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:

    using (IUnityContainer container = new UnityContainer())
    {
    	UnityConfigurationSection section = (UnityConfigurationSection)ConfigurationManager.GetSection("unity");
    	section.Configure(container);    //...
    	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;
	}