从数据库MVC4获取带有下拉列表的运行时错误

本文关键字：下拉列表 运行时错误 数据库 MVC4 获取 | 更新日期: 2023-09-27 17:57:05

我正试图在MVC4中创建一个下拉列表，该列表源自一个名为"SiteTableBookings"的数据库模型，运行时错误为：

"在App_Web_e3cawdyt.dll中发生类型为System.NullReferenceException的异常，但未在用户代码"中处理

基本上，该应用程序需要一个航班预订的下拉列表，我已经搜索了许多关于如何在线实现下拉列表的方法，但无法运行该应用程序。

MVC4新手，仍在学习任何帮助，将不胜感激。

型号：

public partial class SiteBookingsTable
{
    public int listID { get; set; }
    public string departureAirport { get; set; }  
    public string chooseDepartureAirport { get; set; }     
    public IEnumerable<SiteBookingsTable> selectDeparture = new List<SiteBookingsTable>
    {
        new SiteBookingsTable {listID = 0, departureAirport = "London (LTN)"},
        new SiteBookingsTable {listID = 1, departureAirport = "Manchester (MAN)"}
    };
}

视图：

<tr>
   <td>@Html.LabelFor(model => model.chooseDepartureAirport)<br /> 
       @Html.DropDownListFor(model => model.chooseDepartureAirport,
        new SelectList(Model.selectDeparture, "listID", "departureAirport")) </td>
</tr>

控制器：

public ActionResult Create()
{           
    return View();
}

从数据库MVC4获取带有下拉列表的运行时错误

我会在控制器而不是模型中创建列表。

型号：

public partial class SiteBookingsTable
{
    public int listID { get; set; }
    public string departureAirport { get; set; }  
    public string chooseDepartureAirport { get; set; }     
    public IEnumerable<SelectListItem> selectDeparture { get; set; }
}

视图：

<tr>
   <td>@Html.LabelFor(model => model.chooseDepartureAirport)<br /> 
       @Html.DropDownListFor(model => model.chooseDepartureAirport,
                             Model.selectDeparture)
   </td>
</tr>

控制器：

public ActionResult Create()
{
    IEnumerable<SiteBookingsTable> selectDeparture = new List<SiteBookingsTable>()
    {
        new SiteBookingsTable {listID = 0, departureAirport = "London (LTN)"},
        new SiteBookingsTable {listID = 1, departureAirport = "Manchester (MAN)"}
    };
    model = new SiteBookingsTable()
    model.selectDeparture = new SelectList(selectDeparture, "listID", "departureAirport");
    return View(model);
}

我认为您需要将selectDepartment字段设置为静态字段，如下所示：

public static IEnumerable<SiteBookingsTable> selectDeparture = new List<SiteBookingsTable> 
{ 
    new SiteBookingsTable { listID = 0, departureAirport = "London (LTN)" }, 
    new SiteBookingsTable { listID = 1, departureAirport = "Manchester (MAN)" } 
};

然后更新您的下拉列表以使用此静态属性，并指向departureAirport属性：

@Html.DropDownListFor(model => model.departureAirport,
    new SelectList(SiteBookingsTable.selectDeparture, "listID", "departureAirport"))
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