services.AddSingleton<IApplicationService,ApplicationService>

services.AddScoped<IApplicationService,ApplicationService>

services.AddTransient<IApplicationService,ApplicationService>

    /// <summary>
    /// 用户接口
    /// </summary>
    public interface IUserService
    {
        string GetName();
    }

    /// <summary>
    /// 用户实现
    /// </summary>
    public class UserService : IUserService
    {
        public string GetName()
        {
            return "AZRNG";
        }
    }

        private readonly IUserService _userService;

        public UserController(IUserService userService)
        {
            _userService = userService;
        }

        [HttpGet]
        public ActionResult GetName()
        {
            return Ok(_userService.GetName());
        }
FromServices操作注入
        [HttpGet]
        public ActionResult GetName([FromServices] IUserService _userService)
        {
            return Ok(_userService.GetName());
        }

public void ConfigureServices(IServiceCollection services)
{
    //将服务生命期的范围限定为单个请求的生命期
    services.AddTransient<IUserService, UserService>();
}

        private readonly IUserService _userService;
        public HomeController(IUserService userService)
        {
            _userService = userService;
        }

        public IActionResult Index()
        {
            var info = _userService.GetInfo();
            return View();
        }

        private readonly IServiceProvider _service;
        public UserController(IServiceProvider service)
        {
            _service = service;
        }

        [HttpGet]
        public ActionResult GetName()
        {
            var _userService = (IUserService)_service.GetService(typeof(IUserService));
            return Ok(_userService.GetName());
        }

var provider = services.BuildServiceProvider();
var userserivce = provider.GetService<IUserService>();
//或
var userservice2 = provider.GetRequiredService<IUserService>();