iOS NSDate 常用日期相关函数的封装

Category是类别，一般情况用分类好，用Category去重写类的方法，仅对本Category有效，不会影响到其他类与原有类的关系。

NSDate+Category.h 代码：

#import <Foundation/Foundation.h>

#define D_MINUTE      60
#define D_HOUR        3600
#define D_DAY         86400
#define D_WEEK        604800
#define D_YEAR        31556926

@interface NSDate (Category)

- (NSString *)timeIntervalDescription;　　　　//距离当前的时间间隔描述
- (NSString *)minuteDescription;　　　　　　　 //精确到分钟的日期描述*/
- (NSString *)formattedTime;
- (NSString *)formattedDateDescription;      //格式化日期描述
- (double)timeIntervalSince1970InMilliSecond;
+ (NSDate *)dateWithTimeIntervalInMilliSecondSince1970:(double)timeIntervalInMilliSecond;
+ (NSString *)formattedTimeFromTimeInterval:(long long)time;

//从当前日期起的相对日期
+ (NSDate *) dateTomorrow;
+ (NSDate *) dateYesterday;
+ (NSDate *) dateWithDaysFromNow: (NSInteger) days;
+ (NSDate *) dateWithDaysBeforeNow: (NSInteger) days;
+ (NSDate *) dateWithHoursFromNow: (NSInteger) dHours;
+ (NSDate *) dateWithHoursBeforeNow: (NSInteger) dHours;
+ (NSDate *) dateWithMinutesFromNow: (NSInteger) dMinutes;
+ (NSDate *) dateWithMinutesBeforeNow: (NSInteger) dMinutes;
+ (NSString *)weekdayStringValue:(NSDate*)date;

//日期比较
- (BOOL) isEqualToDateIgnoringTime: (NSDate *) aDate;
- (BOOL) isToday;
- (BOOL) isTomorrow;
- (BOOL) isYesterday;
- (BOOL) isSameWeekAsDate: (NSDate *) aDate;
- (BOOL) isThisWeek;
- (BOOL) isNextWeek;
- (BOOL) isLastWeek;
- (BOOL) isSameMonthAsDate: (NSDate *) aDate;
- (BOOL) isThisMonth;
- (BOOL) isSameYearAsDate: (NSDate *) aDate;
- (BOOL) isThisYear;
- (BOOL) isNextYear;
- (BOOL) isLastYear;
- (BOOL) isEarlierThanDate: (NSDate *) aDate;
- (BOOL) isLaterThanDate: (NSDate *) aDate;
- (BOOL) isInFuture;
- (BOOL) isInPast;

//工作日和休息日
- (BOOL) isTypicallyWorkday;
- (BOOL) isTypicallyWeekend;

//日期调整
- (NSDate *) dateByAddingDays: (NSInteger) dDays;
- (NSDate *) dateBySubtractingDays: (NSInteger) dDays;
- (NSDate *) dateByAddingHours: (NSInteger) dHours;
- (NSDate *) dateBySubtractingHours: (NSInteger) dHours;
- (NSDate *) dateByAddingMinutes: (NSInteger) dMinutes;
- (NSDate *) dateBySubtractingMinutes: (NSInteger) dMinutes;
- (NSDate *) dateAtStartOfDay;

//检索的时间间隔
- (NSInteger) minutesAfterDate: (NSDate *) aDate;
- (NSInteger) minutesBeforeDate: (NSDate *) aDate;
- (NSInteger) hoursAfterDate: (NSDate *) aDate;
- (NSInteger) hoursBeforeDate: (NSDate *) aDate;
- (NSInteger) daysAfterDate: (NSDate *) aDate;
- (NSInteger) daysBeforeDate: (NSDate *) aDate;
- (NSInteger)distanceInDaysToDate:(NSDate *)anotherDate;

