net core系列：一个接口多个实现类，利用mixin实现属性注入

日行四善 11-26 50

前言：

眼前看官们对“net 开发接口”都比较讲究，兄弟们都想要分析一些“net 开发接口”的相关资讯。那么小编在网摘上搜集了一些对于“net 开发接口””的相关资讯，希望兄弟们能喜欢，兄弟们快快来了解一下吧！

哈哈哈哈，大家好，我就是高产似母猪的三合。日常开发中，我们常会遇到这样的场景，一个接口，有多个实现类，在某个业务中，我们希望指定某个实现类，如今网络上常见的解决方案，就是注入一个委托或者利用工厂模式，这些方式虽然能实现功能，但使用起来还是不够优雅，如何才称得上优雅呢？自然是在添加服务的时候给服务指定名称，注入的时候根据名称来进行注入，没错，就是类似spring boot里的@Qualifier注解，那么net core能实现这个注解么？要知道net core里的原生DI并不支持在注册的时候给服务添加名称，所以实现起来也是难上加难，但是，利用动态代理，我们就能完美解决这个问题，没错，他Lei了，net core版[QualifierAttribute],实现这个注解用到的最核心的技术，就是动态代理中非常重要的mixin，什么是mixin呢？玩过less的小伙伴可能会知道，这玩意可以把2个css样式混合成一个，而在net core中，DP(castle.dynamicproxy)提供的mixin技术，可以在程序运行时，把多个类混合成一个动态代理类，这个混合类既可以用作类1，又可以用作类2，那么思路就很清晰了，类1就是我们注入的服务类，类2需要我们自定义，在我们的这个自定义类中，我们可以添加一个Name的属性，这样在注册服务的时候给服务命名，到了注入的时候，我们就可以根据名称来进行精准地的属性注入。BTW,动态代理，注解式编程，AOP贯穿本系列始终，no bb，正文开始。

1.定义用到的类

定义QualifierAttribute注解

 public class QualifierAttribute : Attribute    {        public string Name { get; }        public QualifierAttribute(string name)        {            if (string.IsNullOrWhiteSpace(name))            {                throw new ArgumentException("服务名称不能为空");            }            this.Name = name;        }    }

定义用来进行混合的附加类接口IDependencyAddition和他的实现类DependencyAddition，类里面只有一个名称的属性。

public interface IDependencyAddition    {        string Name { set; get; }    }

 public class DependencyAddition : IDependencyAddition    {        public string Name { set; get; }    }

第一篇文章里，讲过有一辆汽车，汽车里有引擎，我们在这基础上进行扩展，汽车总是有轮胎的，我们定义一个轮胎接口IWheel和他的2个实现类WheelA和WheelB，类里只有一个Scroll方法，表示轮胎在滚，同时向控制台输出他们是哪种轮胎。

 public interface IWheel    {        void Scroll();    }

  public class WheelA : IWheel    {        public void Scroll()        {            Console.WriteLine("我是A轮胎，我正在滚");        }    }

 public class WheelB : IWheel    {        public void Scroll()        {            Console.WriteLine("我是B轮胎，我正在滚");        }    }

修改汽车类接口ICar和他的实现类Car，主要就是添加了轮胎的属性注入，并且用[Qualifier("B轮胎")]注解指定使用哪种轮胎，然后调用Scroll方法，让轮胎滚起来。

   public interface ICar    {        Engine Engine { set; get; }        IWheel Wheel { set; get; }        void Fire();    }

   public class Car : ICar    {        [Autowired]        public Engine Engine { set; get; }        [Value("oilNo")]        public int OilNo { set; get; }        [Autowired]        [Qualifier("B轮胎")]        public IWheel Wheel { set; get; }        [Transactional]        public void Fire()        {            Console.WriteLine("加满" + OilNo + "号汽油,点火");            Wheel.Scroll();            Engine.Start();        }    }

