.NetCore的依赖注入

//MVC自带的三种依赖注入方式

        //MVC自带的三种依赖注入方式
        public WeatherForecastController(ILogger<WeatherForecastController> logger, IConfiguration configuration, IHostEnvironment hostEnvironment)
        {
    
            _logger = logger;
            this.configuration = configuration;
            this.hostEnvironment = hostEnvironment;
        }

        [HttpGet]
        public IEnumerable<WeatherForecast> Get()
        {
    
            var rng = new Random();
            //第二种依赖注入方式
            IHostEnvironment host = HttpContext.RequestServices.GetService(typeof(IHostEnvironment)) as IHostEnvironment;
            //第三种依赖注入方式
            var host2 = HttpContext.RequestServices.GetRequiredService<IHostEnvironment>();
            return Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
    
                Date = DateTime.Now.AddDays(index),
                TemperatureC = rng.Next(-20, 55),
                Summary = Summaries[rng.Next(Summaries.Length)]
            })
            .ToArray();
        }

        public void ConfigureServices(IServiceCollection services)
        {
    
            services.AddControllers();
            services.AddSingleton<IServiceCollection>();//每次都是原来的那个
            services.AddScoped<ILogger>(); //本次进入Controller的URL 获取的都是一样的
            services.AddTransient<ILogger>(); //每次都是新的

            services.AddSingleton<IServiceCollection>(x => new ServiceCollection());
            //等同于
            services.AddSingleton<IServiceCollection, ServiceCollection>();

        }