 
>         \}
> 
>  
> 
>         publicT**Get**(**int**index)
> 
>         \{ 
> 
>             **if**(**this**.Count  index)
> 
>             \{ 
> 
>                 **throw****new**ArgumentOutOfRangeException("Get");
> 
>             \}
> 
>             **else**
> 
>             \{ 
> 
>                 **return****this**.\_array\[index\];
> 
>             \}
> 
>         \}
> 
>  
> 
>         IEnumerator IEnumerable.GetEnumerator()
> 
>         \{ 
> 
>             **return****this**.GetEnumerator();
> 
>         \}
> 
>  
> 
>         publicIEnumerator GetEnumerator()
> 
>         \{ 
> 
>             **return****new**StackEnumerator(**this**);
> 
>         \}
> 
>     \}

Stack 的 迭代器内部实现：

>   
> 
> 
>  internal**class**StackEnumerator : IEnumerator,IEnumerator
> 
>     \{ 
> 
>         privateStack \_stack;
> 
>         private**int**\_index;
> 
>  
> 
>         publicStackEnumerator(Stack stack)
> 
>         \{ 
> 
>             **this**.\_stack = stack;
> 
>             **this**.\_index = -1;
> 
>         \}
> 
>  
> 
>         public**bool**MoveNext()
> 
>         \{ 
> 
>             **this**.\_index\++;
> 
>             **return****this**.\_index **this**.\_stack.Count;
> 
>         \}
> 
>  
> 
>         public**void**Reset()
> 
>         \{ 
> 
>             **this**.\_index = -1;
> 
>         \}
> 
>  
> 
>         **object**  IEnumerator.Current
> 
>         \{ 
> 
>             **get**\{ **return****this**.Current;\}
> 
>         \}
> 
>  
> 
>         publicTCurrent
> 
>         \{ 
> 
>             **get**\{ **return****this**.\_stack.**Get**(**this**.\_index);\}
> 
>         \}
> 
>  
> 
>         public**void**Dispose()
> 
>         \{ 
> 
>             **this**.\_stack = **null**;
> 
>         \}
> 
>     \}

## 4 工厂模式 ##

工厂模式细分的话有简单工厂模式、抽象工厂模式等。它最核心的就是如何通过 Factory new 一个 对象出来。在ASP.NET MVC 消息处理实现过程中工厂模式运用的非常多。比如

在MVC中处理一个Request，其实就是调用Controller下的一个Action，这就需要从Url 和Route 中反射出Controller对象，内部由ControllerFactory创建。

![image][]

它的默认实现是：DefaultControllerFactory

![image][image 1]

另一个例子是ValueProviderFactory，它使得Controller 下的Action 能够接收到前端传回来的数据并实现模型绑定，是典型的抽象工厂实现。

![image][image 2]

##     ##

## 5. 订阅模式 ##

订阅模式在某些项目运用比较多，比如 Knockout 整个项目就是一个大的订阅模式的实现，但是它是用javascript编写的。还有像微博、微信公众号等等订阅模式通常少不了。

通常可以定义接口：

> internal**interface**ISubject
> 
>     \{ 
> 
>         IEnumerableObservers\{ **get**;\}
> 
>         **void**Notify();
> 
>         **void**AddObserver(IObserver observer);
> 
>         **void**RemoveObserver(IObserver observer);
> 
>     \}
> 
>  
> 
>     internal**interface**IObserver
> 
>     \{ 
> 
>         **void**ReceiveSubject(ISubject subject);
> 
>     \}

实现：

>  internal**class**AritcleObserver : IObserver
> 
>     \{ 
> 
>         public**void**ReceiveSubject(ISubject subject)
> 
>         \{ 
> 
>             *// receive the subject*
> 
>         \}
> 
>     \}
> 
>  
> 
>     **class**WeChatArticle : ISubject
> 
>     \{ 
> 
>         privateICollection \_observers;
> 
>         private**string**\_name;
> 
>  
> 
>         publicWeChatArticle(**string**name)
> 
>         \{ 
> 
>             **this**.\_name = name;
> 
>             **this**.\_observers = **new**List();
> 
>         \}
> 
>  
> 
>         publicIEnumerableObservers
> 
>         \{ 
> 
>             **get**\{ **return****this**.\_observers;\}
> 
>         \}
> 
>  
> 
>         public**void**Notify()
> 
>         \{ 
> 
>             **foreach**(IObserver observer **in****this**.\_observers)
> 
>             \{ 
> 
>                 observer.ReceiveSubject(**this**);
> 
>             \}
> 
>         \}
> 
>  
> 
>         public**void**AddObserver(IObserver observer)
> 
>         \{ 
> 
>             **this**.\_observers.Add(observer);
> 
>         \}
> 
>  
> 
>         public**void**RemoveObserver(IObserver observer)
> 
>         \{ 
> 
>             **this**.\_observers.Remove(observer);
> 
>         \}
> 
>     \}

