无法将类型 'System.Collections.Generic.List<InventoryLocations>' 隐式转换为 'System.Collections.Generic.IEnumerable<SelectListItem>'

Question

我是初学者。我正在研究这个 ASP.NET Core MVC 项目，我试图通过提交我的 form 将我的 ViewModel 传递给我的 POST 方法，以便我可以将数据保存在 Database。一旦我的 GET 方法完成运行，我就会看到以下内容 RuntimeBinderException:

RuntimeBinderException: Cannot implicitly convert type 'System.Collections.Generic.List' to 'System.Collections.Generic.IEnumerable'. An explicit conversion exists (are you missing a cast?

查看：

<div class="row">
    <div class="col-sm-4">
        <div class="input-group fg-float">
            <div class="fg-line form-chose">
                <label asp-for="LocationName" class="fg-labels" for="locationName"></label>
                    <select asp-for="LocationName" asp-items="ViewBag.Locations" class="chosen disabledropdowncntrl" data-placeholder="Choose a Location" name="locationName" id="dropDownLocationNames">
                        <option value=""></option>
                    </select>
            </div>
        </div>
    </div>
</div>

控制器：

// GET: ~/Inventory/Locate/Id
    public IActionResult Locate(int Id)
    {
        InventoryLocationsHistoryViewModel locationsHistoryVM = new InventoryLocationsHistoryViewModel();

        // Populating Locations DropDownList
        var locationsList = new List<InventoryLocations>();
        locationsList = _context.InventoryLocations.ToList();
        var locations = locationsList.OrderBy(l => l.LocationName).Select(us => new SelectListItem { Value = us.LocationId.ToString(), Text = us.LocationName }).ToList();
        ViewBag.Locations = locationsList;
        ...
        ...
        return View(locationsHistoryVM);
    }

ViewModel:

namespace BackOffice.Models.CustomModels
{
    public class InventoryLocationsHistoryViewModel
    {
        public string UserId { get; set; }
        //public ApplicationUser User { get; set; }

        public string OtherUser { get; set; }
        public string Comments { get; set; }

        public string LocationName { get; set; }
        public InventoryLocations Location { get; set; }

        public DateTime? FromDate { get; set; }
        public DateTime? ToDate { get; set; }
    }
}

我做错了什么？

Answer 1

您 ViewBag.Locations 设置不正确。您还可以折叠很多代码，因为您将整个列表放入内存中进行排序和 select 2 列。这将创建一个 select 语句，仅 select 需要 2 列并在 sql 服务器端执行排序。

// GET: ~/Inventory/Locate/Id
    public IActionResult Locate(int Id)
    {
        InventoryLocationsHistoryViewModel locationsHistoryVM = new InventoryLocationsHistoryViewModel();


        var locations = new SelectList(_context.InventoryLocations.OrderBy(l => l.LocationName)
            .ToDictionary(us => us.LocationId, us => us.LocationName), "Key", "Value");
        ViewBag.Locations = locations;

        ...
        ...
        return View(locationsHistoryVM);
    }

无法将类型 'System.Collections.Generic.List<InventoryLocations>' 隐式转换为 'System.Collections.Generic.IEnumerable<SelectListItem>'

Cannot implicitly convert type 'System.Collections.Generic.List<InventoryLocations>' to 'System.Collections.Generic.IEnumerable<SelectListItem>'

asp.net-mvc

asp.net-core-mvc

viewmodel

selectlistitem