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 occurredwhile:while resolving.
Exception is: InvalidOperationException - The type String cannot be constructed. You must configure the container to supplythis 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;