之前實現的那版依賴註入框架基本可用，但是感覺還是不夠靈活，而且註冊服務和解析服務在同一個地方感覺有點彆扭，有點職責分離不夠。於是借鑒 Autofac 的做法，增加了一個 `ServiceContainerBuilder` 來負責註冊服務，`ServiceContainer`負責解析服務，並且增加了一... ...

動手造輪子：實現一個簡單的依賴註入(二) --- 服務註冊優化

Intro

之前實現的那版依賴註入框架基本可用，但是感覺還是不夠靈活，而且註冊服務和解析服務在同一個地方感覺有點彆扭，有點職責分離不夠。於是借鑒 Autofac 的做法，增加了一個 ServiceContainerBuilder 來負責註冊服務，ServiceContainer負責解析服務，並且增加了一個 ServiceContainerModule 可以支持像 Autofac 中 Module/RegisterAssemblyModules 一樣註冊服務

實現代碼

ServiceContainerBuilder

增加 ServiceContainerBuild 來專門負責註冊服務，原來註冊服務的那些擴展方法則從 IServiceContainer 的擴展方法變成 IServiceContainerBuilder 的擴展

public interface IServiceContainerBuilder
{
    IServiceContainerBuilder Add(ServiceDefinition item);

    IServiceContainerBuilder TryAdd(ServiceDefinition item);

    IServiceContainer Build();
}

public class ServiceContainerBuilder : IServiceContainerBuilder
{
    private readonly List<ServiceDefinition> _services = new List<ServiceDefinition>();

    public IServiceContainerBuilder Add(ServiceDefinition item)
    {
        if (_services.Any(_ => _.ServiceType == item.ServiceType && _.GetImplementType() == item.GetImplementType()))
        {
            return this;
        }

        _services.Add(item);
        return this;
    }

    public IServiceContainerBuilder TryAdd(ServiceDefinition item)
    {
        if (_services.Any(_ => _.ServiceType == item.ServiceType))
        {
            return this;
        }
        _services.Add(item);
        return this;
    }

    public IServiceContainer Build() => new ServiceContainer(_services);
}

IServiceContainer

增加 ServiceContainerBuilder 之後就不再支持註冊服務了，ServiceContainer 這個類型也可以變成一個內部類了，不必再對外暴露

public interface IServiceContainer : IScope, IServiceProvider
{
    IServiceContainer CreateScope();
}

internal class ServiceContainer : IServiceContainer
{
    private readonly IReadOnlyList<ServiceDefinition> _services;
    
    public ServiceContainer(IReadOnlyList<ServiceDefinition> serviceDefinitions)
    {
        _services = serviceDefinitions;
        // ...
    }
    
    // 此處約省略一萬行代碼 ...
}

ServiceContainerModule

定義了一個 ServiceContainerModule 來實現像 Autofac 那樣，在某一個程式集內定義一個 Module 註冊程式集內需要註冊的服務，在服務註冊的地方調用 RegisterAssemblyModules 來掃描所有程式集並註冊自定義 ServiceContainerModule 需要註冊的服務

public interface IServiceContainerModule
{
    void ConfigureServices(IServiceContainerBuilder serviceContainerBuilder);
}

public abstract class ServiceContainerModule : IServiceContainerModule
{
    public abstract void ConfigureServices(IServiceContainerBuilder serviceContainerBuilder);
}

自定義 ServiceContainerModule 使用示例：

public class TestServiceContainerModule : ServiceContainerModule
{
    public override void ConfigureServices(IServiceContainerBuilder serviceContainerBuilder)
    {
        serviceContainerBuilder.AddSingleton<IIdGenerator>(GuidIdGenerator.Instance);
    }
}

