动手造轮子：实现一个简单的依赖注入(二) --- 服务注册优化

Intro

之前实现的那版依赖注入框架基本可用，但是感觉还是不够灵活，而且注册服务和解析服务在同一个地方感觉有点别扭，有点职责分离不够。于是借鉴 Autofac 的做法，增加了一个 ServiceContainerBuilder 来负责注册服务， ServiceContainer负责解析服务，并且增加了一个 ServiceContainerModule 可以支持像 Autofac 中 Module/ RegisterAssemblyModules 一样注册服务

实现代码

ServiceContainerBuilder

增加 ServiceContainerBuild 来专门负责注册服务，原来注册服务的那些扩展方法则从 IServiceContainer 的扩展方法变成 IServiceContainerBuilder 的扩展

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 之后就不再支持注册服务了， ServiceContainer 这个类型也可以变成一个内部类了，不必再对外暴露

public interface IServiceContainer : IScope, IServiceProvider
{
 IServiceContainer CreateScope();
}
internal class ServiceContainer : IServiceContainer
{
 private readonly IReadOnlyList<ServiceDefinition> _services;
 public ServiceContainer(IReadOnlyList<ServiceDefinition> serviceDefinitions)
 {
 _services = serviceDefinitions;
 // ...
 }
 // 此处约省略一万行代码 ...
}

ServiceContainerModule

定义了一个 ServiceContainerModule 来实现像 Autofac 那样，在某一个程序集内定义一个 Module 注册程序集内需要注册的服务，在服务注册的地方调用 RegisterAssemblyModules 来扫描所有程序集并注册自定义 ServiceContainerModule 需要注册的服务

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

自定义 ServiceContainerModule 使用示例：

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

RegisterAssemblyModules 扩展方法实现如下：

public static IServiceContainerBuilder RegisterAssemblyModules(
 [NotNull] this IServiceContainerBuilder serviceContainerBuilder, params Assembly[] assemblies)
{
 #if NET45
 // 解决 asp.net 在 IIS 下应用程序域被回收的问题
 // 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

使用起来除了注册服务变化了之外，别的地方并没有什么不同，看一下单元测试代码

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();
 }
}

Reference

• https://github.com/WeihanLi/WeihanLi.Common/tree/dev/src/WeihanLi.Common/DependencyInjection

• https://www.cnblogs.com/weihanli/p/implement-dependency-injection-01.html

• https://www.cnblogs.com/weihanli/p/implement-dependency-injection.html

• https://autofac.org/

• https://autofac.readthedocs.io/en/latest/register/scanning.html