UIDatePicker *pick = [[UIDatePicker alloc] init];

pick.datePickerMode = UIDatePickerModeTime;

    UIDatePickerModeTime,           // Displays hour, minute, and optionally AM/PM designation depending on the locale setting (e.g. 6 | 53 | PM)
    UIDatePickerModeDate,           // Displays month, day, and year depending on the locale setting (e.g. November | 15 | 2007)
    UIDatePickerModeDateAndTime,    // Displays date, hour, minute, and optionally AM/PM designation depending on the locale setting (e.g. Wed Nov 15 | 6 | 53 | PM)
    UIDatePickerModeCountDownTimer, // Displays hour and minute (e.g. 1 | 53)

[pick addTarget:self action:@selector(setTimeOK:) forControlEvents:UIControlEventValueChanged];

- (void)setTimeOK:(UIDatePicker *)sender{
    NSDate *date = sender.date;
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    formatter.dateFormat = @"yyyy-MM-dd HH:mm:ss"; 
    NSString *dateStr = [formatter stringFromDate:date];
    self.textField.text = [NSString stringWithFormat:@"%@", dateStr];
 }

typedef enum {
    NSDateFormatterNoStyle     = kCFDateFormatterNoStyle,
    NSDateFormatterShortStyle  = kCFDateFormatterShortStyle,//“11/23/37” or “3:30pm”
    NSDateFormatterMediumStyle = kCFDateFormatterMediumStyle,//\"Nov 23, 1937\"
    NSDateFormatterLongStyle   = kCFDateFormatterLongStyle,//\"November 23, 1937” or “3:30:32pm\"
    NSDateFormatterFullStyle   = kCFDateFormatterFullStyle//“Tuesday, April 12, 1952 AD” or “3:30:42pm PST”
} NSDateFormatterStyle;