日期比较

- (NSDateComponents *)deltaFrom:(NSDate *)from{    // 日历    NSCalendar *calendar = [NSCalendar currentCalendar];    // 比较时间    NSCalendarUnit unit = NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;    return [calendar components:unit fromDate:from toDate:self options:0];}- (BOOL)isThisYear{    // 日历    NSCalendar *calendar = [NSCalendar currentCalendar];    NSInteger nowYear = [calendar component:NSCalendarUnitYear fromDate:[NSDate date]];    NSInteger selfYear = [calendar component:NSCalendarUnitYear fromDate:self];    return nowYear == selfYear;}//- (BOOL)isToday//{//    // 日历//    NSCalendar *calendar = [NSCalendar currentCalendar];//    //    NSCalendarUnit unit = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay;//    //    NSDateComponents *nowCmps = [calendar components:unit fromDate:[NSDate date]];//    NSDateComponents *selfCmps = [calendar components:unit fromDate:self];//    //    return nowCmps.year == selfCmps.year//    && nowCmps.month == selfCmps.month//    && nowCmps.day == selfCmps.day;//}- (BOOL)isToday{    NSDateFormatter *fmt = [[NSDateFormatter alloc] init];    fmt.dateFormat = @"yyyy-MM-dd";    NSString *nowString = [fmt stringFromDate:[NSDate date]];    NSString *selfString = [fmt stringFromDate:self];    return [nowString isEqualToString:selfString];}- (BOOL)isYesterday{    // 2014-12-31 23:59:59 -> 2014-12-31    // 2015-01-01 00:00:01 -> 2015-01-01    // 日期格式化类    NSDateFormatter *fmt = [[NSDateFormatter alloc] init];    fmt.dateFormat = @"yyyy-MM-dd";    NSDate *nowDate = [fmt dateFromString:[fmt stringFromDate:[NSDate date]]];    NSDate *selfDate = [fmt dateFromString:[fmt stringFromDate:self]];    NSCalendar *calendar = [NSCalendar currentCalendar];    NSDateComponents *cmps = [calendar components:NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear fromDate:selfDate toDate:nowDate options:0];    return cmps.year == 0    && cmps.month == 0    && cmps.day == 1;}