ASP.NET MVC MultiSelectList 选中项不起作用

Question

I trying to use the MultiSelectList in ASP.NET MVC with selected items.

This is the backend code:

var listPoles = new List<long>();

foreach (var pole in employeePole.PolesList)
                listPoles.Add(pole.Id);

            ViewBag.poles = new MultiSelectList(GetPoles(), "Id", "Name", listPoles);

GetPoles() returns IReadOnlyList .

HTML code (view):

<select multiple="multiple" title="selecione..." class="form-control selectpicker" id="poles" asp-for="@Model.Poles" asp-items="@ViewBag.poles"></select>

In edit view (front-end) the select component does not load the selected items but I used the exactly same code (with different entity) in another CRUD in the same system and it works fine.

I tried to use a lot of different types of collection (enumerable, readonlylist, list, etc) to create the selected items list but nothing works

What can possibly be wrong?

Answer 1

1. Try to debug if the list is filled with data.
2. Don't invoke GetPoles() method into MultiSelectList constructor, use a variable for this for clean code reasons
3. Check if GetPoles() does not contain asynchronous method
4. Viewbag can be cleaned after read. Try to use the model instead.