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I am using a jquery multiselect plugin [https://github.com/davidstutz/bootstrap-multiselect] and binding it dynamically with database values.

HTML

@Html.ListBoxFor(m => m.Classes, new SelectList(Model.Classes, "Value", "Text"), new { @id = "classList" })

SCRIPT

$('#classList').multiselect({ enableClickableOptGroups: true });

The model in the view is a view model and contains a property for a SelectList

public class SearchControlViewModel 
{
    ....
    public SelectList Classes { get; set; }
}

and the code in the controller

SearchControlViewModel  model = new SearchControlViewModel()
{
    ....
    Classes = new SelectList(repClass.GetClassesByYear(23), "classID", "classname")
};
return View(model);

It works like a charm except for one thing - I want to add grouping/group header like <optgroup> does. How can I do that?

The GetClassesByYear() method used for generating the SelectList returns an object containing properties int classID, string classname and string grade and I want to be able to group the options by grade.

Samra
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  • Are you using MVC-5 (which supports option grouping for `SelectListItem`)? –  Mar 27 '17 at 00:34
  • MVC 4 unfortunately – Samra Mar 27 '17 at 00:34
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    Then your out of luck (unless you generate the html manually) - your will need to upgrade (for an example, refer [this answer](http://stackoverflow.com/questions/37151572/constructing-a-select-list-with-optgroup-groups)) –  Mar 27 '17 at 00:36
  • can i do something like parse the generated html and then add groupopts myself? any hints/examples? – Samra Mar 27 '17 at 00:40
  • I guess you could pass model to the view indicating the groups and which option belongs in each group, and then assign that to a javascript variable, and then use javascript to build the `` and ` –  Mar 27 '17 at 00:45
  • Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/139110/discussion-between-stephen-muecke-and-samra). –  Mar 27 '17 at 00:47

1 Answers1

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Option groups are not supported in MVC-4, and you would need to upgrade to MVC-5 to make use out-of-the-box functions. If you do upgrade, refer Constructing a Select List with OptGroup groups for examples using both the SelectList constructor, and by generating an IEnumerable<SelectListItem>

Without upgrading, you could pass a model representing your groups and their options to the view , and use some javascript/jquery to generate the elements. Start by creating some additional view models

public class OptionGroupVM
{
    public string GroupName { get; set; }
    public IEnumerable<OptionVM> Options { get; set; }
}
public class OptionVM
{
    public string Value { get; set; }
    public string Text { get; set; }
    public bool IsSelected { get; set; } // Only applicable if your not binding to a model property
}

Then modify your main view model to include the following

public class SearchControlViewModel 
{
    ....
    public IEnumerable<int> SelectedClasses { get; set; }
    public IEnumerable<OptionGroupVM> ClassOptions { get; set; }
}

Note that your current model and use of ListBoxFor() is incorrect because

  1. you cannot bind a <select multiple> to a collection of complex objects which your Classes property is - the model needs to be a collection of value types, and

  2. you cannot use the same name for the property your binding to and the SelectList - refer Will there be any conflict if i specify the viewBag name to be equal to the model property name inside @Html.DropDownListFor for more detail

In the controller

var data = repClass.GetClassesByYear(23);
var groupedOptions = data.GroupBy(x => x.grade).Select(x => new OptionGroupVM()
{
    GroupName = x.Key.ToString(),
    Options = x.Select(y => new OptionVM()
    {
        Value = y.classId.ToString(),
        Text = y.classcame,
    })
});
SearchControlViewModel model = new SearchControlViewModel()
{
    ....
    SelectedClasses = ...., // the values of the options that will be pre-selected
    ClassOptions = groupedOptions
};
return View(model);

And in the view use

@Html.ListBoxFor(m => SelectedClasses, Enumerable.Empty<SelectListItem>(), new { id = "classList" })

which will initially generate the <select> without any options. Then use the following script to generate the options

<script type="text/javascript">
    // Get data
    var listBox = $('#classList');
    var selected = @Html.Raw(Json.Encode(Model.SelectedClasses));
    var groups = @Html.Raw(Json.Encode(Model.ClassOptions));

    // Generate options
    createGroupedOptions(listBox, selected, groups);
    // Attach plug-in
    listBox.multiselect({ enableClickableOptGroups: true });

    // This function could be in an external js file
    function createGroupedOptions(element, selected, groups) {
        for (var i = 0; i < groups.length; i++) {
            var group = groups[i];
            var groupElement = $('<optgroup></optgroup>').attr('label', group.GroupName);
            for(var j = 0; j < group.Options.length; j++) {
                var option = group.Options[j];
                var optionElement = $('<option></option>').val(option.Value).text(option.Text);
                if (selected) {
                    if (selected.toString().indexOf(option.Value) >= 0) {
                        optionElement.attr('selected', 'selected')
                    }
                } else {
                    if (option.IsSelected) {
                        optionElement.attr('selected', 'selected')
                    }
                }

                $(groupElement).append(optionElement);
            }
            $(element).append(groupElement);
        }
    }
</script>
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