func datePickerValueChanged(sender: UIDatePicker) {

    let dateFormatter = NSDateFormatter()

    dateFormatter.dateStyle = NSDateFormatterStyle.MediumStyle

    dateFormatter.timeStyle = NSDateFormatterStyle.NoStyle
    dateFormatter.dateFormat = NSCalendarIdentifierPersian

    dateOutlet.text = dateFormatter.stringFromDate(sender.date)

}

我将日期格式更改为NSCalendarIdentifierPersian但是datepicker没有任何变化？