Question

我有地址的控制器我用它来输入多个地址但是我想创建dropdosnlist来选择这个人并输入他的地址我在模型文件夹中创建了这个帮助器类来创建选择项

public class PersonsSelectItems
{
    public int SelectedId { get; set; }
    public List<Person> Persons { get; set; }
}

我使用AddressController将selectitem发送到它的视图

public class AddressController : Controller
    {

        private readonly CustomersDBEntities context = new CustomersDBEntities();
        private PersonsSelectItems personsSelectItems= new PersonsSelectItems();

        ///get list of persones
        /// 
        public List<Person> GetPersonsList()
        {
            return (from c in personsSelectItems.Persons
                    select c).ToList();
        }

        //
        // GET: /Address/

        public ActionResult Index()
        {


            //var model = GetPersonsList(); //var model = GetPersonsList().Select(x => new SelectListItem
            //{
            //    Value = x.PersonID.ToString(),
            //    Text = x.FirstName,
            //    Selected = true | false
            //});

            ///var model = new PersonsSelectItems { Persons = GetPersonsList() };

            var model = GetPersonsList();
            return View(model);
        }

        // 
        // GET: /Address/Welcome/ 

        public string Welcome()
        {
            return "This is the Welcome action method...";
        }

        [HttpPost]
        public ActionResult Create(Address address)
        {
            //Loop through the request.forms

            var Addesslist = new List<Address>();
            for (int i = 1; i <= Request.Form.Count; i++)
            {
                var street = Request.Form["street_0" + i + ""];
                var city = Request.Form["city_0" + i + ""];
                var postalCode = Request.Form["postalCode_0" + i + ""];
                var province = Request.Form["province_0" + i + ""];
                var personID = 1;
                if (street != null && city != null && postalCode != null && province != null)
                {

                    try
                    {
                        context.Addresses.Add(new Address
                        {
                            Street = street,
                            City = city,
                            Province = province,
                            PostalCode = postalCode,
                            PersonID = personID
                        });
                        context.SaveChanges();
                    }
                    catch (Exception exc)
                    {

                    }
                }
                else
                {
                    break;
                }

            }
            return RedirectToAction("Index");
        }
    }

我得到了这个说明

值不能为空。参数名称：source

描述：执行期间发生了未处理的异常   当前的网络请求。请查看堆栈跟踪了解更多信息   有关错误的信息以及它在代码中的起源。

异常详细信息：System.ArgumentNullException：值不能为null。   参数名称：source   地址视图       @model MVC.Models.Address

Tuple<Person,Order>
@{
    ViewBag.Title = "Index";
}

<h2>Index</h2>

@using (Html.BeginForm("Create", "Address", FormMethod.Post))
{

@Html.DropDownListFor(x => x.Person, new SelectList(Model.Person, "PersonId", "FirstName"))



    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)

        <div class="table-responsive">
            <table id="address_table" class="table">
                <thead>
                    <tr>
                        <th>Street</th>
                        <th>City</th>
                        <th>Province</th>
                        <th>PostalCode</th>
                        <th>&nbsp;</th>

                    </tr>
                </thead>
                <tbody>
                    <tr>
                        <td>
                            <input id="Text1" type="text" name="street_01" maxlength="255" required class="street" /></td>
                        <td>
                            <input id="Text2" type="text" name="city_01" maxlength="255" required class="city" /></td>
                        <td>
                            <input id="Text3" type="text" name="province_01" maxlength="255" required class="province" /></td>
                        <td>
                            <input id="Text4" type="text" name="postalCode_01" maxlength="7" required class="postalCode" /></td>
                        <td>&nbsp;</td>
                    </tr>
                </tbody>
            </table>
        </div>
        <input type="button" value="Add Row" id="add_AdressRow" class="btn btn-lg btn-success btn-block" />

        <p>
            <input type="submit" value="Create" />
        </p>

}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

我想问一下如何使用GetPersonsList（）函数中的列表绑定dropDwonList 从AdressController和绑定我现在他们离开了，但我找不到它？

Answer 1

您的问题是您尝试在null列表上使用某些LINQ。

这个坏孩子在这里：

public List<Person> Persons { get; set; }

是null。您可以在类型中添加构造函数来初始化它：

public class PersonsSelectItems
{
    public int SelectedId { get; set; }
    public List<Person> Persons { get; set; }

    public PersonsSelectItems() {
        Persons = new List<Person>();
    }
}

..这将阻止您当前的错误。

我必须指出一些事情。首先，命名Persons很奇怪。使其成为People的英文复数。

其次，你实际上不必在这里使用LINQ。您的GetPersonList方法可以简单地为：

public List<Person> GetPersonsList()
{
    return personsSelectItems.Persons;
}

即便如此......您已经可以访问该集合了。因此，model作业可以是：

var model = _personsSelectItems.Persons;

绑定asp.net MVC4中的下拉列表

1 个答案: