.NET7 中Autofac依赖注入整合多层，项目中可直接用

一、配置Autofac替换内置DI

1.安装Nuget包：Autofac.Extensions.DependencyInjection

2.Program.cs中加上

builder.Host.UseServiceProviderFactory(new AutofacServiceProviderFactory());
builder.Host.ConfigureContainer<ContainerBuilder>(containerBuilder =>
{
    //在这里写注入代码

});

二、构造函数注入

新建IUserService，类UserService

 public interface IUserService
    {
        public string GetUserName();
    }

 public class UserService：IUserService
    {
        public string GetUserName()
        {
            return "张三";
        }
    }

在上面的ConfigureContainer方法把UserService注入进来，默认是瞬时注入

瞬时注入：containerBuilder.RegisterType<UserService>().As<IUserService>().InstancePerDependency();;

单例注入：containerBuilder.RegisterType<UserService>().As<IUserService>().SingleInstance();

生命周期注入： containerBuilder.RegisterType<UserService>().As<IUserService>().InstancePerLifetimeScope();

注入试下是否注入成功

调用成功，证明注入成功

三、属性注入

1.把HomeController改成属性注入形式，属性注入有一个问题，就是那些属性需要注入？全部注入没必要，父类也有很多属性，要按需注入，给属性增加一个自定义特性标识说明需要注入。

public class HomeController : Controller
    {
        [AutowiredProperty]
        private IUserService userService { get; set; }
        public IActionResult Index()
        {
            string name = userService.GetUserName();
              return View();
        }
    }

2.新增自定义特性类AutowiredPropertyAttribute.cs

[AttributeUsage(AttributeTargets.Property)]//为了支持属性注入，只能打到属性上
    public class AutowiredPropertyAttribute: Attribute
    {
    }

3.增加识别特性类AutowiredPropertySelector.cs

public class AutowiredPropertySelector : IPropertySelector
    {
        public bool InjectProperty(PropertyInfo propertyInfo, object instance)
        {
            //判断属性的特性是否包含自定义的属性,标记有返回true
            return propertyInfo.CustomAttributes.Any(s => s.AttributeType == typeof(AutowiredPropertyAttribute));
        }
    }

4.因为Controller 默认是由 Mvc 模块管理的，需要把控制器放到IOC容器中，在Program.cs中增加

//让控制器实例由容器创建
builder.Services.Replace(ServiceDescriptor.Transient<IControllerActivator, ServiceBasedControllerActivator>());

5.把容器注册到IOC容器，在Program.cs的ConfigureContainer()增加

 //获取所有控制器类型并使用属性注入
    Type[] controllersTypeAssembly = typeof(Program).Assembly.GetExportedTypes()
        .Where(type => typeof(ControllerBase).IsAssignableFrom(type)).ToArray();
    containerBuilder.RegisterTypes(controllersTypeAssembly).PropertiesAutowired(new AutowiredPropertySelector());

验证：

成功。

四、批量注入

实际项目中那么多需要注入的类，一个个写注册就不太现实了，需要一个可以批量注入的方法。

1.新建三个空接口IScopeDenpendency.cs，ISingletonDenpendency.cs，ITransitDenpendency.cs

/// <summary>
    /// 瞬时注入
    /// </summary>
    public interface ITransitDenpendency
    {
    }
　　/// <summary>
    /// 单例注入标识
    /// </summary>
    public interface ISingletonDenpendency
    {
    }
　　 /// <summary>
    /// 生命周期注入标识
    /// </summary>
    public interface IScopeDenpendency
    {
    }

2.把上面要注入的类实现上面的接口

3.新增一个IocManager类

/// <summary>
    /// Ioc管理
    /// </summary>
    public static class IocManager
    {
        /// <summary>
        /// 批量注入扩展
        /// </summary>
        /// <param name="builder"></param>
        /// <param name="assembly"></param>
        public static void BatchAutowired(this ContainerBuilder builder, Assembly assembly)
        {

            var transientType = typeof(ITransitDenpendency); //瞬时注入
            var singletonType = typeof(ISingletonDenpendency); //单例注入
            var scopeType = typeof(IScopeDenpendency); //单例注入
            //瞬时注入
            builder.RegisterAssemblyTypes(assembly).Where(t => t.IsClass && !t.IsAbstract && t.GetInterfaces().Contains(transientType))
                .AsSelf()
                .AsImplementedInterfaces()
                .InstancePerDependency()
                .PropertiesAutowired(new AutowiredPropertySelector());
            //单例注入
            builder.RegisterAssemblyTypes(assembly).Where(t => t.IsClass && !t.IsAbstract && t.GetInterfaces().Contains(singletonType))
               .AsSelf()
               .AsImplementedInterfaces()
               .SingleInstance()
               .PropertiesAutowired(new AutowiredPropertySelector());
            //生命周期注入
            builder.RegisterAssemblyTypes(assembly).Where(t => t.IsClass && !t.IsAbstract && t.GetInterfaces().Contains(scopeType))
               .AsSelf()
               .AsImplementedInterfaces()
               .InstancePerLifetimeScope()
               .PropertiesAutowired(new AutowiredPropertySelector());

        }

4.把注入类ConfigureContainer改成

5.防止Program.cs代码过多，建一个Module把注入代码搬走，新建AutofacRegisterModule.cs类把ConfigureContainer的代码移过去

  public class AutofacRegisterModule : Autofac.Module
    {
        protected override void Load(ContainerBuilder builder)
        {

            //获取所有控制器类型并使用属性注入
            Type[] controllersTypeAssembly = typeof(Program).Assembly.GetExportedTypes()
                .Where(type => typeof(ControllerBase).IsAssignableFrom(type)).ToArray();
            builder.RegisterTypes(controllersTypeAssembly).PropertiesAutowired(new AutowiredPropertySelector());
            //批量自动注入,把需要注入层的程序集传参数,注入Service层的类
            builder.BatchAutowired(typeof(UserService).Assembly);
            //注入其它层的containerBuilder.BatchAutowired(typeof(其它层的任务一个类).Assembly);
        }
    }

ConfigureContainer的代码变成

五、手动获取实例

手动获取实例的场景有静态帮助类中获取实例，例如redisHelper中获取注入的配置文件中的连接字符串

1.在上面的IocManager类中增加

 private static object obj = new object();
 private static ILifetimeScope _container { get; set; }

  public static void InitContainer(ILifetimeScope container)
        {
            //防止过程中方法被调用_container发生改变
            if (_container == null)
            {
                lock (obj)
                {
                    if (_container == null)
                    {
                        _container = container;
                    }
                }
            }
        }
        /// <summary>
        /// 手动获取实例
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <returns></returns>
        public static T Resolve<T>()
        {
            return _container.Resolve<T>();
        }

2.在Program.cs中增加

3.验证，新建一个DataHelper.cs类

 public class DataHelper
    {
        //手动注入UserService
        private static IUserService userService = IocManager.Resolve<IUserService>();
        public static string GetData()
        {
            return userService.GetUserName();
        }
    }

成功获取到值，证明从容器中获取成功。

六、其它用法

1.不用接口，直接注入实例

 public class UserService :ITransitDenpendency
    {
        public string GetUserName()
        {
            return "张三";
        }
    }

2.一接口多实现

 public class UserService :IUserService
    {
        public string GetUserName()
        {
            return "张三";
        }
    }

 public class UserService2 : IUserService
    {
        public string GetUserName()
        {
            return "张三2号";
        }
    }

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