IServiceCollection的静态扩展类SummerBootExtentions，和上一篇相比，主要是添加了AddSbService的新重载，使注册服务的时候能够为服务添加名称，在这基础上进一步封装了AddSbSingleton，AddSbScoped和AddSbTransient方法。还有在工厂委托函数里进行属性注入的时候，添加了支持[QualifierAttribute]注解的逻辑，完整类代码如下：

public static class SummerBootExtentions    {        /// <summary>        /// 瞬时        /// </summary>        /// <typeparam name="TService"></typeparam>        /// <typeparam name="TImplementation"></typeparam>        /// <param name="services"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbTransient<TService, TImplementation>(this IServiceCollection services, params Type[] interceptorTypes)        {            return services.AddSbService(typeof(TService), typeof(TImplementation), ServiceLifetime.Transient, interceptorTypes);        }        /// <summary>        /// 瞬时        /// </summary>        /// <param name="services"></param>        /// <param name="serviceType"></param>        /// <param name="implementationType"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbTransient(this IServiceCollection services, Type serviceType,            Type implementationType, params Type[] interceptorTypes)        {            return services.AddSbService(serviceType, implementationType, ServiceLifetime.Transient, interceptorTypes);        }        /// <summary>        /// 请求级别        /// </summary>        /// <typeparam name="TService"></typeparam>        /// <typeparam name="TImplementation"></typeparam>        /// <param name="services"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbScoped<TService, TImplementation>(this IServiceCollection services, params Type[] interceptorTypes)        {            return services.AddSbService(typeof(TService), typeof(TImplementation), ServiceLifetime.Scoped, interceptorTypes);        }        /// <summary>        /// 请求级别        /// </summary>        /// <param name="services"></param>        /// <param name="serviceType"></param>        /// <param name="implementationType"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbScoped(this IServiceCollection services, Type serviceType,            Type implementationType, params Type[] interceptorTypes)        {            return services.AddSbService(serviceType, implementationType, ServiceLifetime.Scoped, interceptorTypes);        }        /// <summary>        /// 单例        /// </summary>        /// <typeparam name="TService"></typeparam>        /// <typeparam name="TImplementation"></typeparam>        /// <param name="services"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbSingleton<TService, TImplementation>(this IServiceCollection services, params Type[] interceptorTypes)        {            return services.AddSbService(typeof(TService), typeof(TImplementation), ServiceLifetime.Singleton, interceptorTypes);        }        /// <summary>        /// 单例        /// </summary>        /// <param name="services"></param>        /// <param name="serviceType"></param>        /// <param name="implementationType"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbSingleton(this IServiceCollection services, Type serviceType,            Type implementationType, params Type[] interceptorTypes)        {            return services.AddSbService(serviceType, implementationType, ServiceLifetime.Singleton, interceptorTypes);        }        public static IServiceCollection AddSbService(this IServiceCollection services, Type serviceType, Type implementationType,            ServiceLifetime lifetime, params Type[] interceptorTypes)        {            services.Add(new ServiceDescriptor(implementationType, implementationType, lifetime));            object Factory(IServiceProvider provider)            {                var target = provider.GetService(implementationType);                var properties = implementationType.GetTypeInfo().DeclaredProperties;                foreach (PropertyInfo info in properties)                {                    //属性注入                    if (info.GetCustomAttribute<AutowiredAttribute>() != null)                    {                        var propertyType = info.PropertyType;                        object impl = null;                        var qualifierAttribute = info.GetCustomAttribute<QualifierAttribute>();                        if (qualifierAttribute != null)                        {                            var serviceName = qualifierAttribute.Name;                            var implList = provider.GetServices(propertyType);                            foreach (var tmpImpl in implList)                            {                                if (ProxyUtil.IsProxy(tmpImpl))                                {                                    var addition = tmpImpl as IDependencyAddition;                                    if (addition?.Name == serviceName)                                    {                                        impl = tmpImpl;                                        break; ;                                    }                                }                            }                        }                        else                        {                            impl = provider.GetService(propertyType);                        }                        if (impl != null)                        {                            info.SetValue(target, impl);                        }                    }                    //配置值注入                    if (info.GetCustomAttribute<ValueAttribute>() is ValueAttribute valueAttribute)                    {                        var value = valueAttribute.Value;                        if (provider.GetService(typeof(IConfiguration)) is IConfiguration configService)                        {                            var pathValue = configService.GetSection(value).Value;                            if (pathValue != null)                            {                                var pathV = Convert.ChangeType(pathValue, info.PropertyType);                                info.SetValue(target, pathV);                            }                        }                    }                }                List<IInterceptor> interceptors = interceptorTypes.ToList()                    .ConvertAll<IInterceptor>(interceptorType => provider.GetService(interceptorType) as IInterceptor);                var proxyGenerator = provider.GetService<ProxyGenerator>();                var proxy = proxyGenerator.CreateInterfaceProxyWithTarget(serviceType, target, interceptors.ToArray());                return proxy;            };            var serviceDescriptor = new ServiceDescriptor(serviceType, Factory, lifetime);            services.Add(serviceDescriptor);            return services;        }        /// <summary>        /// 瞬时        /// </summary>        /// <typeparam name="TService"></typeparam>        /// <param name="services"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbTransient<TService>(this IServiceCollection services, params Type[] interceptorTypes)        {            return services.AddSbService(typeof(TService), ServiceLifetime.Transient, interceptorTypes);        }        /// <summary>        /// 瞬时        /// </summary>        /// <param name="services"></param>        /// <param name="serviceType"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbTransient(this IServiceCollection services, Type serviceType, params Type[] interceptorTypes)        {            return services.AddSbService(serviceType, ServiceLifetime.Transient, interceptorTypes);        }        /// <summary>        /// 请求        /// </summary>        /// <typeparam name="TService"></typeparam>        /// <param name="services"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbScoped<TService>(this IServiceCollection services, params Type[] interceptorTypes)        {            return services.AddSbService(typeof(TService), ServiceLifetime.Scoped, interceptorTypes);        }        /// <summary>        /// 请求        /// </summary>        /// <param name="services"></param>        /// <param name="serviceType"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbScoped(this IServiceCollection services, Type serviceType,             params Type[] interceptorTypes)        {            return services.AddSbService(serviceType, ServiceLifetime.Scoped, interceptorTypes);        }        /// <summary>        /// 单例        /// </summary>        /// <typeparam name="TService"></typeparam>        /// <param name="services"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbSingleton<TService>(this IServiceCollection services, params Type[] interceptorTypes)        {            return services.AddSbService(typeof(TService), ServiceLifetime.Singleton, interceptorTypes);        }        /// <summary>        /// 单例        /// </summary>        /// <param name="services"></param>        /// <param name="serviceType"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbSingleton(this IServiceCollection services, Type serviceType, params Type[] interceptorTypes)        {            return services.AddSbService(serviceType, ServiceLifetime.Singleton, interceptorTypes);        }        public static IServiceCollection AddSbService(this IServiceCollection services, Type serviceType,            ServiceLifetime lifetime, params Type[] interceptorTypes)        {            if (services == null)                throw new ArgumentNullException(nameof(services));            if (serviceType == (Type)null)                throw new ArgumentNullException(nameof(serviceType));            object Factory(IServiceProvider provider)            {                List<IInterceptor> interceptors = interceptorTypes.ToList()                    .ConvertAll<IInterceptor>(interceptorType => provider.GetService(interceptorType) as IInterceptor);                var proxyGenerator = provider.GetService<ProxyGenerator>();                var proxy = proxyGenerator.CreateClassProxy(serviceType, interceptors.ToArray());                var properties = serviceType.GetTypeInfo().DeclaredProperties;                foreach (PropertyInfo info in properties)                {                    //属性注入                    if (info.GetCustomAttribute<AutowiredAttribute>() != null)                    {                        var propertyType = info.PropertyType;                        object impl = null;                        var qualifierAttribute = info.GetCustomAttribute<QualifierAttribute>();                        if (qualifierAttribute != null)                        {                            var serviceName = qualifierAttribute.Name;                            var implList = provider.GetServices(propertyType);                            foreach (var tmpImpl in implList)                            {                                if (ProxyUtil.IsProxy(tmpImpl))                                {                                    var addition = tmpImpl as IDependencyAddition;                                    if (addition?.Name == serviceName)                                    {                                        impl = tmpImpl;                                        break; ;                                    }                                }                            }                        }                        else                        {                            impl = provider.GetService(propertyType);                        }                        if (impl != null)                        {                            info.SetValue(proxy, impl);                        }                    }                    //配置值注入                    if (info.GetCustomAttribute<ValueAttribute>() is ValueAttribute valueAttribute)                    {                        var value = valueAttribute.Value;                        if (provider.GetService(typeof(IConfiguration)) is IConfiguration configService)                        {                            var pathValue = configService.GetSection(value).Value;                            if (pathValue != null)                            {                                var pathV = Convert.ChangeType(pathValue, info.PropertyType);                                info.SetValue(proxy, pathV);                            }                        }                    }                }                return proxy;            };            var serviceDescriptor = new ServiceDescriptor(serviceType, Factory, lifetime);            services.Add(serviceDescriptor);            return services;        }        /// <summary>        /// 添加summer boot扩展        /// </summary>        /// <param name="builder"></param>        /// <returns></returns>        public static IMvcBuilder AddSB(this IMvcBuilder builder)        {            if (builder == null)                throw new ArgumentNullException(nameof(builder));            ControllerFeature feature = new ControllerFeature();            builder.PartManager.PopulateFeature<ControllerFeature>(feature);            foreach (Type type in feature.Controllers.Select<TypeInfo, Type>((Func<TypeInfo, Type>)(c => c.AsType())))                builder.Services.TryAddTransient(type, type);            builder.Services.Replace(ServiceDescriptor.Transient<IControllerActivator, SbControllerActivator>());            return builder;        }        public static IServiceCollection AddSbRepositoryService(this IServiceCollection services, params Type[] interceptorTypes)        {            var types = AppDomain.CurrentDomain.GetAssemblies().SelectMany(it => it.GetTypes());            var tableType = types.Where(it => it.GetCustomAttribute<TableAttribute>() != null);            foreach (var type in tableType)            {                var injectServiceType = typeof(IRepository<>).MakeGenericType(type);                var injectImplType = typeof(BaseRepository<>).MakeGenericType(type);                services.AddSbScoped(injectServiceType, injectImplType, interceptorTypes);            }            return services;        }        /// <summary>        /// 瞬时        /// </summary>        /// <typeparam name="TService"></typeparam>        /// <typeparam name="TImplementation"></typeparam>        /// <param name="services"></param>        /// <param name="name"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbTransient<TService, TImplementation>(this IServiceCollection services, string name = "", params Type[] interceptorTypes)        {            return services.AddSbService(typeof(TService), typeof(TImplementation), ServiceLifetime.Transient, name, interceptorTypes);        }        /// <summary>        /// 瞬时        /// </summary>        /// <param name="services"></param>        /// <param name="serviceType"></param>        /// <param name="implementationType"></param>        /// <param name="name"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbTransient(this IServiceCollection services, Type serviceType,            Type implementationType, string name = "", params Type[] interceptorTypes)        {            return services.AddSbService(serviceType, implementationType, ServiceLifetime.Transient, name, interceptorTypes);        }        /// <summary>        /// 请求级别        /// </summary>        /// <typeparam name="TService"></typeparam>        /// <typeparam name="TImplementation"></typeparam>        /// <param name="services"></param>        /// <param name="name"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbScoped<TService, TImplementation>(this IServiceCollection services, string name = "", params Type[] interceptorTypes)        {            return services.AddSbService(typeof(TService), typeof(TImplementation), ServiceLifetime.Scoped, name, interceptorTypes);        }        /// <summary>        /// 请求级别        /// </summary>        /// <param name="services"></param>        /// <param name="serviceType"></param>        /// <param name="implementationType"></param>        /// <param name="name"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbScoped(this IServiceCollection services, Type serviceType,            Type implementationType, string name = "", params Type[] interceptorTypes)        {            return services.AddSbService(serviceType, implementationType, ServiceLifetime.Scoped, name, interceptorTypes);        }        /// <summary>        /// 单例        /// </summary>        /// <typeparam name="TService"></typeparam>        /// <typeparam name="TImplementation"></typeparam>        /// <param name="services"></param>        /// <param name="name"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbSingleton<TService, TImplementation>(this IServiceCollection services, string name = "", params Type[] interceptorTypes)        {            return services.AddSbService(typeof(TService), typeof(TImplementation), ServiceLifetime.Singleton, name, interceptorTypes);        }        /// <summary>        /// 单例        /// </summary>        /// <param name="services"></param>        /// <param name="serviceType"></param>        /// <param name="implementationType"></param>        /// <param name="name"></param>        /// <param name="interceptorTypes"></param>        /// <returns></returns>        public static IServiceCollection AddSbSingleton(this IServiceCollection services, Type serviceType,            Type implementationType, string name = "", params Type[] interceptorTypes)        {            return services.AddSbService(serviceType, implementationType, ServiceLifetime.Singleton, name, interceptorTypes);        }        public static IServiceCollection AddSbService(this IServiceCollection services, Type serviceType, Type implementationType,            ServiceLifetime lifetime, string name = "", params Type[] interceptorTypes)        {            services.Add(new ServiceDescriptor(implementationType, implementationType, lifetime));            object Factory(IServiceProvider provider)            {                var target = provider.GetService(implementationType);                var properties = implementationType.GetTypeInfo().DeclaredProperties;                foreach (PropertyInfo info in properties)                {                    //属性注入                    if (info.GetCustomAttribute<AutowiredAttribute>() != null)                    {                        var propertyType = info.PropertyType;                        object impl = null;                        var qualifierAttribute = info.GetCustomAttribute<QualifierAttribute>();                        if (qualifierAttribute != null)                        {                            var serviceName = qualifierAttribute.Name;                            var implList = provider.GetServices(propertyType);                            foreach (var tmpImpl in implList)                            {                                if (ProxyUtil.IsProxy(tmpImpl))                                {                                    var addition = tmpImpl as IDependencyAddition;                                    if (addition?.Name == serviceName)                                    {                                        impl = tmpImpl;                                        break; ;                                    }                                }                            }                        }                        else                        {                            impl = provider.GetService(propertyType);                        }                        if (impl != null)                        {                            info.SetValue(target, impl);                        }                    }                    //配置值注入                    if (info.GetCustomAttribute<ValueAttribute>() is ValueAttribute valueAttribute)                    {                        var value = valueAttribute.Value;                        if (provider.GetService(typeof(IConfiguration)) is IConfiguration configService)                        {                            var pathValue = configService.GetSection(value).Value;                            if (pathValue != null)                            {                                var pathV = Convert.ChangeType(pathValue, info.PropertyType);                                info.SetValue(target, pathV);                            }                        }                    }                }                List<IInterceptor> interceptors = interceptorTypes.ToList()                    .ConvertAll<IInterceptor>(interceptorType => provider.GetService(interceptorType) as IInterceptor);                var proxyGenerator = provider.GetService<ProxyGenerator>();                var options = new ProxyGenerationOptions();                options.AddMixinInstance(new DependencyAddition() { Name = name });                var proxy = proxyGenerator.CreateInterfaceProxyWithTarget(serviceType, target, options, interceptors.ToArray());                return proxy;            };            var serviceDescriptor = new ServiceDescriptor(serviceType, Factory, lifetime);            services.Add(serviceDescriptor);            return services;        }    }

