你好，我想請問ASP.NET MVC的模型驗證寫法這樣是否有誤
測試過後發現ModelState.IsValid不管怎樣都會是True
DisplayName則是能正常顯示
程式碼如下
謝謝，新年快樂!

namespace _1119Work.Models
{
    using System;
    using System.Collections.Generic;

    using System.ComponentModel;
    using System.ComponentModel.DataAnnotations;

    public partial class Member
    {
        [DisplayName("密碼")]
        [StringLength(maximumLength:8,ErrorMessage = "密碼長度勿超過8個字元")] 
        public string Mem_password { get; set; }
    }    
}    

namespace _1119Work.Controllers
{
    public class HomeController : Controller
    {
            public ActionResult CreateMember()
            {
                return View();
            }

            [HttpPost]
            public ActionResult CreateMember(string Mem_password)
            {
                if(ModelState.IsValid)
                {
                    return Content("驗證通過");
                }
                return Content("驗證不通過");
            }
    }
}

<div class="form-group">
            @Html.LabelFor(Model => Model.Mem_password, new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Mem_password, new { htmlAttributes = new { @class = "form-control",type = "password"} })
                @Html.ValidationMessageFor(model => model.Mem_password, "", new { @class = "text-danger" })
            </div>
</div>