asp.net - 未为 ASP.Net MVC 3 DropDownListFor 设置所选值

Question

我有一个父 View 模型绑定(bind)到一个 View ，该 View 包含一个属性，该属性是其他 View 模型的列表。

这是父 View 模型代码:

var timeAvailability = (from u in _entities.UserTimeAvailabilities
                                    where u.UserId == userId
                                    select u).ToList();
            for(int index = 0; index < timeAvailability.Count; index++)
            {
                var availableTime = timeAvailability[index];
                TimeAvailability.Add(new AvailableTimeSlotViewModel(index)
                                         {
                                             SelectedDay = availableTime.DayId,
                                             SelectedStartTime = availableTime.StartHourId.HasValue ? availableTime.StartHourId.Value : 0,
                                             SelectedEndTime = availableTime.EndHourId.HasValue ? availableTime.EndHourId.Value : 0
                                         });
            }

可用时间是一个列表

这是可用的TimeSlotViewModel:

public List<SelectListItem> Days { get; set; }
    public int Index { get; set; }
    public List<SelectListItem> Hours { get; set; }
    [Display(Name = "Select Day")]
    public int SelectedDay { get; set; }
    [Display(Name="Start Time")]
    public int SelectedStartTime { get; set; }
    [Display(Name = "End Time")]
    public int SelectedEndTime { get; set; }

    public AvailableTimeSlotViewModel(int index)
    {
        Index = index;
        _entities = Repository.GetRepository();
        Days = new List<SelectListItem>();
        _entities.Days.ToList().ForEach(d => Days.Add(new SelectListItem { Value = d.DayId.ToString(), Text = d.Name }));
        Hours = new List<SelectListItem>();
        _entities.Hours.ToList().ForEach(h => Hours.Add(new SelectListItem { Value = h.HourId.ToString(), Text = h.Name }));
    }

View 中绑定(bind)到 UserPreferences 的代码:

<div id="time-availability-div">                
            @for (int index = 0; index < Model.TimeAvailability.Count; index++)
            {                    
                <table>
                    <thead>
                        <tr>
                            <td>
                                @Html.LabelFor(m => m.TimeAvailability[index].SelectedDay)
                            </td>
                            <td>
                                @Html.LabelFor(m => m.TimeAvailability[index].SelectedStartTime)
                            </td>
                            <td>
                                @Html.LabelFor(m => m.TimeAvailability[index].SelectedEndTime)
                            </td>
                        </tr>
                    </thead>
                    <tbody>
                        <tr>
                            <td>
                                @Html.DropDownListFor(m => m.TimeAvailability[index].SelectedDay, Model.Days)
                            </td>
                            <td>
                                @Html.DropDownListFor(m => m.TimeAvailability[index].SelectedStartTime, Model.Hours)
                            </td>
                            <td>
                                @Html.DropDownListFor(m => m.TimeAvailability[index].SelectedEndTime, Model.Hours)
                            </td>
                        </tr>
                    </tbody>
                </table>                   
            }
        </div>

需要注意的一件事是，如果我在 DropDownListFor 中显式设置所选值，它就可以正常工作。我想知道为什么所选值没有自动绑定(bind)引用索引处的属性。

Answer 1

I'm wondering why the selected value isn't bound automatically referencing the property at index.

因为您使用了复杂的集合 lambda 表达式作为第一个参数:m => m.TimeAvailability[index].SelectedEndTime。不幸的是，DropDownListFor 帮助器不支持自动设置此类复杂表达式的默认值，您需要设置选定的值:

@Html.DropDownListFor(
    m => m.TimeAvailability[index].SelectedEndTime, 
    new SelectList(Model.Hours, "Value", "Text", Model.TimeAvailability[index].SelectedEndTime)
)