Unity 学习笔记(1) -- Unity简介及简单使用

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Unity是微软Patterns & Practices团队所开发的一个轻量级的，并且可扩展的依赖注入(Dependency Injection)容器，它支持常用的三种依赖注入方式：构造器注入(Constructor Injection)、属性注入(Property Injection)，以及方法调用注入(Method Call Injection).现在Unity最新的版本的1.2版，可以在微软的开源站点http://unity.codeplex.com下载最新的发布版本和文档。通过使用Unity，我们能轻松构建松耦合结构的程序，从而让整个程序框架变得清晰和易于维护。

在平常的软件编码过程中，程序的逻辑往往很复杂，尤其是大型项目的开发中，一个模块常常会去引用其他的模块，假设我们有一个监控器类，用来监控CPU的温度，当温度达到预警的范围时，监控器有一个报警的方法，方法里面通过短信提醒器，以发送短信的方式通知维护人员。于是就出现了下面这样一段最为常见的代码：

<span class="lnum">   1:  </span><span class="kwrd">public</span> <span class="kwrd">class</span> Monitor




<span class="lnum">   2:  </span>{




<span class="lnum">   3:  </span>       <span class="kwrd">public</span> <span class="kwrd">void</span> Alarm()




<span class="lnum">   4:  </span>       {




<span class="lnum">   5:  </span>               SMSNotify notify = <span class="kwrd">new</span> SMSNotify();




<span class="lnum">   6:  </span>               notify.Send();




<span class="lnum">   7:  </span>        }




<span class="lnum">   8:  </span>}

在Monitor类中，直接引用到了一个短信提醒器的类，这是最为不灵活和最不易于扩展的一种方式。或许我们想到了面向接口编程，利用多态的好处，可以提供灵活的不同子类的实现，增加代码扩展性等等。但是说到底，接口一定是需要实现的，也就是如下语句迟早要执行：

<span class="lnum">   1:  </span><span class="kwrd">public</span> <span class="kwrd">void</span> Alarm()




<span class="lnum">   2:  </span>{




<span class="lnum">   3:  </span>       INotify notify = <span class="kwrd">new</span> SMSNotify();




<span class="lnum">   4:  </span>       notify.Send();




<span class="lnum">   5:  </span>}

这样看来，在实现INotify这个接口的时候，仍然需要具体的类来实现，而这样的代码在程序编译的时候就已经固定下来，如果以后需要使用新的提醒器，仍旧需要修改源代码并重新编译。并且在我们的Monitor类中，明显依赖SMSNotify类，二者之间的耦合度非常紧密。因此Ioc(控制反转)模式被提出用来解决这种问题，也即把接口的具体实现延缓到运行时，接口的实现类是在运行时被装载的。这样，就算有了新的实现类，也不需要更改调用者的代码(可以在Unity中使用配置文件的方式实现)。这种Ioc模式可以被形象的比喻为：接口就像一个空壳，而在具体实现时，向这个空壳注入内容，而让它成为一个真正的实体。这种模式也被形象的称为：依赖注入。通过使用Unity，我们能构建松耦合的软件，并且对象之间相互关联的细节，我们也不必关心，可以交由依赖注入容器全权负责。

前面也提到了依赖注入常用的三种形式：构造器注入、属性注入和方法调用注入，我们可以通过例子来实现这三种形式的注入。还是以上面的场景为例，我们的几个类和接口如下图：

1

1.Constructor Injection

IMonitor接口定义：

<span class="lnum">   1:  </span><span class="kwrd">public</span> <span class="kwrd">interface</span> IMonitor




<span class="lnum">   2:  </span>{




<span class="lnum">   3:  </span>    <span class="kwrd">void</span> Alarm();




<span class="lnum">   4:  </span>}

Monitor类：

<span class="lnum">   1:  </span><span class="kwrd">public</span> <span class="kwrd">class</span> Monitor : IMonitor




<span class="lnum">   2:  </span>{




<span class="lnum">   3:  </span>    <span class="kwrd">private</span> INotify notify;




<span class="lnum">   4:  </span>




<span class="lnum">   5:  </span>    <span class="kwrd">public</span> Monitor(INotify n)




<span class="lnum">   6:  </span>    {




<span class="lnum">   7:  </span>        notify = n;




