Unity中使用多构造函数

若是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以下:

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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

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<?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>

若是DatabaseLogger类中的有两个构造函数, 代码以下

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

则Unity自动使用参数最多的构造函数进行建立对象, 会抛出如下异常:

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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.

若是您想让它使用无参的构造函数建立, 则要使用[InjectionConstructor]特性进行修饰无参的构造函数,

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[InjectionConstructor] public DatabaseLogger() {  }

若您想使用带参数的构造函数建立对象, 除了在构造函数上使用[InjectionConstructor]外, 还要在建立时传递参数,代码以下

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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;