asp.net Core 依赖注入常用获取服务的3种方法

先看简单的demo代码：

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading.Tasks;
using WebApplication1.Models;

namespace WebApplication1.Controllers
{
    public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;
        private readonly IHostEnvironment _hostEnvironment;
        public HomeController(ILogger<HomeController> logger,IHostEnvironment hostEnvironment)
        {
            _logger = logger;
 _hostEnvironment = hostEnvironment;
        }

        public IActionResult Index([FromServices] IHostEnvironment hostEnvironment)
        {
            //1、通过构造函数注入，获取值
            string path = _hostEnvironment.ContentRootPath;

            //2、通过方法的FromServices注入进来，获取值
            string path2 = hostEnvironment.ContentRootPath;

            //通过GetRequiredService来检索服务
            var hostEnvironment2 = HttpContext.RequestServices.GetRequiredService<IHostEnvironment>();
            string path3= hostEnvironment2.ContentRootPath; 

          



            return View();
        }
 
    }
}

 1、通过构造函数注入，获取值

 2、通过方法的FromServices注入进来，获取值

 3、通过GetRequiredService来检索服务