//分解的日期
@property (readonly) NSInteger nearestHour;
@property (readonly) NSInteger hour;
@property (readonly) NSInteger minute;
@property (readonly) NSInteger seconds;
@property (readonly) NSInteger day;
@property (readonly) NSInteger month;
@property (readonly) NSInteger week;
@property (readonly) NSInteger weekday;
@property (readonly) NSInteger nthWeekday; // e.g. 2nd Tuesday of the month == 2
@property (readonly) NSInteger year;


#pragma mark 日期格式化
+ (id)dateFormatter;

+ (id)dateFormatterWithFormat:(NSString *)dateFormat;

+ (id)defaultDateFormatter;/*yyyy-MM-dd HH:mm:ss*/

@end

NSDate+Category.m 代码：

#import "NSDate+Category.h"

#define DATE_COMPONENTS (NSCalendarUnitYear| NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitWeekOfYear |  NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond | NSCalendarUnitWeekday | NSCalendarUnitWeekdayOrdinal)
#define CURRENT_CALENDAR [NSCalendar currentCalendar]

@implementation NSDate (Category)

/**
 *    @brief  距离当前的时间间隔描述
 *
 *    @param  paramete  请求参数
 *
 *    @return NSString格式的请求参数
 */
- (NSString *)timeIntervalDescription
{
    NSTimeInterval timeInterval = -[self timeIntervalSinceNow];
    if (timeInterval < 60) {
        return @"1分钟内";
    } else if (timeInterval < 3600) {
        return [NSString stringWithFormat:@"%ld分钟前", (long)timeInterval/60];
    } else if (timeInterval < 86400) {
        return [NSString stringWithFormat:@"%ld小时前", (long)timeInterval / 3600];
    } else if (timeInterval < 2592000) {//30天内
        return [NSString stringWithFormat:@"%ld天前", (long)timeInterval / 86400];
    } else if (timeInterval < 31536000) {//30天至1年内
        NSDateFormatter *dateFormatter = [NSDate dateFormatterWithFormat:@"M月d日"];
        return [dateFormatter stringFromDate:self];
    } else {
        return [NSString stringWithFormat:@"%ld年前", (long)timeInterval / 31536000];
    }
}

/**
 *    @brief  精确到分钟的日期描述
 *
 *    @param  paramete  请求参数
 *
 *    @return NSString格式的请求参数
 */
- (NSString *)minuteDescription
{
    NSDateFormatter *dateFormatter = [NSDate dateFormatterWithFormat:@"yyyy-MM-dd"];
    
    NSString *theDay = [dateFormatter stringFromDate:self];//日期的年月日
    NSString *currentDay = [dateFormatter stringFromDate:[NSDate date]];//当前年月日
    if ([theDay isEqualToString:currentDay]) {//当天
        [dateFormatter setDateFormat:@"ah:mm"];
        return [dateFormatter stringFromDate:self];
    } else if ([[dateFormatter dateFromString:currentDay] timeIntervalSinceDate:[dateFormatter dateFromString:theDay]] == 86400) {//昨天
        [dateFormatter setDateFormat:@"ah:mm"];
        return [NSString stringWithFormat:@"昨天 %@", [dateFormatter stringFromDate:self]];
    } else if ([[dateFormatter dateFromString:currentDay] timeIntervalSinceDate:[dateFormatter dateFromString:theDay]] < 86400 * 7) {//间隔一周内
        [dateFormatter setDateFormat:@"EEEE ah:mm"];
        return [dateFormatter stringFromDate:self];
    } else {//以前
        [dateFormatter setDateFormat:@"yyyy-MM-dd ah:mm"];
        return [dateFormatter stringFromDate:self];
    }
}

/**
 *    @brief  标准时间日期描述
 *
 *    @param  paramete  请求参数
 *
 *    @return NSString格式的请求参数
 */
-(NSString *)formattedTime{
    NSDateFormatter* formatter = [[NSDateFormatter alloc]init];
    [formatter setDateFormat:@"YYYY-MM-dd"];
    NSString * dateNow = [formatter stringFromDate:[NSDate date]];
    NSDateComponents *components = [[NSDateComponents alloc] init];
    [components setDay:[[dateNow substringWithRange:NSMakeRange(8,2)] intValue]];
    [components setMonth:[[dateNow substringWithRange:NSMakeRange(5,2)] intValue]];
    [components setYear:[[dateNow substringWithRange:NSMakeRange(0,4)] intValue]];
    NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    NSDate *date = [gregorian dateFromComponents:components]; //今天 0点时间
 
