dependency-injection - 如何使用 StructureMap 为静态类指定 setter 注入(inject)？

Question

我目前正在研究设计模式书中的这段代码:

public static class DomainEvents
{
    public static IDomainEventHandlerFactory DomainEventHandlerFactory { get; set; }

    public static void Raise<T>(T domainEvent) where T : IDomainEvent
    {
        DomainEventHandlerFactory.GetDomainEventHandlersFor(domainEvent).ForEach(h => h.Handle(domainEvent));
    }
}

这涉及连接 DomainEvents，这个特定的代码片段负责允许我通过 DomainEvents 上的 Raise 方法引发事件。

这是我的 Bootstrapper 文件中的代码:

public class ControllerRegistry : Registry
{
        public ControllerRegistry()
        {
            ForRequestedType<IDomainEventHandlerFactory>().TheDefault.Is.OfConcreteType<StructureMapDomainEventHandlerFactory>();
            ForRequestedType<IDomainEventHandler<OrderSubmittedEvent>>().AddConcreteType<OrderSubmittedHandler>();
        }
    }

当我从服务层访问 DomainEvents.Raise 时(在本例中，我正在引发 OrderSumittedEvent)，DomainEvents是 null(当它应该通过 StructureMap 设置时):

public class OrderService
{
    public void Create(Order order)
    {
        DomainEvents.Raise(new OrderSubmittedEvent() { Order = order });
    }
}

除非我手动将 DomainEvents.DomainEventHandlerFactory 显式设置为 StructureMapDomainEventHandlerFactory，如下所示:

public class OrderService
{
    public void Create(Order order)
    {
        // this is the manual assignment I have to make into the DomainEventHandlerFactory of
        // the static DomainEvents class. Basically, this is what StructureMap should take care
        // of for me, but is not.
        DomainEvents.DomainEventHandlerFactory = new StructureMapDomainEventHandlerFactory();

        DomainEvents.Raise(new OrderSubmittedEvent() { Order = order });
    }
}

下面是使用 .WhatDoIHave() 的 StrucutureMap 的输出，看起来 StructureMap 确实有 StructureMapDomainEventHandlerFactory 类型的配置实例 IDomainEventHandlerFactory。这是转储:

================================================================================================================================================================================================================================================================================================================================================================================================
PluginType                                                                                  Name                                                                                                                          Description                                                                                                                                                           
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Func`1<TResult> (Func`1<TResult>)                                                                                                                                                                                                                                                                                                                                                               
Scoped as:  Transient

                                                                                        311731d7-60c7-46de-9ef4-24608f21df04                                                                                                                                                                                                                                                                
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
IDomainEventHandlerFactory (DE.Infrastructure.Domain.Events.IDomainEventHandlerFactory)     dbcb010c-fa92-4137-85b8-161ab17c2c98                                                                                          Configured Instance of DE.Infrastructure.Domain.Events.StructureMapDomainEventHandlerFactory, DE.Infrastructure, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
Scoped as:  Transient

                                                                                            dbcb010c-fa92-4137-85b8-161ab17c2c98                                                                                          Configured Instance of DE.Infrastructure.Domain.Events.StructureMapDomainEventHandlerFactory, DE.Infrastructure, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
IDomainEventHandler`1<OrderSubmittedEvent> (IDomainEventHandler`1<OrderSubmittedEvent>)     DE.Services.DomainEventHandlers.OrderSubmittedHandler, DE.Services, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null     Configured Instance of DE.Services.DomainEventHandlers.OrderSubmittedHandler, DE.Services, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null                      
Scoped as:  Transient

                                                                                            DE.Services.DomainEventHandlers.OrderSubmittedHandler, DE.Services, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null     Configured Instance of DE.Services.DomainEventHandlers.OrderSubmittedHandler, DE.Services, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null                      
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
IContainer (StructureMap.IContainer)                                                        e24f9e45-caaf-48b6-89f7-d8125310102a                                                                                          Object:  StructureMap.Container                                                                                                                                       
Scoped as:  Transient

                                                                                            e24f9e45-caaf-48b6-89f7-d8125310102a                                                                                          Object:  StructureMap.Container                                                                                                                                       
================================================================================================================================================================================================================================================================================================================================================================================================

我使用过 StructureMap，但我没有使用 Setter 注入(inject)，我也不必处理将 StructureMap 与静态类一起使用(如果这有意义的话)，所以我有点迷茫为什么要使用这段代码行不通。

是否可以将 Setter 注入(inject)与这样的类的静态实现一起使用？我没有正确使用 StructureMap 吗？StructureMap 是否应该负责将 DomainEvents 类创建为单例，并且我可以摆脱静态实现？

谢谢，迈克

Answer 1

Is it possible to use Setter Injection with a static implementation of a class like this?

没有。只有可创建的类才有可能。

Am I not using StructureMap properly?

你不是。依赖注入(inject)处理创建和提供实例。根据定义，静态类在代码中不可创建，因此不可注入(inject)。

Should StructureMap be responsible for creating the DomainEvents class as a Singleton, and I can get rid of the static implementation?

看起来这种设计的核心特征是使用单个实例，因此事件只触发一次。我不确定你想要什么设计模式，但在很多情况下你可以用 Action<T> 代替或 Func<T>对于事件，如果您正确使用单例生活方式，您可能可以注册一个可以在所有类之间共享的实例，而不是求助于静态类。

如果绝对需要静态事件，您可以在您的应用程序启动代码中注入(inject)一个 IDomainEventHandlerFactory 实例，方法是在您完成注册代码(在您的 composition root 中)后手动解析并设置它。

// Provide the DI container with configuration
var container = DIConfig();

// Set the static event
DomainEvents.DomainEventHandlerFactory = container.Resolve<IDomainEventHandlerFactory>();

为确保您的应用程序不会通过多次调用或在设置之前使用它来滥用 setter ，您可以在静态类中放置一些保护子句。

public static class DomainEvents
{
    private static IDomainEventHandlerFactory domainEventHandlerFactory;

    public static IDomainEventHandlerFactory DomainEventHandlerFactory 
    { 
        get
        {
            return domainEventHandlerFactory;
        }
        set
        {
            if (value == null)
                throw new ArgumentNullException("value");
            if (domainEventHandlerFactory != null)
                throw new ArgumentException("DomainEventHandlerFactory is already set and cannot be set again.");
            domainEventHandlerFactory = value;
        }
    }

    public static void Raise<T>(T domainEvent) where T : IDomainEvent
    {
        ThrowIfNotInitialized()
        DomainEventHandlerFactory.GetDomainEventHandlersFor(domainEvent).ForEach(h => h.Handle(domainEvent));
    }

    private static void ThrowIfNotInitialized()
    {
        if (domainEventHandlerFactory == null)
        {
            throw new MvcSiteMapException("Not initialized. You must set DomainEventHandlerFactory at application start.");
        }
    }
}