a ModelAdmin with sortable gridfield (if the managed model has a field "SortOrder")

MySortableAdmin.php

<?php

class MySortableAdmin extends ModelAdmin
{
    private static $managed_models = [
        'MySortableDataObject'
    ];

    private static $url_segment = "sorable-demo";
    private static $menu_title = "Sort stuff";
    public $showImportForm = false;

    public function getEditForm($id = null, $fields = null) {
        $form=parent::getEditForm($id, $fields);

        $model = singleton($this->modelClass);

        /** add sorting if we have a field for... */
        if (class_exists('GridFieldSortableRows')
            && $model->hasField('SortOrder')
            && $gridField=$form->Fields()->dataFieldByName($this->sanitiseClassName($this->modelClass))) {
            if($gridField instanceof GridField) {
                $gridField->getConfig()->addComponent(new GridFieldSortableRows('SortOrder'));
            }
        }

        return $form;
    }
}