在多选列表框中显示选定的项目

Question

I have tried various ways to get this to work. I think maybe I have something missing in my model or controller, so I'm posting all three parts.

I have data in a database that shows some advising topics chosen by an advisor in a previous appointment. When the advisor calls up that appointment, the app should display a list of all possible topics with the ones previously chosen highlighted. Everything works except that last bit.

I know I'm retrieving the right information because I can display the selected items separately. I just can't get them to show up selected. Here's the code. I'm cutting out irrelevant parts.

public class AppointmentModel
{ ...
    public string AdvisingTopicId { get; set; }
    public List<SelectListItem> AdvisingIdList { get; set; }
    public SelectList AdvisingTopicNames { get; set; }
}

public class HomeController : AdvisorBaseController
{ ...
        var topicCodes = appointment.advising_topic.ToList();

        var advisingTopics = new SelectList((from t in topicCodes
                              select t.name).ToList(), "name");

        var topicsList = (from t in db.advising_topic
                          select new SelectListItem
                          {
                              Selected = false,
                              Text = t.name,
                              Value = SqlFunctions.StringConvert((double)t.advising_topic_id).Trim()
                          }).ToList();

        foreach (var topicCode in topicCodes)
        {
            var selTopic = topicsList.Find(x => x.Value == topicCode.advising_topic_id.ToString());
            if (selTopic != null)
            {
                selTopic.Selected = true;
            }
        } ...
            var appointmentModel = new AppointmentModel
            { ...
                AdvisingTopicNames = advisingTopics,
                AdvisingIdList = topicsList,
            };

and then the view

@model AcademicAdvising.Models.AppointmentModel
<h3>Advising Topics</h3>
<ul>
    @foreach (var item in Model.AdvisingTopicNames)
    {
        <li>@Html.DisplayFor(x => item)</li>
    }
</ul>
    @Html.ListBoxFor(m=>m.AdvisingIdList, new SelectList(Model.AdvisingTopicNames, "Value", "Text", Model.AdvisingTopicNames.SelectedValue))

Note that the foreach correctly displays the selected items. That's just for testing and will be pulled out. the ListBoxFor is where I'm struggling. What I have here doesn't work (shows the full list with nothing highlighted). And that's the bit where I have tried various approaches, with all fails.

Answer 1

It looks like you may have accidentely went a level too deep. You already have a select list which is all the listboxfor function wants.

 @Html.ListBoxFor(m=>m.AdvisingIdList, Model.AdvisingTopicNames)

But honestly looking at how you are defining your lists I think what you really want might be

 @Html.ListBoxFor(m=>m.AdvisingIdList, Model.AdvisingIdList)