C#.netmvc单文件上传 ajax上传文件

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Web;

namespace WebApplication1.Models
{
    public class UserInfo
    {
        public string Id { get; set; }
    
        public string UserName { get; set; }
   
        public string Address { get; set; }
  
        public HttpPostedFileBase ImgUrl { get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using WebApplication1.Models;
using System.IO;

namespace WebApplication1.Controllers
{
    public class HomeController : Controller
    {
        [HttpGet]
        public ActionResult Index()
        {
            return View();
        }
        [HttpPost]
        public string Index(HttpPostedFileBase file)
        {
            //判断文件是否存在
            if (file != null)
            {
                //写一个文件保存的路径
                string imgpath = Server.MapPath(@"\Img\");
                //判断路径是否存在,不存在则创建
                if (!Directory.Exists(imgpath))
                {
                    Directory.CreateDirectory(imgpath);
                }
                //给文件再起个名
                string ImgName = DateTime.Now.ToString("yyyyMMddHHmmss")+"_"+file.FileName;
                //把文件保存到服务器上
                file.SaveAs(imgpath + ImgName);
                //返回文件的位置
                return @"\Img\" + ImgName;
            }

            return "null";
        }
    }
}

@{
    ViewBag.Title = "Index";
}

Index
class="form-group">
    for="crowd_file" class="col-sm-2 control-label">上传文件
    
class="col-sm-10">
        "file" accept=".jpg" id="crowd_file">
    

class="form-group">

    
class="col-sm-10">
        "button" value="上传" class="submit" id="crowd_file">