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];

}