viewModel 中的下拉列表创建视图

Question

我有一个 "Leads" table，它与 "Employees" table 有一对多的关系。我还创建了一个 leadViewModel class 因为我需要一些关于潜在客户的额外信息（比如地址和电话等）

这是领导 class:

public partial class Leads
{
    [Key]
    public int LeadID { get; set; }

    public string FirstName { get; set; }
    public string LastName { get; set; }
    [NotMapped]
    public string FullName { get { return FirstName + " " + LastName; } }

    public int EmployeeID { get; set; }

    public virtual Employees Employees { get; set; }
}

员工Class：

public partial class Employees
{
    public Employees()
    {
        this.Leads = new HashSet<Leads>();
    }

    [Key]
    public int EmployeeID { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    [NotMapped]
    public string FullName { get { return FirstName + " " + LastName; } }

    public virtual ICollection<Leads> Leads { get; set; }
}

leadViewModel:

public class LeadViewModel
{
    public Leads _leads { get; set; }
    public Addresses _addresses { get; set; }
    public Phones _phones { get; set; }
    public Emails _emails { get; set; }

    public IEnumerable<SelectListItem> EmployeesSelectListItem { get; set; }
}

现在我想在 "Create" 视图中有一个下拉列表。我不知道该怎么办。这是我所做的，但出现了错误。

LeadsController 创建获取：

    // GET: Leads/Create
    public ActionResult Create()
    {
        ViewBag.EmployeeID = new SelectList(db.Employees, "EmployeeID", "FirstName");

        return View();
    }

LeadsController 创建 Post:

    [HttpPost]
    [ValidateAntiForgeryToken]        
    public ActionResult Create([Bind(Include = "_leads,_addresses,_phones,_emails,EmployeesSelectListItem")] LeadViewModel leadVM)
    {            
        if (ModelState.IsValid)
        {
            using (TransactionScope leadScope = new TransactionScope())
            {
                db.Leads.Add(leadVM._leads);
                db.SaveChanges();

                leadScope.Complete();

                return RedirectToAction("Index");
            }
        }

        ViewBag.EmployeeID = new SelectList(db.Employees, "EmployeeID", "FirstName", leadVM._leads.EmployeeID);

        return View(leadVM);
    }

最后是创建视图：

@model CL_AHR_CRM.ViewModels.LeadViewModel

...

   <div class="form-group">
        @Html.LabelFor(model => model._leads.EmployeeID, "EmployeeID", htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.DropDownListFor(x => x._leads.EmployeeID, new SelectList(Model.EmployeesSelectListItem, "EmployeeID", "FirstName"), htmlAttributes: new { @class = "form-control" })
            @Html.ValidationMessageFor(model => model._leads.EmployeeID, "", new { @class = "text-danger" })
        </div>
    </div>

我重复我的问题：当使用像这样的 viewModel 时，我如何在视图中使用 dropdownliast，因为显然我所做的不是正确的方式并且不起作用。我收到错误："Object reference not set to an instance of an object." on the Html.DropdownlistFor(...) in create view.

Answer 1

您的视图基于 typeof LeadViewModel 但在 GET 方法中您没有将模型实例传递给视图，更不用说填充 EmployeesSelectListItem 属性所以在您的 DropDownListFor() 方法 new SelectList(Model.EmployeesSelectListItem, ... 将抛出异常（Model 的值是 null

将视图模型属性更改为

public SelectList EmployeesSelectListItem { get; set; } // perhaps rename to EmployeeList?

然后将 GET 方法更改为

public ActionResult Create()
{
  LeadViewModel model = new LeadViewModel();
  model.EmployeesSelectListItem = new SelectList(db.Employees, "EmployeeID", "FirstName");
  return View(model);
}

同样在POST方法中你需要使用

leadVM.EmployeesSelectListItem = new SelectList(db.Employees, "EmployeeID", "FirstName");

当您 return 视图时（即当 ModelState 无效时）

然后在视图中使用

@Html.DropDownListFor(x => x._leads.EmployeeID, Model.EmployeesSelectListItem, new { @class = "form-control" })

viewModel 中的下拉列表创建视图

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