c# - Unity 的自定义对象工厂扩展

Question

我正在使用 Unity IoC 容器，我需要拦截对特定基础接口(interface)的任何 Resolve 调用，并运行我自己的自定义代码来构造这些类型。

换句话说，在下面的示例代码中，当我调用 container.Resolve<IFooN>() 时, 如果它没有具体实现类型的实例，它会调用 MyFactoryFunction构造一个，否则我希望它返回缓存的副本。

标准的 Unity 容器无法构造这些对象(更新: 因为它们是 .NET 远程对象，所以具体类不存在于本地计算机上的任何程序集中)，我不想预先创建它们并使用 RegisterInstance 存储它们。

interface IFoo : IBase { ... }
interface IFoo2 : IBase { ... }

...
container.Resolve<IFoo2>();

...
IBase MyFactoryFunction(Type t)
{
    ...
}

我假设我可以创建一个 Unity 扩展来执行此操作，但我想知道是否已经有我可以借用的解决方案。

Answer 1

为了完整起见，我应该添加另一个在 Unity 2 下有效的答案，因为我的另一个答案不再有效。它稍微复杂一些，因为您需要制定自定义构建器策略。感谢来自 Unity 项目的 ctavares 在 this thread 上提供了很多帮助在实现中:

public class FactoryUnityExtension : UnityContainerExtension
{
    private ICustomFactory factory;
    private CustomFactoryBuildStrategy strategy;

    public FactoryUnityExtension(ICustomFactory factory)
    {
        this.factory = factory;
    }

    protected override void Initialize()
    {
        this.strategy = new CustomFactoryBuildStrategy(factory, Context);
        Context.Strategies.Add(strategy, UnityBuildStage.PreCreation);
        Context.Policies.Set<ParentMarkerPolicy>(new ParentMarkerPolicy(Context.Lifetime), new NamedTypeBuildKey<ParentMarkerPolicy>());
    }
}

public class ParentMarkerPolicy : IBuilderPolicy
{
    private ILifetimeContainer lifetime;

    public ParentMarkerPolicy(ILifetimeContainer lifetime)
    {
        this.lifetime = lifetime;
    }

    public void AddToLifetime(object o)
    {
        lifetime.Add(o);
    }
}

public interface ICustomFactory
{
    object Create(Type t);
    bool CanCreate(Type t);
}

public class CustomFactoryBuildStrategy : BuilderStrategy
{
    private ExtensionContext baseContext;
    private ICustomFactory factory;


    public CustomFactoryBuildStrategy(ICustomFactory factory, ExtensionContext baseContext)
    {
        this.factory = factory;
        this.baseContext = baseContext;
    }

    public override void PreBuildUp(IBuilderContext context)
    {
        var key = (NamedTypeBuildKey)context.OriginalBuildKey;

        if (factory.CanCreate(key.Type) && context.Existing == null)
        {
            context.Existing = factory.Create(key.Type);
            var ltm = new ContainerControlledLifetimeManager();
            ltm.SetValue(context.Existing);

            // Find the container to add this to
            IPolicyList parentPolicies;
            var parentMarker = context.Policies.Get<ParentMarkerPolicy>(new NamedTypeBuildKey<ParentMarkerPolicy>(), out parentPolicies);

            // TODO: add error check - if policy is missing, extension is misconfigured

            // Add lifetime manager to container
            parentPolicies.Set<ILifetimePolicy>(ltm, new NamedTypeBuildKey(key.Type));
            // And add to LifetimeContainer so it gets disposed
            parentMarker.AddToLifetime(ltm);

            // Short circuit the rest of the chain, object's already created
            context.BuildComplete = true;
        }
    }
}