    NSInteger hour = [self hoursAfterDate:date];
    NSDateFormatter *dateFormatter = nil;
    NSString *ret = @"";
    
    //hasAMPM==TURE为12小时制，否则为24小时制
    NSString *formatStringForHours = [NSDateFormatter dateFormatFromTemplate:@"j" options:0 locale:[NSLocale currentLocale]];
    NSRange containsA = [formatStringForHours rangeOfString:@"a"];
    BOOL hasAMPM = containsA.location != NSNotFound;
    
    if (!hasAMPM) { //24小时制
        if (hour <= 24 && hour >= 0) {
            dateFormatter = [NSDate dateFormatterWithFormat:@"HH:mm"];
        }else if (hour < 0 && hour >= -24) {
            dateFormatter = [NSDate dateFormatterWithFormat:@"昨天HH:mm"];
        }else {
            dateFormatter = [NSDate dateFormatterWithFormat:@"yyyy-MM-dd HH:mm"];
        }
    }else {
        if (hour >= 0 && hour <= 6) {
            dateFormatter = [NSDate dateFormatterWithFormat:@"凌晨hh:mm"];
        }else if (hour > 6 && hour <=11 ) {
            dateFormatter = [NSDate dateFormatterWithFormat:@"上午hh:mm"];
        }else if (hour > 11 && hour <= 17) {
            dateFormatter = [NSDate dateFormatterWithFormat:@"下午hh:mm"];
        }else if (hour > 17 && hour <= 24) {
            dateFormatter = [NSDate dateFormatterWithFormat:@"晚上hh:mm"];
        }else if (hour < 0 && hour >= -24){
            dateFormatter = [NSDate dateFormatterWithFormat:@"昨天HH:mm"];
        }else  {
            dateFormatter = [NSDate dateFormatterWithFormat:@"yyyy-MM-dd HH:mm"];
        }
    }
    
    ret = [dateFormatter stringFromDate:self];
    return ret;
}


/**
 *    @brief  格式化日期描述
 *
 *    @param  paramete     请求参数
 *
 *    @return NSString格式的请求参数
 */
- (NSString *)formattedDateDescription
{
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    
    [dateFormatter setDateFormat:@"yyyy-MM-dd"];
    NSString *theDay = [dateFormatter stringFromDate:self];//日期的年月日
    NSString *currentDay = [dateFormatter stringFromDate:[NSDate date]];//当前年月日
    
    NSInteger timeInterval = -[self timeIntervalSinceNow];
    
    if (timeInterval < 60) {
        return @"1分钟内";
    } else if (timeInterval < 3600) {//1小时内
        return [NSString stringWithFormat:@"%ld分钟前", (long)timeInterval / 60];
    } else if (timeInterval < 21600) {//6小时内
        return [NSString stringWithFormat:@"%ld小时前", (long)timeInterval / 3600];
    } else if ([theDay isEqualToString:currentDay]) {//当天
        [dateFormatter setDateFormat:@"HH:mm"];
        return [NSString stringWithFormat:@"今天 %@", [dateFormatter stringFromDate:self]];
    } else if ([[dateFormatter dateFromString:currentDay] timeIntervalSinceDate:[dateFormatter dateFromString:theDay]] == 86400) {//昨天
        [dateFormatter setDateFormat:@"HH:mm"];
        return [NSString stringWithFormat:@"昨天 %@", [dateFormatter stringFromDate:self]];
    } else {//以前
        [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm"];
        return [dateFormatter stringFromDate:self];
    }
}