<span class="lnum">   8:  </span>    }




<span class="lnum">   9:  </span>




<span class="lnum">  10:  </span>    <span class="kwrd">public</span> <span class="kwrd">void</span> Alarm()




<span class="lnum">  11:  </span>    {




<span class="lnum">  12:  </span>        notify.Send();




<span class="lnum">  13:  </span>    }




<span class="lnum">  14:  </span>}

INotify接口定义：

<span class="lnum">   1:  </span><span class="kwrd">public</span> <span class="kwrd">interface</span> INotify




<span class="lnum">   2:  </span>{




<span class="lnum">   3:  </span>    <span class="kwrd">void</span> Send();




<span class="lnum">   4:  </span>}

EmailNotify类：

<span class="lnum">   1:  </span><span class="kwrd">public</span> <span class="kwrd">class</span> EmailNotify : INotify




<span class="lnum">   2:  </span>{




<span class="lnum">   3:  </span>    <span class="kwrd">public</span> <span class="kwrd">void</span> Send()




<span class="lnum">   4:  </span>    {




<span class="lnum">   5:  </span>        Console.WriteLine(<span class="str">"Send Email Notify..."</span>);




<span class="lnum">   6:  </span>    }




<span class="lnum">   7:  </span>}

SMSNotify类：

<span class="lnum">   1:  </span><span class="kwrd">public</span> <span class="kwrd">class</span> SMSNotify : INotify




<span class="lnum">   2:  </span>{




<span class="lnum">   3:  </span>    <span class="kwrd">public</span> <span class="kwrd">void</span> Send()




<span class="lnum">   4:  </span>    {




<span class="lnum">   5:  </span>        Console.WriteLine(<span class="str">"Send SMS Notify..."</span>);




<span class="lnum">   6:  </span>    }




<span class="lnum">   7:  </span>}

可以看到，在Monitor类的构造函数里面，传入的参数是一个INotify接口类型，Alarm方法，调用了实现类的Send方法，但具体调用哪一个实现类的Send方法，只有在注入实体后才知道。Unity容器中，通常使用RegisterType和Resolve方法来分别注册和获取实例，并且这两个方法有很多泛型和非泛型的重载，具体的类型和参数，可以参考Unity的官方帮助文档。

现在我们向Monitor的构造函数注入实现INotify接口的实例:

<span class="lnum">   1:  </span><span class="kwrd">static</span> <span class="kwrd">void</span> Main(<span class="kwrd">string</span>[] args)




<span class="lnum">   2:  </span>{




<span class="lnum">   3:  </span>    IUnityContainer container = <span class="kwrd">new</span> UnityContainer();




<span class="lnum">   4:  </span>    container.RegisterType<IMonitor, Monitor>().RegisterType<INotify, SMSNotify>();




<span class="lnum">   5:  </span>




<span class="lnum">   6:  </span>    IMonitor monitor = container.Resolve<IMonitor>();




<span class="lnum">   7:  </span>    monitor.Alarm();




<span class="lnum">   8:  </span>




<span class="lnum">   9:  </span>    Console.ReadLine();




<span class="lnum">  10:  </span>}

代码中我们注入的INotify实例是SMSNotify类的实例，然后调用monitor.Alrarm()，里面会调用notify.Send(). 运行查看结果： 2上面是针对单个构造函数的情况，如果有多个构造函数，需要指明哪个构造函数是需要被注入的,也即需要在指定被注入的构造函数加上attribute:InjectionConstructor

<span class="lnum">   1:  </span><span class="kwrd">public</span> Monitor(INotify n, <span class="kwrd">string</span> name)




<span class="lnum">   2:  </span>{




<span class="lnum">   3:  </span>    notify = n;




<span class="lnum">   4:  </span>}




<span class="lnum">   5:  </span>




<span class="lnum">   6:  </span>[InjectionConstructor]




<span class="lnum">   7:  </span><span class="kwrd">public</span> Monitor(INotify n)




<span class="lnum">   8:  </span>{




<span class="lnum">   9:  </span>    notify = n;




<span class="lnum">  10:  </span>}

运行后可得到一样的结果.

