Unity中使用多构造函数

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:

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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>

如果DatabaseLogger类中的有两个构造函数, 代码如下

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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创建对象, 会抛出以下异常:

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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.

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,

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[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

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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;