- (double)timeIntervalSince1970InMilliSecond {
    double ret;
    ret = [self timeIntervalSince1970] * 1000;
    
    return ret;
}

+ (NSDate *)dateWithTimeIntervalInMilliSecondSince1970:(double)timeIntervalInMilliSecond {
    NSDate *ret = nil;
    double timeInterval = timeIntervalInMilliSecond;
    // 判断参数是否在secconds中(对于以前的数据结构)
    if(timeIntervalInMilliSecond > 140000000000) {
        timeInterval = timeIntervalInMilliSecond / 1000;
    }
    ret = [NSDate dateWithTimeIntervalSince1970:timeInterval];
    
    return ret;
}

+ (NSString *)formattedTimeFromTimeInterval:(long long)time{
    return [[NSDate dateWithTimeIntervalInMilliSecondSince1970:time] formattedTime];
}

#pragma mark Relative Dates

+ (NSDate *) dateWithDaysFromNow: (NSInteger) days
{
    return [[NSDate date] dateByAddingDays:days];
}

+ (NSDate *) dateWithDaysBeforeNow: (NSInteger) days
{
    // Thanks, Jim Morrison
    return [[NSDate date] dateBySubtractingDays:days];
}

+ (NSDate *) dateTomorrow
{
    return [NSDate dateWithDaysFromNow:1];
}

+ (NSDate *) dateYesterday
{
    return [NSDate dateWithDaysBeforeNow:1];
}

+ (NSDate *) dateWithHoursFromNow: (NSInteger) dHours
{
    NSTimeInterval aTimeInterval = [[NSDate date] timeIntervalSinceReferenceDate] + D_HOUR * dHours;
    NSDate *newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
    return newDate;
}

+ (NSDate *) dateWithHoursBeforeNow: (NSInteger) dHours
{
    NSTimeInterval aTimeInterval = [[NSDate date] timeIntervalSinceReferenceDate] - D_HOUR * dHours;
    NSDate *newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
    return newDate;
}

+ (NSDate *) dateWithMinutesFromNow: (NSInteger) dMinutes
{
    NSTimeInterval aTimeInterval = [[NSDate date] timeIntervalSinceReferenceDate] + D_MINUTE * dMinutes;
    NSDate *newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
    return newDate;
}

+ (NSDate *) dateWithMinutesBeforeNow: (NSInteger) dMinutes
{
    NSTimeInterval aTimeInterval = [[NSDate date] timeIntervalSinceReferenceDate] - D_MINUTE * dMinutes;
    NSDate *newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
    return newDate;
}

+ (NSString *)weekdayStringValue:(NSDate*)date
{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSInteger unitFlags = NSWeekCalendarUnit|NSWeekdayCalendarUnit;
    NSDateComponents *comps = [calendar components:unitFlags fromDate:date];
    NSInteger weekday = [comps weekday];
    switch (weekday)
    {
        case 1:
            return @"星期天";
            break;
        case 2:
            return @"星期一";
            break;
        case 3:
            return @"星期二";
            break;
        case 4:
            return @"星期三";
            break;
        case 5:
            return @"星期四";
            break;
        case 6:
            return @"星期五";
            break;
        case 7:
            return @"星期六";
            break;
            
        default:
            break;
    }
    return nil;
}

#pragma mark Comparing Dates
- (BOOL) isEqualToDateIgnoringTime: (NSDate *) aDate
{
    NSDateComponents *components1 = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    NSDateComponents *components2 = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:aDate];
    return ((components1.year == components2.year) &&
            (components1.month == components2.month) &&
            (components1.day == components2.day));
}

- (BOOL) isToday
{
    return [self isEqualToDateIgnoringTime:[NSDate date]];
}

- (BOOL) isTomorrow
{
    return [self isEqualToDateIgnoringTime:[NSDate dateTomorrow]];
}

- (BOOL) isYesterday
{
    return [self isEqualToDateIgnoringTime:[NSDate dateYesterday]];
}

- (BOOL) isSameWeekAsDate: (NSDate *) aDate
{
    NSDateComponents *components1 = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    NSDateComponents *components2 = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:aDate];
    
