_list_toolbar.htm

<a
        class="btn btn-default oc-icon-sitemap"
        data-control="popup"
        data-handler="onShowReorderPopup"
        href="javascript:;"
    >
        Reorder Categories
    </a>

_reorder_form.htm

<?= Form::open(['id' => 'disableForm']) ?>
    <div class="modal-header">
        <button type="button" class="close" data-dismiss="popup">&times;</button>
        <h4 class="modal-title">Reorder Categories</h4>
    </div>
    <div class="modal-body">

        <?php if ($this->fatalError): ?>
        <p class="flash-message static error"><?= $fatalError ?></p>
        <?php endif ?>

        <div class="form">
            <?= $this->reorderRender() ?>
        </div>

    </div>

    <div class="modal-footer">
        <button
            type="submit"
            class="btn btn-primary"
            data-request="onRefreshList"
            data-dismiss="popup"
            data-stripe-load-indicator
        >
            Save
        </button>
        <button
                type="button"
                class="btn btn-default"
                data-dismiss="popup">
            Close
        </button>
    </div>
<?= Form::close() ?>

Controller.php

/**
     * Renders the reorder popup
     *
     * @param null $recordId
     * @return mixed
     * @throws \SystemException
     */
    public function index_onShowReorderPopup($recordId = null) {
        $this->reorder();
        return $this->makePartial('reorder_form');
    }