Question

我是ASP MVC的初学者，经过SO的大量帮助后，我正在通过ViewModels进步。但是，使用ViewModel，我遇到了以下错误。

给出以下视图：

@model November.ViewModels.Staff_Salutation_VM

//...

using (Html.BeginForm("UpdateStaff", "Settings", FormMethod.Post, 
    new { @class = "clearfix parameter-form update-parameter update-staff", enctype = "multipart/form-data" }))
{
    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)

    //...       

    @for (int i = 0; i < Model.AvailableStaffMembers.Count; i++)
    {
        var staff = Model.AvailableStaffMembers[i];
        <tr>               
            <td>@Html.HiddenFor(model => staff.ID)@Html.ValueFor(model => staff.ID)</td>
            <td>
                @Html.DropDownListFor(  
                    model => model.SalutationID, Model.AvailableSalutations.Select(option => new SelectListItem 
                        {
                            Text = option.Desc.ToString(),
                            Value = option.ID.ToString(),
                            Selected = (option.ID.ToString() == staff.SalutationID.ToString())
                        }
                    ), 
                "Choose...")
            </td>
            <td>@Html.EditorFor(model => staff.FName)</td>
            <td>@Html.EditorFor(model => staff.LName)</td>
            <td>@Html.EditorFor(model => staff.Active)</td>
            <td><a href="/Settings/DeleteStaff?id=@Html.ValueFor(model => staff.ID)">Delete</a></td>
        </tr>
    }

以及以下控制器：

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;
 using System.Web.Mvc;
 using November.Models;
 using November.ViewModels;
 using November.DAL;   

 //...

 //GET
 var staffCreateViewModel = new Staff_Salutation_VM();

 staffCreateViewModel.AvailableSalutations = new List<Prm_Salutation>();
 var activeSalts = (from a in db.Prm_Salutations
                     where a.Active == true
                     orderby a.Desc ascending
                     select a);
 staffCreateViewModel.AvailableSalutations = activeSalts.ToList();

 staffCreateViewModel.AvailableStaffMembers = new List<Prm_Staff>();
 var activeStaff = (from a in db.Prm_Staffs
                     where a.Active == true
                     orderby a.LName ascending
                     select a);
 staffCreateViewModel.AvailableStaffMembers = activeStaff.ToList();

 return View("StaffMembers", staffCreateViewModel);



 //POST
 public ActionResult UpdateStaff(Staff_Salutation_VM list)
 {
      if (ModelState.IsValid)
      {
           foreach (var formData in list) //no longer works due to dropping List<>
           {
                var tbl = db.Prm_Staffs.Where(a => a.ID.Equals(formData.ID)).FirstOrDefault();
                if (tbl != null)
                {
                     var Prm_StaffModel = new Prm_Staff();

                     Prm_StaffModel.SalutationID = formData.SalutationID;
                     Prm_StaffModel.FName = formData.FName;
                     Prm_StaffModel.LName = formData.LName;
                     Prm_StaffModel.Active = formData.Active;
                }
           }
           db.SaveChanges();
           ViewBag.UpdateRtrn = "Successfully Updated.";
           return RedirectToAction("Parameters", new { param = "Staff Members" });
      }
      else
           {
                ViewBag.UpdateRtrn = "Failed ! Please try again.";
                return RedirectToAction("Parameters", new { param = "Staff Members" });
           }
      }
      return RedirectToAction("Parameters", new { param = "Staff Members" });
 }

并且，为了更好的衡量，ViewModel本身：

 public class Staff_Salutation_VM
 {
      public int ID { get; set; }
      public int SalutationID { get; set; }
      public string FName { get; set; }
      public string LName { get; set; }
      public bool Active { get; set; }

      public List<Prm_Salutation> AvailableSalutations { get; set; }
      public List<Prm_Staff> AvailableStaffMembers { get; set; }

      public Staff_Salutation_VM() { }        
 }

触发时，没有任何表单值填充ActionResult，导致在达到Object reference not set to an instance of an object.行时抛出foreach (var formData in list)异常。调试显示list为空。怎么会这样呢？或者说，我做错了什么？

编辑：我的POST list中的ActionResult变量现在正在获取数据 - 或者至少在调试时显示了类中的各种类型。然后我如何迭代它以将数据保存在DB的适当行中？

Answer 1

我完全错过了方法签名，对不起！您的初始视图加载会传递模型Staff_Salutation_VM，但您的UpdateStaff（已发布表单）需要List<Staff_Salutation_VM>。这些是不同的动物。将public ActionResult UpdateStaff(List<Staff_Salutation_VM> list)更改为public ActionResult UpdateStaff(Staff_Salutation_VM staff)只是为了查看您是否超过null ref例外。请注意，由于您没有进入IEnumerable，因此您需要删除您的foreach。

Answer 2

我希望这篇文章对你有所帮助。 Model Binding To A List

ASP MVC查看将null发布到Controller

2 个答案: