asp.net-mvc-2 - MVC 源代码单例模式

Question

为什么.net MVC源代码ControllerBuilder使用委托(delegate)来分配 Controller 工厂？:

private Func<IControllerFactory> _factoryThunk;

public void SetControllerFactory(IControllerFactory controllerFactory) {
    _factoryThunk = () => controllerFactory;
}

为什么不能直接分配ControllerFactory？，即:

private IControllerFactory _factory;

public void SetControllerFactory(IControllerFactory controllerFactory) {
    _factory = controllerFactory;
}

public void SetControllerFactory(Type controllerFactoryType) {
    _factory = (IControllerFactory)Activator.CreateInstance(controllerFactoryType);
}

Answer 1

原因_factoryThunk当前定义为 Func<IControllerFactory>是它是支持两种重载的通用方法:

void SetControllerFactory(Type);
void SetControllerFactory(IControllerFactory);

第一个的实现使用了 _factoryThunk是 Func通过声明 Func使用 Activator 内联实例化 Type懒洋洋:

this._factoryThunk = delegate {
    IControllerFactory factory;
    try
    {
        factory = (IControllerFactory) Activator.CreateInstance(controllerFactoryType);
    }
    catch (Exception exception)
    {
        throw new InvalidOperationException(string.Format(CultureInfo.CurrentUICulture, MvcResources.ControllerBuilder_ErrorCreatingControllerFactory, new object[] { controllerFactoryType }), exception);
    }
    return factory;
};

因此，其他重载看起来具有虚假实现的原因是因为 _factoryThunk被声明为 Func ，您建议的行甚至不会编译:

_factoryThunk = controllerFactory;

_factoryThunk是 Func<IControllerFactory>而controllerFactory是 IControllerFactory -- 不兼容的类型。