根据NSdate 计算出星期

-(NSString*)weekdayStringFromDate:(NSDate*)inputDate {
    
    NSArray *weekdays = [NSArray arrayWithObjects: [NSNull null], @"星期天", @"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];
    
}