IOC高级玩法-注入多个实现

关于策略模式下需要用到一个接口多个实现的方案

https://www.jianshu.com/p/0753de68244c

此链接是策略模式的案例，讲述多个优惠策略实现同一个接口的应用场景

我们需要用到DI的高级玩法：

在接口定义方法标识

优惠策略接口抽象出一个方法Get() 获取优惠，优惠的实现有很多，我们需要在Startup注入所有的优惠策略的实现

    public interface IActivitiesStrategy
    {
        string Realize { get; }
        /// <summary>
        /// 获取则扣策略
        /// </summary>
        /// <returns></returns>
        double GetDiscountStrategy();
    }

在优惠策略的具体实现上写出方法标识

    public class DoubleElevenActivities : IActivitiesStrategy
    {
        public string Realize => "双十一优惠";

        public double GetDiscountStrategy()
        {
            return 0.11;
        }
    }

    public class DoubleTwelveActivities : IActivitiesStrategy
    {
        public string Realize => "双十二优惠";

        public double GetDiscountStrategy()
        {
            return 0.12;
        }
    }

注册所有方法

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddTransient<IActivitiesStrategy, DoubleElevenActivities>();
            services.AddTransient<IActivitiesStrategy, DoubleTwelveActivities>();
            services.AddMvc();
        }

在使用时候判断使用什么策略

    public class ValuesController : ControllerBase
    {
        private readonly IEnumerable<IActivitiesStrategy> _activitiesStrategy;

        public ValuesController(IEnumerable<IActivitiesStrategy> activitiesStrategy)
        {
            _activitiesStrategy = activitiesStrategy;
        }

        
        // GET api/values
        [HttpGet]
        public ActionResult<double> Get(string tag)
        {
            var method = _activitiesStrategy.Where(x => x.Realize == tag).FirstOrDefault();

            if (method != null)
            {
                return method.GetDiscountStrategy();
            }

            return 1;
        }
    }