ios开发怎么获取输入的日期得到星期

+ (NSString*)weekdayStringFromDate:(NSDate*)inputDate {
    NSArray *weekdays = 
                      [NSArray arrayWithObjects: 
                      [NSNull null], @"Sunday", @"周一", @"周二", @"周三@"周四", @"周五", @"周六", nil];
     NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

   NSTimeZone *timeZone = [[NSTimeZone alloc] initWithName:@"Asia/Shanghai"];

   [calendar setTimeZone: timeZone];

   NSCalendarUnit calendarUnit = NSWeekdayCalendarUnit;

   NSDateComponents *theComponents = [calendar components:calendarUnit fromDate:inputDate];

   return [weekdays objectAtIndex:theComponents.weekday];

}