    // 必须在同一周。12/31和1/1如果在同一周，都是周1
    if (components1.weekOfYear != components2.weekOfYear) return NO;
    
    // 必须有一个时间间隔不到1周
    return (fabs([self timeIntervalSinceDate:aDate]) < D_WEEK);
}

- (BOOL) isThisWeek
{
    return [self isSameWeekAsDate:[NSDate date]];
}

- (BOOL) isNextWeek
{
    NSTimeInterval aTimeInterval = [[NSDate date] timeIntervalSinceReferenceDate] + D_WEEK;
    NSDate *newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
    return [self isSameWeekAsDate:newDate];
}

- (BOOL) isLastWeek
{
    NSTimeInterval aTimeInterval = [[NSDate date] timeIntervalSinceReferenceDate] - D_WEEK;
    NSDate *newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
    return [self isSameWeekAsDate:newDate];
}

- (BOOL) isSameMonthAsDate: (NSDate *) aDate
{
    NSDateComponents *components1 = [CURRENT_CALENDAR components:NSCalendarUnitYear | NSCalendarUnitMonth fromDate:self];
    NSDateComponents *components2 = [CURRENT_CALENDAR components:NSCalendarUnitYear | NSCalendarUnitMonth fromDate:aDate];
    return ((components1.month == components2.month) &&
            (components1.year == components2.year));
}

- (BOOL) isThisMonth
{
    return [self isSameMonthAsDate:[NSDate date]];
}

- (BOOL) isSameYearAsDate: (NSDate *) aDate
{
    NSDateComponents *components1 = [CURRENT_CALENDAR components:NSCalendarUnitYear fromDate:self];
    NSDateComponents *components2 = [CURRENT_CALENDAR components:NSCalendarUnitYear fromDate:aDate];
    return (components1.year == components2.year);
}

- (BOOL) isThisYear
{
    return [self isSameYearAsDate:[NSDate date]];
}

- (BOOL) isNextYear
{
    NSDateComponents *components1 = [CURRENT_CALENDAR components:NSCalendarUnitYear fromDate:self];
    NSDateComponents *components2 = [CURRENT_CALENDAR components:NSCalendarUnitYear fromDate:[NSDate date]];
    
    return (components1.year == (components2.year + 1));
}

- (BOOL) isLastYear
{
    NSDateComponents *components1 = [CURRENT_CALENDAR components:NSCalendarUnitYear fromDate:self];
    NSDateComponents *components2 = [CURRENT_CALENDAR components:NSCalendarUnitYear fromDate:[NSDate date]];
    
    return (components1.year == (components2.year - 1));
}

- (BOOL) isEarlierThanDate: (NSDate *) aDate
{
    return ([self compare:aDate] == NSOrderedAscending);
}

- (BOOL) isLaterThanDate: (NSDate *) aDate
{
    return ([self compare:aDate] == NSOrderedDescending);
}

- (BOOL) isInFuture
{
    return ([self isLaterThanDate:[NSDate date]]);
}

- (BOOL) isInPast
{
    return ([self isEarlierThanDate:[NSDate date]]);
}

#pragma mark Roles
- (BOOL) isTypicallyWeekend
{
    NSDateComponents *components = [CURRENT_CALENDAR components:NSCalendarUnitWeekday fromDate:self];
    if ((components.weekday == 1) ||
        (components.weekday == 7))
        return YES;
    return NO;
}

- (BOOL) isTypicallyWorkday
{
    return ![self isTypicallyWeekend];
}

#pragma mark Adjusting Dates

- (NSDate *) dateByAddingDays: (NSInteger) dDays
{
    NSTimeInterval aTimeInterval = [self timeIntervalSinceReferenceDate] + D_DAY * dDays;
    NSDate *newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
    return newDate;
}

- (NSDate *) dateBySubtractingDays: (NSInteger) dDays
{
    return [self dateByAddingDays: (dDays * -1)];
}

- (NSDate *) dateByAddingHours: (NSInteger) dHours
{
    NSTimeInterval aTimeInterval = [self timeIntervalSinceReferenceDate] + D_HOUR * dHours;
    NSDate *newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
    return newDate;
}

