MVC的dropdownlistfor对于多选不起作用，只是打开完整的列表？

@Html.ListBoxFor(m => m.SelectedOptions, Model.Options)

<select multiple id="mySelect">
    <option value="option1">Option 1</option>
    <option value="option2">Option 2</option>
    <option value="option3">Option 3</option>
</select>

<script>
    // 获取选中的选项
    function getSelectedOptions() {
        var select = document.getElementById("mySelect");
        var selectedOptions = [];
        for (var i = 0; i < select.options.length; i++) {
            if (select.options[i].selected) {
                selectedOptions.push(select.options[i].value);
            }
        }
        return selectedOptions;
    }
</script>