MVC 3:如何在选择下拉列表项时更新复选框列表

在过去的两天里，我试图弄清楚当在 JavaScript 的帮助下选择下拉列表中的新项目时如何动态更新复选框列表。

一周前我做了同样的事情，我应该从下拉列表更新到下拉列表。

到目前为止，我得到了什么：

视图

@using (Html.BeginForm())
{
    @Html.DropDownListFor(x => x.User, (IEnumerable<SelectListItem>)Model.UserList, "-- vælg bruger --")
    if (Model.checkboxlist != null)
    {
       for (var i = 0; i < Model.checkboxlist.Count; i++)
       {
        <div class="editor-label">
           @Html.CheckBoxFor(c => Model.checkboxlist[i].check)
            @Html.LabelFor(c => Model.checkboxlist[i].Id, Model.checkboxlist[i].Id)
            @Html.HiddenFor(c => Model.checkboxlist[i].Id)
        </div>
       }
    }
}
<script type="text/javascript">
    $('#User').change(function () {
    alert('HEJ!');
        var selectedUser = $(this).val();
        alert(selectedUser);
        if (selectedUser != null && selectedUser != '-- vælg bruger --' && selectedUser != '') {
            $.getJSON('@Url.Action("getPdfCheckBoxList","Admin")', { username: selectedUser },
            function (employee) {
                var checkboxlist = $('#checkboxlist');
                checkboxlist.empty();
                $.each(employee, function (index, employee) {
                    checkboxlist.append($('<checkbox/>', {
                        checked = 'false'
                    }));
                });
            });
        }
    });
</script>

当我加载视图模型时，复选框列表为空，因为我不会返回任何内容来建模下拉列表项。

控制器操作 ：

public ActionResult getPdfCheckBoxList(String username)
{
    MethodService service = new MethodService();
    var list = new List<PDFCheckBoxList>();

    foreach (var pdfCheckBoxList in getPDFFileNames(username))
    {
        list.Add(new PDFCheckBoxList { check = false, Id = pdfCheckBoxList });
    }
    return Json(list, JsonRequestBehavior.AllowGet);
} 

现在连警报（"HEJ"）都没有被解雇，我根本想不通为什么......请帮忙？

@using (Html.BeginForm())
{
    @Html.DropDownListFor(
        x => x.User, 
        Model.UserList, 
        "-- vælg bruger --",
        data_url = Url.Action("getPdfCheckBoxList", "Admin")
    )
    <div id="checkboxlist">
        @if (Model.checkboxlist != null)
        {
            @Html.Partial("_checkboxlist", Model.checkboxlist)
        }
    </div>
}

@model IEnumerable<PDFCheckBoxList>
@{
    ViewData.TemplateInfo.HtmlFieldPrefix = "checkboxlist";
}
@Html.EditorForModel()

@model PDFCheckBoxList
<div class="editor-label">
    @Html.CheckBoxFor(c => c.check)
    @Html.LabelFor(c => c.Id, Model.Id)
    @Html.HiddenFor(c => c.Id)
</div>

<script type="text/javascript">
    // Now that we no longer have any server side 
    // code here we could externalize this script
    // into a separate javascript file
    $('#User').change(function () {
        if (selectedUser != null && selectedUser != '') {
            var selectedUser = $(this).val();
            var url = $(this).data('url');
            var data = { username: selectedUser };
            $('#checkboxlist').load(url, data);
        }
    });
</script>

public ActionResult getPdfCheckBoxList(String username)
{
    var service = new MethodService();
    var list = getPDFFileNames(username)
        .Select(x => new PDFCheckBoxList 
        { 
            check = false, 
            Id = x 
        })
        .ToList();
    return PartialView("_checkboxlist", list);
}