获取所有已实现接口的列表

Question

我有3个具有相同界面的类：

cppTopicGenerator : TopicGenerator
phpTopicGenerator : TopicGenerator
javaTopicGenerator : TopicGenerator

我为他们创建了一个外观，我尝试使用它们，如下所示：

public class MyFacade 
{
    private readonly List<TopicGenerator> generators;

    public void BusinessLogic(string extension)
    {
            MyParser(extenstion).generate();
    }


    private TopicGenerator MyParser(string extension)
    {
        foreach (var generator in generators)
        {
            if (generator.Accept(extension))
            {
                return generator;
            }
        }
        throw new NotFoundException($"Generator for {extension} doesnt exist.");
    }
}

问题是，应该如何创建这个生成器列表？我需要手动创建所有生成器的列表，如：

private readonly List<TopicGenerator> generators = new List(
        {
            new CppTopicGenerator()
            new PhpTopicGenerator()
            new JavaTopicGenerator()
        });

或者是否有可能以某种方式自动注入它们？

Answer 1

肯定是的，你可以通过IoC容器注入它。但是，这取决于您的需求。如果您的Generator太复杂并且需要大量参考，您可以使用IoC（e.x.Autofac），但如果它是轻量级的，我更喜欢手动创建它。

示例（控制台应用程序中的所有示例）：1）手动

using System;
using System.Collections.Generic;

namespace Test
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");

            var service = new MyFacade();

            service.MyParser("foo");
            service.MyParser("bar");
            service.MyParser("foobar");
        }
    }

    public class MyFacade
    {
        private readonly IEnumerable<IGenerator> _generators;

        public MyFacade()
        {
            _generators = new List<IGenerator>()
            {
                new CppTopicGenerator(),
                new PhpTopicGenerator(),
                new JavaTopicGenerator(),
            };
        }

        public IGenerator MyParser(string extension)
        {
            foreach (var generator in _generators)
            {
                if (generator.Accept(extension))
                {
                    return generator;
                }
            }

            throw new NotFoundException($"Generator for {extension} doesnt exist.");
        }
    }

    public interface IGenerator
    {
        bool Accept(string extension);
    }

    public class CppTopicGenerator : IGenerator
    {
        public bool Accept(string extension)
        {
            Console.WriteLine("CppTopicGenerator checking executed");
            return extension == "foo";
        }
    }

    public class PhpTopicGenerator : IGenerator
    {
        public bool Accept(string extension)
        {
            Console.WriteLine("PhpTopicGenerator checking executed");
            return extension == "bar";
        }
    }

    public class JavaTopicGenerator : IGenerator
    {
        public bool Accept(string extension)
        {
            Console.WriteLine("JavaTopicGenerator checking executed");
            return extension == "foobar";
        }
    }
}

2）Autofac：

class MainClass
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");

            var builder = new ContainerBuilder();

            builder.RegisterAssemblyTypes(AppDomain.CurrentDomain.GetAssemblies()).As<IGenerator>();
            builder.RegisterType<MyFacade>();

            var container = builder.Build();

            using (var scope = container.BeginLifetimeScope())
            {
                var service = scope.Resolve<MyFacade>();

                service.MyParser("foo");
                service.MyParser("bar");
                service.MyParser("foobar");
            }
        }
    }

    public class MyFacade
    {
        private readonly IEnumerable<IGenerator> _generators;

        public MyFacade(IEnumerable<IGenerator> generators)
        {
            _generators = generators;
        }

        public IGenerator MyParser(string extension)
        {
            foreach (var generator in _generators)
            {
                if (generator.Accept(extension))
                {
                    return generator;
                }
            }

            throw new NotFoundException($"Generator for {extension} doesnt exist.");
        }
    }

    public interface IGenerator
    {
        bool Accept(string extension);
    }

    public class CppTopicGenerator : IGenerator
    {
        public bool Accept(string extension)
        {
            Console.WriteLine("CppTopicGenerator checking executed");
            return extension == "foo";
        }
    }

    public class PhpTopicGenerator : IGenerator
    {
        public bool Accept(string extension)
        {
            Console.WriteLine("PhpTopicGenerator checking executed");
            return extension == "bar";
        }
    }

    public class JavaTopicGenerator : IGenerator
    {
        public bool Accept(string extension)
        {
            Console.WriteLine("JavaTopicGenerator checking executed");
            return extension == "foobar";
        }
    }

Answer 2

您可以从Assembly中反映它们，然后通过Activator实例化它们：

    public MyFacade() {
        //Reflect them
        var type = typeof(TopicGenerator);
        var types = AppDomain.CurrentDomain.GetAssemblies()
        .SelectMany(s => s.GetTypes())
        .Where(p => type.IsAssignableFrom(p) && !p.IsInterface);
        //Instantiate them
        generators = types.Select(t => Activator.CreateInstance(t) as TopicGenerator).ToList();
    }

通过这种方式，您可以找到实现TopicGenerator的所有类，如果您创建一个新类，则无需手动添加它们。

Answer 3

您可以使用以下方法生成列表。

var list = AppDomain.CurrentDomain.GetAssemblies()
                    .SelectMany(x => x.GetTypes())
                    .Where(p => typeof(TopicGenerator).IsAssignableFrom(p) && p.IsClass && !p.IsAbstract)
                    .Select(x => (TopicGenerator)Activator.CreateInstance(x)).ToList<TopicGenerator>();

它的作用是，它反映并迭代汇编中的类型并检查是否实现了特定的接口。 !p.IsAbstract将确保未列出抽象类。

Answer 4

您可以使用reflection来实现此目的。

private static readonly List<TopicGenerator> generators = 
    Assembly.GetExecutingAssembly().GetTypes()
        .Where(x => x.ImplementedInterfaces.Contains(typeof(TopicGenerator)))
        .Select(x => (TopicGenerator)Activator.CreateInstance(x))
        .ToList();