Unity 配置：typeConverter的使用

本文主要介绍自己在使用Unity时碰到的一个问题，及解决方案。
由于本人不擅长写作，所以文字都很简单，各位还是主要看代码及DEMO吧。

首先先看一下以下代码：

     public   interface  ILogger
     {
        void Write();
    }

     public   class  FlatFileLogger : ILogger
     {
        private Message _message;
        public FlatFileLogger(Message message)
        {
            _message = message;
        }

        public void Write()
        {
            Console.WriteLine(String.Format("Message:{0}", _message));
            Console.WriteLine("Target:FlatFile");
        }
    }

     public   class  Message
     {
        private string _message;
        private Message(string message)
        {
            _message = message;
        }

        public override string ToString()
        {
            return _message.ToString();
        }

        public static Message CreateMessage(string message)
        {
            return new Message(message);
        }
    }

     class  Program
     {
        static void Main(string[] args)
        {
            IUnityContainer container = new UnityContainer();
            UnityConfigurationSection section = (UnityConfigurationSection)ConfigurationManager.GetSection("unity");
            section.Containers["containerOne"].Configure(container);

            ILogger log = container.Resolve<ILogger>();
            log.Write();

            Console.ReadLine();
        }
    }

配置文件：

<? xml version="1.0" encoding="utf-8"  ?>
< configuration >
     < configSections >
         < section  name ="unity"  type ="Microsoft.Practices.Unity.Configuration.UnityConfigurationSection,
                 Microsoft.Practices.Unity.Configuration, Version=1.0.0.0,
                 Culture=neutral, PublicKeyToken=31bf3856ad364e35"   />
     </ configSections >
     < unity >
         < typeAliases >
             < typeAlias  alias ="string"  type ="System.String, mscorlib"   />

             <!--  Lifetime manager types  -->
             < typeAlias  alias ="singleton"
                 type ="Microsoft.Practices.Unity.ContainerControlledLifetimeManager,
               Microsoft.Practices.Unity"   />
             < typeAlias  alias ="external"
                 type ="Microsoft.Practices.Unity.ExternallyControlledLifetimeManager,
               Microsoft.Practices.Unity"   />

             <!--  User-defined type aliases  -->
             < typeAlias  alias ="ILogger"  type ="UnityDemo.ILogger, UnityDemo"   />
             < typeAlias  alias ="FlatFileLogger"  type ="UnityDemo.FlatFileLogger, UnityDemo"   />
             < typeAlias  alias ="Message"  type ="UnityDemo.Message, UnityDemo"   />
         </ typeAliases >
         < containers >
             < container  name ="containerOne" >
                 < types >
                      < type  type ="ILogger"  mapTo ="FlatFileLogger"/ >
                 </ types >
             </ container >
         </ containers >
     </ unity >
</ configuration >

一运行程序就报错，那是因为Message类的构造函数是私有的，Unity无法自动装配。

本来父对象的构造函数如果需要指定具体值，可以通过修改配置文件来达到目的，配置修改如下：

< type  type ="ILogger"  mapTo ="FlatFileLogger" >
                         < typeConfig  extensionType ="Microsoft.Practices.Unity.Configuration.TypeInjectionElement,
                                     Microsoft.Practices.Unity.Configuration" >
                             < constructor >
                                 < param  name ="message"  parameterType ="Message" >
                                     < value  value ="Some Value" ></ value >
                                 </ param >
                             </ constructor >
                         </ typeConfig >
                     </ type >

但现在还有一个问题，就是由于参数message的类型是自定义类型，不是像string, int等系统类型， 按以上配置是无法把一个Message的实例传给FlatFileLogger的构造函数的。这时就需要用到typeConverter，把value中的值转换成一个Message的实例。

LoggerConverter：

    public   class  LoggerConverter : TypeConverter
     {
        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
        {
            if (sourceType == typeof(string))
            {
                return true;
            }
            return base.CanConvertFrom(context, sourceType);
        }

        public override object ConvertFrom(ITypeDescriptorContext context,
           CultureInfo culture, object value)
        {
            if (value is string)
            {
                return Message.CreateMessage(value.ToString());
            }
            return base.ConvertFrom(context, culture, value);
        }
    }

 修改后最终的配置文件：

<? xml version="1.0" encoding="utf-8"  ?>
< configuration >
     < configSections >
         < section  name ="unity"  type ="Microsoft.Practices.Unity.Configuration.UnityConfigurationSection,
                 Microsoft.Practices.Unity.Configuration, Version=1.0.0.0,
                 Culture=neutral, PublicKeyToken=31bf3856ad364e35"   />
     </ configSections >
     < unity >
         < typeAliases >
             < typeAlias  alias ="string"  type ="System.String, mscorlib"   />

             <!--  Lifetime manager types  -->
             < typeAlias  alias ="singleton"
                 type ="Microsoft.Practices.Unity.ContainerControlledLifetimeManager,
               Microsoft.Practices.Unity"   />
             < typeAlias  alias ="external"
                 type ="Microsoft.Practices.Unity.ExternallyControlledLifetimeManager,
               Microsoft.Practices.Unity"   />

             <!--  User-defined type aliases  -->
             < typeAlias  alias ="ILogger"  type ="UnityDemo.ILogger, UnityDemo"   />
             < typeAlias  alias ="FlatFileLogger"  type ="UnityDemo.FlatFileLogger, UnityDemo"   />
             < typeAlias  alias ="LoggerConverter"  type ="UnityDemo.LoggerConverter, UnityDemo"   />
             < typeAlias  alias ="Message"  type ="UnityDemo.Message, UnityDemo"   />
         </ typeAliases >
         < containers >
             < container  name ="containerOne" >
                 < types >
                      < type  type ="ILogger"  mapTo ="FlatFileLogger"  name ="FlatFileLogger"   />
                      < type  type ="ILogger"  mapTo ="DatabaseLogger"  name ="DatabaseLogger" />
                     
                      < type  type ="ILogger"  mapTo ="FlatFileLogger" >
                         < typeConfig  extensionType ="Microsoft.Practices.Unity.Configuration.TypeInjectionElement,
                                     Microsoft.Practices.Unity.Configuration" >
                             < constructor >
                                 < param  name ="message"  parameterType ="Message" >
                                     < value  value ="FlatFileLogger"  type ="Message"  typeConverter ="LoggerConverter" ></ value >
                                 </ param >
                             </ constructor >
                         </ typeConfig >
                     </ type >
                    
                 </ types >
             </ container >
         </ containers >
     </ unity >
</ configuration >

经过修改后，程序终于可以正常运行了。
运行结果：
 

本文代码