Castle IOC 實踐：FactorySupport Facility

核心價值：整合既有工廠模式

FactorySupport Facility 允許使用現有工廠建立組件實例，將既有物件模型納入容器自動裝配體系。支援兩種策略：

1. 透過存取器訪問實例（如 Singleton 模式的靜態 Instance 屬性）
2. 透過靜態方法或實例方法建立實例

為何需要它？對比傳統用法

傳統寫法：程式碼中直接 new 工廠再取得組件，產生硬性依賴。

public class App {
    static void Main() {
        MyFactory factory = new MyFactory();
        IComponent comp = factory.Create();
        comp.Display();
    }
}

使用 Facility 後：工廠與組件代碼不變，透過配置檔交給容器管理：

<facilities>
  <facility id="factorysupport" type="Castle.Facilities.FactorySupport.FactorySupportFacility, Castle.MicroKernel" />
</facilities>
<components>
  <component id="myfactory" type="FactorySupportDemo.MyFactory, FactorySupportDemo" />
  <component id="mycomp" type="FactorySupportDemo.MyComponent, FactorySupportDemo"
    factoryId="myfactory" factoryCreate="Create"></component>
</components>

public class App {
    static void Main() {
        IWindsorContainer container = new WindsorContainer("../../Basic.xml");
        IComponent instance = (IComponent)container["mycomp"];
        instance.Display(); // 完全無 new 關鍵字
    }
}

使用方式

1. 加入 Facility

// 程式碼方式
container.AddFacility("factorysupport", new FactorySupportFacility());
// 配置檔方式
<facility id="factorysupport" type="Castle.Facilities.FactorySupport.FactorySupportFacility, Castle.MicroKernel" />

2. 組件配置指定建立策略

• 存取器模式：instance-accessor="Instance"
• 工廠方法模式：factoryId="myfactory" factoryCreate="Create"

常見配置範例

範例 1：Singleton 存取器

public class SingletonWithAccessor {
    private static readonly SingletonWithAccessor instance = new SingletonWithAccessor();
    private SingletonWithAccessor() {}
    public static SingletonWithAccessor Instance { get { return instance; } }
}

<component id="accessor.comp" type="...SingletonWithAccessor,..." instance-accessor="Instance"></component>

範例 2：一般工廠

<component id="mycompfactory" type="...MyCompFactory,..." />
<component id="mycomp" type="...MyComp,..." factoryId="mycompfactory" factoryCreate="Create"></component>

範例 3：帶參數工廠

<component id="mycompfactory" type="...MyCompFactory2,..."></component>
<component id="mycomp" type="...MyComp,..." factoryId="mycompfactory" factoryCreate="Create">
  <parameters>
    <storeName>MyStore</storeName>
    <props>
      <dictionary>
        <entry key="key1">item1</entry>
        <entry key="key2">item2</entry>
      </dictionary>
    </props>
  </parameters>
</component>

範例 4：自動裝配工廠參數

<component id="myserv" service="...IMyService,..." type="...DefaultMyService,..." />
<component id="mycompfactory" type="...MyCompFactory3,..."></component>
<component id="mycomp" type="...MyComp,..." factoryId="mycompfactory" factoryCreate="Create"></component>

容器自動解析 IMyService 傳給工廠 Create 方法。

實現原理

根據配置決定使用 AccessorActivator 或 FactoryActivator：

string instanceAccessor = model.Configuration.Attributes["instance-accessor"];
string factoryId = model.Configuration.Attributes["factoryId"];
string factoryCreate = model.Configuration.Attributes["factoryCreate"];
if (instanceAccessor != null) {
    model.ExtendedProperties.Add("instance.accessor", instanceAccessor);
    model.CustomComponentActivator = typeof(AccessorActivator);
} else if (factoryId != null) {
    model.ExtendedProperties.Add("factoryId", factoryId);
    model.ExtendedProperties.Add("factoryCreate", factoryCreate);
    model.CustomComponentActivator = typeof(FactoryActivator);
}

更多 Castle 系列文章請參考《Castle 開發系列文章》。