修改第一篇中自定义的控制器激活类SbControllerActivator，添加支持[QualifierAttribute]注解的逻辑。

 public class SbControllerActivator : IControllerActivator    {        /// <inheritdoc />        public object Create(ControllerContext actionContext)        {            if (actionContext == null)                throw new ArgumentNullException(nameof(actionContext));            Type serviceType = actionContext.ActionDescriptor.ControllerTypeInfo.AsType();            var target = actionContext.HttpContext.RequestServices.GetRequiredService(serviceType);            var properties = serviceType.GetTypeInfo().DeclaredProperties;            var proxyGenerator = actionContext.HttpContext.RequestServices.GetService<ProxyGenerator>();            var proxy = proxyGenerator.CreateClassProxyWithTarget(serviceType, target);            foreach (PropertyInfo info in properties)            {                //属性注入                if (info.GetCustomAttribute<AutowiredAttribute>() != null)                {                    var propertyType = info.PropertyType;                    object impl = null;                    var qualifierAttribute = info.GetCustomAttribute<QualifierAttribute>();                    if (qualifierAttribute != null)                    {                        var serviceName = qualifierAttribute.Name;                        var implList = actionContext.HttpContext.RequestServices.GetServices(propertyType);                        foreach (var tmpImpl in implList)                        {                            if (ProxyUtil.IsProxy(tmpImpl))                            {                                var addition = tmpImpl as IDependencyAddition;                                if (addition?.Name == serviceName)                                {                                    impl = tmpImpl;                                    break; ;                                }                            }                        }                    }                    else                    {                        impl = actionContext.HttpContext.RequestServices.GetService(propertyType);                    }                    if (impl != null)                    {                        info.SetValue(proxy, impl);                    }                }                //配置值注入                if (info.GetCustomAttribute<ValueAttribute>() is ValueAttribute valueAttribute)                {                    var value = valueAttribute.Value;                    if (actionContext.HttpContext.RequestServices.GetService(typeof(IConfiguration)) is IConfiguration configService)                    {                        var pathValue = configService.GetSection(value).Value;                        if (pathValue != null)                        {                            var pathV = Convert.ChangeType(pathValue, info.PropertyType);                            info.SetValue(proxy, pathV);                        }                    }                }            }            return proxy;        }        /// <inheritdoc />        public virtual void Release(ControllerContext context, object controller)        {        }    }