2.Property Injection

通过属性注入，我们需要加上attribute: Dependency，使得Unity容器在获取类对象实例时，自动实例化该属性所依赖的对象，并注入到属性中。

修改Monitor类,实现下面的代码：

<span class="lnum">   1:  </span><span class="kwrd">public</span> <span class="kwrd">class</span> Monitor : IMonitor




<span class="lnum">   2:  </span>{




<span class="lnum">   3:  </span>    [Dependency]




<span class="lnum">   4:  </span>    <span class="kwrd">public</span> INotify Notify { get; set; }




<span class="lnum">   5:  </span>




<span class="lnum">   6:  </span>    <span class="kwrd">public</span> <span class="kwrd">void</span> Alarm()




<span class="lnum">   7:  </span>    {




<span class="lnum">   8:  </span>        Notify.Send();




<span class="lnum">   9:  </span>    }




<span class="lnum">  10:  </span>}

再在Main函数里面，修改原有的代码，这次我们让容器注入EmailNotify实例：

<span class="lnum">   1:  </span>container.RegisterType<INotify, EmailNotify>();

运行查看结果： 3还有一个比较方便的地方，可以为Dependency特性指定名称，这样，在注入时，会将RegisterType所指定的对应名称的实体进行注入，例如：

<span class="lnum">   1:  </span>    <span class="kwrd">public</span> <span class="kwrd">class</span> Monitor : IMonitor




<span class="lnum">   2:  </span>    {




<span class="lnum">   3:  </span>        [Dependency(<span class="str">"SMS"</span>)]




<span class="lnum">   4:  </span>        <span class="kwrd">public</span> INotify Notify { get; set; }




<span class="lnum">   5:  </span>




<span class="lnum">   6:  </span>        <span class="kwrd">public</span> <span class="kwrd">void</span> Alarm()




<span class="lnum">   7:  </span>        {




<span class="lnum">   8:  </span>            Notify.Send();




<span class="lnum">   9:  </span>        }




<span class="lnum">  10:  </span>    }

修改Main函数，在RegisterType函数中指定注入名称:

<span class="lnum">   1:  </span>            container.RegisterType<INotify, EmailNotify>(<span class="str">"Email"</span>);




<span class="lnum">   2:  </span>            container.RegisterType<INotify, SMSNotify>(<span class="str">"SMS"</span>);

运行查看结果： 2

3.Method Call Injection

Method Call Injection注入的时机和Constructor Injection有一定的区别，构造函数注入，是在容器创建实例的时候，而方法调用注入，是在方法被调用的时候。实现方法调用注入，需要在指定注入的方法前加上attribute: InjectionMethod

修改Monitor类的代码如下：

<span class="lnum">   1:  </span>    <span class="kwrd">public</span> <span class="kwrd">class</span> Monitor : IMonitor




<span class="lnum">   2:  </span>    {




<span class="lnum">   3:  </span>        <span class="kwrd">private</span> INotify notify;




<span class="lnum">   4:  </span>




<span class="lnum">   5:  </span>        [InjectionMethod]




<span class="lnum">   6:  </span>        <span class="kwrd">public</span> <span class="kwrd">void</span> GetNotify(INotify n)




<span class="lnum">   7:  </span>        {




<span class="lnum">   8:  </span>            notify = n;




<span class="lnum">   9:  </span>        }




<span class="lnum">  10:  </span>




<span class="lnum">  11:  </span>        <span class="kwrd">public</span> <span class="kwrd">void</span> Alarm()




<span class="lnum">  12:  </span>        {




<span class="lnum">  13:  </span>            notify.Send();




<span class="lnum">  14:  </span>        }




<span class="lnum">  15:  </span>    }

在程序运行时，容器会自动实例化GetNotify方法所依赖的对象，并自动调用该方法，将其注入到方法中。

Main函数如下：

<span class="lnum">   1:  </span>        <span class="kwrd">static</span> <span class="kwrd">void</span> Main(<span class="kwrd">string</span>[] args)




<span class="lnum">   2:  </span>        {




<span class="lnum">   3:  </span>            IUnityContainer container = <span class="kwrd">new</span> UnityContainer();




<span class="lnum">   4:  </span>            container.RegisterType<IMonitor, Monitor>();




<span class="lnum">   5:  </span>            container.RegisterType<INotify, EmailNotify>();




<span class="lnum">   6:  </span>




<span class="lnum">   7:  </span>            IMonitor monitor = container.Resolve<IMonitor>();




<span class="lnum">   8:  </span>            monitor.Alarm();




<span class="lnum">   9:  </span>




<span class="lnum">  10:  </span>            Console.ReadLine();




<span class="lnum">  11:  </span>        }

运行查看结果：

3

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