判斷是否為今年

• 取出日期的年份進行比較，如果一樣返回1，不一樣就返回0。

- (BOOL) isThisYear{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    
    NSInteger *nowYear = (NSInteger *)[calendar component:NSCalendarUnitYear fromDate:[NSDate date]];
    NSInteger *selfYear = (NSInteger *)[calendar component:NSCalendarUnitYear fromDate:self];
    return  nowYear == selfYear;
    
}

判斷是否為今天

• 取出當前日期和要比較日期的年月日，并將它們的類型從Date類型轉成NSString類型，然后判斷2者是否相等，相等返回1，不相等返回0。

- (BOOL) isToday{
    NSDateFormatter *fmt = [[NSDateFormatter alloc]init];
    fmt.dateFormat = @"yyyy-mm-dd";
    
    NSString *nowDay = [fmt stringFromDate:[NSDate date]];
    NSString *selfDay = [fmt stringFromDate:self];
    
    return [nowDay isEqualToString:selfDay];

}

判斷是否為昨天

• 取出當前日期和要比較日期的年月日，并將它們的類型從Date類型轉成NSString類型，然后再將NSString類型轉回Data類型，然后用[calendar components:NSCalendarUnitDay fromDate:selfDate toDate:nowDate options:0]來比較要比較的日期和當前日期相差多少天，如果components.year == 0 && components.month == 0 && components.day == 1;
  則返回 1，否則返回0。

- (BOOL) isYesterday{
    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 *components = [calendar components:NSCalendarUnitDay fromDate:selfDate toDate:nowDate options:0];
    return components.year == 0
    && components.month == 0
    && components.day == 1;
    

}