Question

for last two days i was trying to figure out how to update a checkboxlist dynamicly when a new item in dropdownlist is selected by help of javascript.

Ive done same thing for a week ago where i should do update to a from a dropdownlist to a dropdownlist.

What ive got so far :

View

@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>

when i am loading view Model.checkboxlist is null cause i dont return anything to model apart of dropdownlist items.

ControllerAction :

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);
} 

Right now even Alert(“HEJ”) doesnt even get fired, and i simply cant figure out why… Help please?

Answer 1

You could use partial views and have your controller action return a partial and build the markup on the server instead of doing it on the client:

@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>
}

and then define _checkboxlist.cshtml:

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

and finally the editor template ~/Views/Shared/EditorTemplates/PDFCheckBoxList.cshtml which will be rendered for each element:

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

Now you could modify your javascript like so:

<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>

and finally your getPdfCheckBoxList action:

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);
}

If you want to build the markup on the client and have the controller action return JSON I would recommend you using some javascript templating framework.