延迟/延迟解析

Question

给定以下代码：

public interface IMyContext
{
    string subtype { get; set; }
}

public class MyContext : IMyContext
{
    public string subtype { get; set; }
}

public interface IMyExporter
{
    string Export();
}

public class MyExporterXML : IMyExporter
{
    public string Export()
    {
        return "";
    }
}

public class MyExporterJson : IMyExporter
{
    public string Export()
    {
        return "";
    }
}

public class MyExporterFactory
{
    private IMyContext context;
    public MyExporterFactory(IMyContext context)
    {
        this.context = context;
    }

    public IMyExporter Create()
    {
        switch (context.subtype)
        {
            case "JSON" :
                    return new MyExporterJson();
            default:
                    return new MyExporterXML();
        }
    }
}

public class MyService
{
    private IMyContext context;
    private IMyExporter exporter;
    public MyService(IMyContext context, IMyExporter exporter)
    {
        this.context = context;
        this.exporter = exporter;
    }

    public string Extractdata()
    {
        return exporter.Export();
    }
}

[TestClass]
public class UnitTest2
{
    [TestMethod]
    public void TestMethod1()
    {
        var container = new WindsorContainer();
        container.Register(Component.For<IMyContext>().ImplementedBy<MyContext>());
        container.Register(Component.For<MyExporterFactory>());
        container.Register(Component.For<MyService>());
        container.Register(Component.For<IMyExporter>().UsingFactoryMethod(kernel => kernel.Resolve<MyExporterFactory>().Create()));
        var context = container.Resolve<IMyContext>();
        var service = container.Resolve<MyService>();

        context.subtype = "JSON";

        service.Extractdata();

    }
}

有没有办法在实际使用时解决MyService中的注入导出器?？即。在运行上面的代码时，解析的导出器是MyExporterXML，但由于context.subtype = "JSON“设置，我真的希望它是MyExporterJson。但是，在设置子类型之前解析导出器...

我知道Castle::Windsor有一种叫做基于委托的工厂，但我就是想不出如何使用它……

任何帮助都将不胜感激，TIA

Søren

Answer 1

使用TypeFactoryFacility和自定义ITypedFactoryComponentSelector的组合。这里有一些在你的案例中应该有效的东西。

首先，为工厂创建一个接口：

public interface IMyExporterFactory
{
    IMyExporter GetExporter(IMyContext context);
}

接下来，使用定制的工厂组件选择器，该选择器将使用上下文的子类型来确定组件名称(并更改注册以命名导出器)：

public class ExporterComponentSelector : DefaultTypedFactoryComponentSelector
{
    protected override string GetComponentName(MethodInfo method, object[] arguments)
    {
        if (method.Name == "GetExporter")
        {
            var context = (IMyContext) arguments[0];
            return context.subtype;
        }

        return base.GetComponentName(method, arguments);
    }
}

以下是Windsor注册码的更新，其中包括TypedFactoryFacility和自定义选择器(它根据导出器的子类型命名导出器)：

var container = new WindsorContainer();
container.AddFacility<TypedFactoryFacility>();
container.Register(
    Component.For<IMyExporterFactory>().AsFactory(c => c.SelectedWith(new ExporterComponentSelector())),
    Component.For<IMyExporter>().ImplementedBy<MyExporterJson>().Named("json"),
    Component.For<IMyExporter>().ImplementedBy<MyExporterXML>().Named("xml"),
    Component.For<IMyContext>().ImplementedBy<MyContext>(),
    Component.For<MyService>()
    );

现在，您的服务只是接收一个IMyExporterFactory并使用它来解析导出器：

public class MyService
{
    private readonly IMyContext context;
    private readonly IMyExporterFactory exporterFactory;

    public MyService(IMyContext context, IMyExporterFactory exporterFactory)
    {
        this.context = context;
        this.exporterFactory = exporterFactory;
    }

    public string Extractdata()
    {
        var exporter = exporterFactory.GetExporter(context);
        return exporter.Export();
    }
}

如果组件是用小写名称("xml“、"json")注册的，您可能希望确保代码始终使用小写名称(或者在ExporterComponentSelector中使用context.subtype.ToLower() )。