Unity中使用多构造函数

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我是靠谱客的博主花痴乐曲，最近开发中收集的这篇文章主要介绍Unity中使用多构造函数，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

如果要实例化的类只有一个构造函数, 则使用方法很简单使用方法如下:

 
          using (IUnityContainer container =  
          new 
          UnityContainer())  
         
          {  
         
          UnityConfigurationSection section = (UnityConfigurationSection)ConfigurationManager.GetSection( 
          "unity" 
          );  
         
          section.Configure(container);&nbsp;&nbsp;&nbsp;&nbsp; 
          //...  
         
          ILogger logger = container.Resolve<ILogger>( 
          "DatabaseLogger" 
          );  
         
          return 
          logger;  
         
          }

其中配置文件为

 
          <?xml version= 
          "1.0" 
          encoding= 
          "utf-8" 
          ?>  
         
          <configuration>  
         
          <configSections>  
         
          <section name= 
          "unity" 
          type= 
          "Microsoft.Practices.Unity.Configuration.UnityConfigurationSection,Microsoft.Practices.Unity.Configuration" 
          />  
         
          </configSections>  
         
          <unity>  
         
          <containers>  
         
          <container>  
         
          <types>  
         
          <type type= 
          "Bery.ILogger, UnityStudy" 
          mapTo= 
          "Bery.DatabaseLogger, UnityStudy" 
          name= 
          "DatabaseLogger" 
          >  
         
          </type>  
         
          </types>  
         
          </container>  
         
          </containers>  
         
          </unity>  
         
          </configuration>

如果DatabaseLogger类中的有两个构造函数, 代码如下

 
          public DatabaseLogger()  
         
          {   
         
          }  
         
          public DatabaseLogger(string name)  
         
          {  
         
          }

则Unity自动使用参数最多的构造函数进行创建对象, 会抛出以下异常:

 
     
          Microsoft.Practices.Unity.ResolutionFailedException: Resolution of the dependency failed, type =  
          "Bery.ILogger" 
          , name =  
          "DatabaseLogger" 
          .  
         
 
          Exception occurred  
          while 
          :  
          while 
          resolving.  
         
 
          Exception is: InvalidOperationException - The type String cannot be constructed. You must configure the container to supply  
          this 
          value. 
         
 
   

如果您想让它使用无参的构造函数创建, 则要使用[InjectionConstructor]特性进行修饰无参的构造函数,

 
          [InjectionConstructor]  
         
          public DatabaseLogger()  
         
          {   
         
          }

若您想使用带参数的构造函数创建对象, 除了在构造函数上使用[InjectionConstructor]外, 还要在创建时传递参数,代码如下

 
          using (IUnityContainer container =  
          new 
          UnityContainer())  
         
          {  
         
          UnityConfigurationSection section = (UnityConfigurationSection)ConfigurationManager.GetSection( 
          "unity" 
          );  
         
          section.Configure(container);  
         
          ILogger logger = container.Resolve<ILogger>( 
          "DatabaseLogger" 
          ,  
         
          new 
          ParameterOverrides{  
         
          { 
          "name" 
          ,  
          "logName" 
          }  
         
          });  
         
          return 
          logger;