Unity中使用多構造函數

若是要實例化的類只有一個構造函數, 則使用方法很簡單使用方法以下:

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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; }

其中配置文件爲

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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類中的有兩個構造函數, 代碼以下

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

則Unity自動使用參數最多的構造函數進行建立對象, 會拋出如下異常:

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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.

若是您想讓它使用無參的構造函數建立, 則要使用[InjectionConstructor]特性進行修飾無參的構造函數,

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[InjectionConstructor] public DatabaseLogger() {  }

若您想使用帶參數的構造函數建立對象, 除了在構造函數上使用[InjectionConstructor]外, 還要在建立時傳遞參數,代碼以下

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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;