.Net Core3.1 Autofac实现构造函数依赖注入

1、通过nuget下载安装如下截图所示的Nuget程序包

 2、如下所示,修改Progam中的CreateHostBuilder方法，使用autofac的容器工厂替换系统默认的容器：

 public class Program
    {
        /// <summary>
        /// 
        /// </summary>
        /// <param name="args"></param>
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        /// <summary>
        /// 
        /// </summary>
        /// <param name="args"></param>
        /// <returns></returns>
        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
            .UseServiceProviderFactory(new AutofacServiceProviderFactory()) //使用autofac的容器工厂替换系统默认的容器
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                }).UseNLog();  //使用NLog
    }

3、在Startup类中增加一个方法ConfigureContainer，配置Auto fac Container

 /// <summary>
        /// Autofac动态注入所有含有 [Services]标签的服务
        /// </summary>
        /// <param name="builder"></param>
        public void ConfigureContainer(ContainerBuilder builder)
        {
            builder.RegisterAssemblyTypes(DependencyUtilities.GetReferencedAssemblies())
                         .Where(type => type.GetCustomAttribute<ServicesAttribute>() != null)
                         .AsImplementedInterfaces()
                         .AsSelf()
                         .InstancePerLifetimeScope();

        }

4、定义一个标记性特性类  【ServicesAttribute】

namespace NetCoreWebApi.Repository.DependencyAttribute
{
    /// <summary>
    /// 自定义依赖注入自定义特性
    /// </summary>
    [AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = false)]
    public class ServicesAttribute:Attribute
    {
    }
}

5、 利用反射加载需要注入的dll程序集

    public static class DependencyUtilities
    {
        const string pattern = "^Microsoft.\\w*|^System.\\w*|^Newtonsoft.\\w*|^Autofac.\\w*|^Serilog.\\w*|^App.\\w*|^runtime.\\w*|^Google.\\w*|^IdentityServer4.\\w*";

        public static Assembly[] GetReferencedAssemblies()
        {
            Regex relatedRegex = new Regex(pattern, RegexOptions.Singleline | RegexOptions.Compiled | RegexOptions.IgnoreCase);
            return DependencyContext.Default.RuntimeLibraries
                 .Where(item => !relatedRegex.IsMatch(item.Name))
                 .SelectMany(item => item.GetDefaultAssemblyNames(DependencyContext.Default))
                 .Select(item => Assembly.Load(item))
                 .ToArray();
        }
    }

6、从加载的程序集中获取到含有 [Services]标签的程序集，然后创建对象

 /// <summary>
        /// Autofac动态注入所有含有 [Services]标签的服务
        /// </summary>
        /// <param name="builder"></param>
        public void ConfigureContainer(ContainerBuilder builder)
        {
            builder.RegisterAssemblyTypes(DependencyUtilities.GetReferencedAssemblies())
                         .Where(type => type.GetCustomAttribute<ServicesAttribute>() != null)
                         .AsImplementedInterfaces()
                         .AsSelf()
                         .InstancePerLifetimeScope();

        }

7、依赖构造函数注入实例代码如下

[Route("api/[controller]/[Action]")]
    [ApiController]
    // [RequestFilter] 不能直接放置在这，原因RequestFilter过滤器中需要注入ILogger
    [TypeFilter(typeof(RequestFilterAttribute))]

    public class SystemMembersController : BaseController
    {
        private readonly ILogger<SystemMembersController> _logger;
        private readonly SystemLogServices _systemLogServices;

        /// <summary>
        /// 1、该类依赖 SystemLogServices 类，所以在SystemLogServices类上面需要标记自定义的标记注入特性 [Services]
        /// 2、AutoFac 通过识别特性动态注入含有[service]标签的服务
        /// </summary>
        /// <param name="logger"></param>
        /// <param name="systemLogServices"></param>
        public SystemMembersController(ILogger<SystemMembersController> logger, SystemLogServices systemLogServices)
        {
            _logger = logger;
            _systemLogServices = systemLogServices;
        }
        /// <summary>
        /// 测试IOC依赖注入
        /// </summary>
        [HttpGet]
        public void TestIOC()
        {
            _systemLogServices.InsertLog();
        }
    }

namespace NetCoreWebApi.Services.Services.SystemLog
{
    [Services]
    public class SystemLogServices
    {
        private readonly Ofcp_Log_GlobalLogRepository _Log_GlobalLogRepository;
        private readonly ILogger<SystemLogServices> _logger;

        /// <summary>
        /// 该类又依赖于Ofcp_Log_GlobalLogRepository，所以在该类又依赖于Ofcp_Log_GlobalLogRepository类上面需要标记自定义的标记注入特性 [Services]
        /// </summary>
        /// <param name="log_GlobalLogRepository"></param>
        /// <param name="logger"></param>
        public SystemLogServices(Ofcp_Log_GlobalLogRepository log_GlobalLogRepository, ILogger<SystemLogServices> logger)
        {
            _Log_GlobalLogRepository = log_GlobalLogRepository;
            _logger = logger;
        }

        public void InsertLog()
        {
            try
            {
                var Log = new Marketing_Log_ProcessUpdate
                {
                    Guid = Guid.NewGuid().ToString(),
                    ApiUrl = "api/InsertLog",
                    Extension = "InsertLog日志测试"

                };
                _Log_GlobalLogRepository.Client.Insertable<Ofcp_Log_GlobalLog>(Log).IgnoreColumns(true,false).ExecuteCommand();
            }
            catch (Exception ex)
            {
                _logger.LogError("InsertLog写入失败", ex.Message);
            }
        }
       
    }
}

namespace NetCoreWebApi.Repository.Respository
{
    /// <summary>
    /// 
    /// </summary>
    [Services] 
    public class Ofcp_Log_GlobalLogRepository:BaseRepository<Ofcp_Log_GlobalLog>
    {
        public Ofcp_Log_GlobalLogRepository(IDbClientFactory clientFactory):base(clientFactory)
        { 
        
        }
    }
}

8、运行结果及测试

1、调用SystemMembersController控制器的TestIOC方法时，由于SystemMembersController控制器依赖于SystemLogServices类，所以程序首先调用SystemLogServices类的构造函数，初始化对象

2、初始化SystemLogServices对象时，检测到SystemLogServices又依赖于Ofcp_Log_GlobalLogRepository。程序调用Ofcp_Log_GlobalLogRepository的构造函数初始化对象

3、所以，在调用SystemMembersController控制器的方法时，程序先构造Ofcp_Log_GlobalLogRepository对象，构造完成后再构造SystemLogServices，最后才构造SystemMembersController