RegisterAssemblyModules 擴展方法實現如下：


public static IServiceContainerBuilder RegisterAssemblyModules(
    [NotNull] this IServiceContainerBuilder serviceContainerBuilder, params Assembly[] assemblies)
{
    #if NET45
        // 解決 asp.net 在 IIS 下應用程式域被回收的問題
        // https://autofac.readthedocs.io/en/latest/register/scanning.html#iis-hosted-web-applications
        if (null == assemblies || assemblies.Length == 0)
        {
            if (System.Web.Hosting.HostingEnvironment.IsHosted)
            {
                assemblies = System.Web.Compilation.BuildManager.GetReferencedAssemblies()
                    .Cast<Assembly>().ToArray();
            }
        }
    #endif

        if (null == assemblies || assemblies.Length == 0)
        {
            assemblies = AppDomain.CurrentDomain.GetAssemblies();
        }

    foreach (var type in assemblies.WhereNotNull().SelectMany(ass => ass.GetTypes())
             .Where(t => t.IsClass && !t.IsAbstract && typeof(IServiceContainerModule).IsAssignableFrom(t))
            )
    {
        try
        {
            if (Activator.CreateInstance(type) is ServiceContainerModule module)
            {
                module.ConfigureServices(serviceContainerBuilder);
            }
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
        }
    }
    return serviceContainerBuilder;
}

使用示例

使用起來除了註冊服務變化了之外，別的地方並沒有什麼不同，看一下單元測試代碼

public class DependencyInjectionTest : IDisposable
{
    private readonly IServiceContainer _container;

    public DependencyInjectionTest()
    {
        var containerBuilder = new ServiceContainerBuilder();
        containerBuilder.AddSingleton<IConfiguration>(new ConfigurationBuilder().Build());
        containerBuilder.AddScoped<IFly, MonkeyKing>();
        containerBuilder.AddScoped<IFly, Superman>();

        containerBuilder.AddScoped<HasDependencyTest>();
        containerBuilder.AddScoped<HasDependencyTest1>();
        containerBuilder.AddScoped<HasDependencyTest2>();
        containerBuilder.AddScoped<HasDependencyTest3>();
        containerBuilder.AddScoped(typeof(HasDependencyTest4<>));

        containerBuilder.AddTransient<WuKong>();
        containerBuilder.AddScoped<WuJing>(serviceProvider => new WuJing());
        containerBuilder.AddSingleton(typeof(GenericServiceTest<>));
        
        containerBuilder.RegisterAssemblyModules();

        _container = containerBuilder.Build();
    }

    [Fact]
    public void Test()
    {
        var rootConfig = _container.ResolveService<IConfiguration>();

        Assert.Throws<InvalidOperationException>(() => _container.ResolveService<IFly>());
        Assert.Throws<InvalidOperationException>(() => _container.ResolveRequiredService<IDependencyResolver>());

        using (var scope = _container.CreateScope())
        {
            var config = scope.ResolveService<IConfiguration>();

            Assert.Equal(rootConfig, config);

            var fly1 = scope.ResolveRequiredService<IFly>();
            var fly2 = scope.ResolveRequiredService<IFly>();
            Assert.Equal(fly1, fly2);

            var wukong1 = scope.ResolveRequiredService<WuKong>();
            var wukong2 = scope.ResolveRequiredService<WuKong>();

            Assert.NotEqual(wukong1, wukong2);

            var wuJing1 = scope.ResolveRequiredService<WuJing>();
            var wuJing2 = scope.ResolveRequiredService<WuJing>();

            Assert.Equal(wuJing1, wuJing2);

            var s0 = scope.ResolveRequiredService<HasDependencyTest>();
            s0.Test();
            Assert.Equal(s0._fly, fly1);

            var s1 = scope.ResolveRequiredService<HasDependencyTest1>();
            s1.Test();

            var s2 = scope.ResolveRequiredService<HasDependencyTest2>();
            s2.Test();

            var s3 = scope.ResolveRequiredService<HasDependencyTest3>();
            s3.Test();

            var s4 = scope.ResolveRequiredService<HasDependencyTest4<string>>();
            s4.Test();

            using (var innerScope = scope.CreateScope())
            {
                var config2 = innerScope.ResolveRequiredService<IConfiguration>();
                Assert.True(rootConfig == config2);

                var fly3 = innerScope.ResolveRequiredService<IFly>();
                fly3.Fly();

                Assert.NotEqual(fly1, fly3);
            }

            var flySvcs = scope.ResolveServices<IFly>();
            foreach (var f in flySvcs)
                f.Fly();
        }

        var genericService1 = _container.ResolveRequiredService<GenericServiceTest<int>>();
        genericService1.Test();

        var genericService2 = _container.ResolveRequiredService<GenericServiceTest<string>>();
        genericService2.Test();
    }

    public void Dispose()
    {
        _container.Dispose();
    }
}