call_user_func() in yii2

i can’t debug the following error, someone please help me

call_user_func() expects parameter 1 to be a valid callback, class ‘app\modules\WebForm\components\helpers\ElementHelper’ does not have a method ‘$display_func@web/assets’

[code]$element_markup = call_user_func(‘app\modules\WebForm\components\helpers\ElementHelper::$display_func’. $images_url, $webform_lang, $element_properties_obj, “Edit”,true );[code]