+ (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];
}