## 6.  责任链模式 ##

责任链模式没有像工厂模式那样被人熟悉，在ASP.NET WebApi 中有一个非常典型的实现 就是WebApi的消息处理管道HttpMessageHandler

![image][image 3]

这里给一个简单的模拟

>  **class**DataRequest
> 
>     \{ 
> 
>         public**string**FileName\{ **get**;**set**;\}
> 
>     \}
> 
>  
> 
>     **class**DataResponse
> 
>     \{ 
> 
>         public**string**Error\{ **get**;**set**;\}
> 
>         public**string**Data\{ **get**;**set**;\}
> 
>     \}
> 
>  
> 
>     internalabstract**class**RequestHandler
> 
>     \{ 
> 
>         publicRequestHandlerNextHandler\{ **get**;**set**;\}
> 
>         publicabstractDataResponse Process(DataRequest request);
> 
>     \}
> 
>  
> 
>     **class**ReadRequestHandler : RequestHandler
> 
>     \{ 
> 
>         publicoverrideDataResponse Process(DataRequest request)
> 
>         \{ 
> 
>             **return****new**DataResponse()
> 
>             \{ 
> 
>                 Data = File.ReadAllText(request.FileName)
> 
>             \};
> 
>         \}
> 
>     \}
> 
>  
> 
>     **class**ExistsRequestHandler : RequestHandler
> 
>     \{ 
> 
>         publicoverrideDataResponse Process(DataRequest request)
> 
>         \{ 
> 
>             **if**(File.Exists(request.FileName))
> 
>             \{ 
> 
>                 **return****this**.NextHandler.Process(request);
> 
>             \}
> 
>             **else**
> 
>             \{ 
> 
>                 **return****new**DataResponse()
> 
>                 \{ 
> 
>                     Error = "no exists"
> 
>                 \};
> 
>             \}
> 
>         \}
> 
>     \}

## 7. 组合模式 ##

组合模式是使得单个对象和组合对象有一致的行为，一致的行为可以理解为拥有同一个接口，比如图形显示

> **class**ControlContext
> 
>     \{ 
> 
>     \}
> 
>  
> 
>     internal**interface**IControl
> 
>     \{ 
> 
>         **void**Draw(ControlContext context);
> 
>     \}
> 
>  
> 
>     **class**Line : IControl
> 
>     \{ 
> 
>         public**void**Draw(ControlContext context)
> 
>         \{ 
> 
>         \}
> 
>     \}
> 
>  
> 
>     **class**Circle : IControl
> 
>     \{ 
> 
>         public**void**Draw(ControlContext context)
> 
>         \{\}
> 
>     \}
> 
>  
> 
>     **class**CompositeControl : IControl
> 
>     \{ 
> 
>         privateList controls;
> 
>  
> 
>         publicCompositeControl(IList cons)
> 
>         \{ 
> 
>             **this**.controls = **new**List(cons);
> 
>         \}
> 
>  
> 
>         public**void**Draw(ControlContext context)
> 
>         \{ 
> 
>             **this**.controls.**ForEach**(c => c.Draw(context));
> 
>         \}
> 
>  
> 
>         public**void**Add(IControl control)
> 
>         \{ 
> 
>             **this**.controls.Add(control);
> 
>         \}
> 
>     \}

## 8. 总结 ##

市场上有很多关于设计模式的书，但是基本的设计模式大概有20多种，本文给大家介绍了几种项目中常见的设计模式，其实有些设计模式在实际项目已经不知不觉用起来了。

[image]: /images/20220721/e87caa134ded4ee88435db280dba0fc1.png
[image 1]: /images/20220721/05ab00f3b717480fb25c5bb2862d2b72.png
[image 2]: /images/20220721/9e117740bb1f460ba168c4b2fe99b221.png
[image 3]: /images/20220721/a85117c3521e4edaa1914d987e68c1b3.png