- (NSDate *) dateBySubtractingHours: (NSInteger) dHours
{
    return [self dateByAddingHours: (dHours * -1)];
}

- (NSDate *) dateByAddingMinutes: (NSInteger) dMinutes
{
    NSTimeInterval aTimeInterval = [self timeIntervalSinceReferenceDate] + D_MINUTE * dMinutes;
    NSDate *newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
    return newDate;
}

- (NSDate *) dateBySubtractingMinutes: (NSInteger) dMinutes
{
    return [self dateByAddingMinutes: (dMinutes * -1)];
}

- (NSDate *) dateAtStartOfDay
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    components.hour = 0;
    components.minute = 0;
    components.second = 0;
    return [CURRENT_CALENDAR dateFromComponents:components];
}

- (NSDateComponents *) componentsWithOffsetFromDate: (NSDate *) aDate
{
    NSDateComponents *dTime = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:aDate toDate:self options:0];
    return dTime;
}

#pragma mark Retrieving Intervals

- (NSInteger) minutesAfterDate: (NSDate *) aDate
{
    NSTimeInterval ti = [self timeIntervalSinceDate:aDate];
    return (NSInteger) (ti / D_MINUTE);
}

- (NSInteger) minutesBeforeDate: (NSDate *) aDate
{
    NSTimeInterval ti = [aDate timeIntervalSinceDate:self];
    return (NSInteger) (ti / D_MINUTE);
}

- (NSInteger) hoursAfterDate: (NSDate *) aDate
{
    NSTimeInterval ti = [self timeIntervalSinceDate:aDate];
    return (NSInteger) (ti / D_HOUR);
}

- (NSInteger) hoursBeforeDate: (NSDate *) aDate
{
    NSTimeInterval ti = [aDate timeIntervalSinceDate:self];
    return (NSInteger) (ti / D_HOUR);
}

- (NSInteger) daysAfterDate: (NSDate *) aDate
{
    NSTimeInterval ti = [self timeIntervalSinceDate:aDate];
    return (NSInteger) (ti / D_DAY);
}

- (NSInteger) daysBeforeDate: (NSDate *) aDate
{
    NSTimeInterval ti = [aDate timeIntervalSinceDate:self];
    return (NSInteger) (ti / D_DAY);
}

- (NSInteger)distanceInDaysToDate:(NSDate *)anotherDate
{
    NSCalendar *gregorianCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    NSDateComponents *components = [gregorianCalendar components:NSCalendarUnitDay fromDate:self toDate:anotherDate options:0];
    return components.day;
}

#pragma mark Decomposing Dates

- (NSInteger) nearestHour
{
    NSTimeInterval aTimeInterval = [[NSDate date] timeIntervalSinceReferenceDate] + D_MINUTE * 30;
    NSDate *newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
    NSDateComponents *components = [CURRENT_CALENDAR components:NSCalendarUnitHour fromDate:newDate];
    return components.hour;
}

- (NSInteger) hour
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.hour;
}

- (NSInteger) minute
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.minute;
}

- (NSInteger) seconds
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.second;
}

- (NSInteger) day
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.day;
}

- (NSInteger) month
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.month;
}

- (NSInteger) week
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.weekOfYear;
}

- (NSInteger) weekday
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.weekday;
}

- (NSInteger) nthWeekday // e.g. 2nd Tuesday of the month is 2
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.weekdayOrdinal;
}

- (NSInteger) year
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.year;
}

#pragma mark 格式化日期
+ (id)dateFormatter
{
    return [[self alloc] init];
}

+ (id)dateFormatterWithFormat:(NSString *)dateFormat
{
    NSDateFormatter *dateFormatter = [[self alloc] init];
    dateFormatter.dateFormat = dateFormat;
    return dateFormatter;
}

+ (id)defaultDateFormatter
{
    return [self dateFormatterWithFormat:@"yyyy-MM-dd HH:mm:ss"];
}

@end