修改Startup.cs类里的ConfigureServices方法，可以看到，我们在注册WheelA和WheelB的时候，为服务添加了名称，并且随手添加了个拦截器，代码如下:

 public void ConfigureServices(IServiceCollection services)        {            services.Configure<CookiePolicyOptions>(options =>            {                // This lambda determines whether user consent for non-essential cookies is needed for a given request.                options.CheckConsentNeeded = context => true;                options.MinimumSameSitePolicy = SameSiteMode.None;            });            services.AddMvc()                .SetCompatibilityVersion(CompatibilityVersion.Version_2_1)                .AddSB();            services.AddSingleton<ProxyGenerator>();            services.AddSbScoped<Engine>(typeof(TransactionalInterceptor));            services.AddSbScoped<IUnitOfWork, UnitOfWork>();            services.AddScoped(typeof(TransactionalInterceptor));            services.AddSbScoped<ICar, Car>(typeof(TransactionalInterceptor));            services.AddSbScoped<IDbFactory, DbFactory>();            services.AddSbRepositoryService(typeof(TransactionalInterceptor));            services.AddSbScoped<IAddOilService, AddOilService>(typeof(TransactionalInterceptor));            services.AddSbScoped<IWheel, WheelA>("A轮胎", typeof(TransactionalInterceptor));            services.AddSbScoped<IWheel, WheelB>("B轮胎", typeof(TransactionalInterceptor));        }

控制器类HomeController，代码如下：

public class HomeController : Controller    {        [Autowired]        public ICar Car { set; get; }        [Autowired]        public IDistributedCache Cache { set; get; }        [Value("description")]        public string Description { set; get; }        [Autowired]        public IAddOilService AddOilService { set; get; }        public IActionResult Index()        {            var car = Car;            AddOilService.AddOil();            Car.Fire();            Console.WriteLine(Description);            return View();        }    }

核心原理，从SummerBootExtentions类完整源码里单独抽取mixin服务注册和属性注入的代码，可以看到在生成动态代理的时候，在option里添加了mixin实例，也就是我们自定义的DependencyAddition，里面包含了这个服务的名称，在注入时，判断是否有[QualifierAttribute]注解，如果有，就获取整个接口的实现类列表，在循环里，判断是否为动态代理类，如果是，就把每个类实例强转为附加类接口IDependencyAddition，然后获取名称，如果名称和我们[QualifierAttribute]注解指定的名称相同，则注入。

 var proxyGenerator = provider.GetService<ProxyGenerator>();                var options = new ProxyGenerationOptions();                options.AddMixinInstance(new DependencyAddition() { Name = name });                var proxy = proxyGenerator.CreateInterfaceProxyWithTarget(serviceType, target, options, interceptors.ToArray());

//属性注入                    if (info.GetCustomAttribute<AutowiredAttribute>() != null)                    {                        var propertyType = info.PropertyType;                        object impl = null;                        var qualifierAttribute = info.GetCustomAttribute<QualifierAttribute>();                        if (qualifierAttribute != null)                        {                            var serviceName = qualifierAttribute.Name;                            var implList = provider.GetServices(propertyType);                            foreach (var tmpImpl in implList)                            {                                if (ProxyUtil.IsProxy(tmpImpl))                                {                                    var addition = tmpImpl as IDependencyAddition;                                    if (addition?.Name == serviceName)                                    {                                        impl = tmpImpl;                                        break; ;                                    }                                }                            }                        }                        else                        {                            impl = provider.GetService(propertyType);                        }                        if (impl != null)                        {                            info.SetValue(target, impl);                        }                    }

2.效果图

先注入A轮胎

从上图可以看到，生成的动态代理类里包含了Name这个属性，并且名称为A轮胎。

控制台输出，也显示了“我是A轮胎，我正在滚”，符合预期。

注入B轮胎

从上图可以看到，生成的动态代理类里包含了Name这个属性，并且名称为B轮胎。

控制台输出，也显示了“我是B轮胎，我正在滚”，符合预期。

3. 写在最后

通过[Autowired]注解和[Qualifier("B轮胎")]注解联合使用，我们就实现了一个接口多个实现类的精准属性注入，代码看起来是不是舒服多了呢~，我始终相信，如果一件事我讲的别人听不明白，那一定是我讲的不够有趣，不够通俗易懂，所以大白话是必须的，如果文章还有哪里说得太深奥，欢迎给我指出来，同时net core里还有啥功能让你觉得用起来特别别扭的，请！一定！告诉我！，i will try it，因为这特别有趣，因为我一直践行的编程理念就是万物靠注入，万物可拦截，万物皆注解，始终相信IOC和AOP是构建软件的基石，哈哈哈哈哈。

原文来源：博客园

原文地址：

本文地址：http://www.longkongtuishu.com/cabe0A2sBBVoBAVw.html

标签： #net 开发接口 #net接口和类的区别 #net40dynamic