ios开发分类--NSDate+Helpers

#import <Foundation/Foundation.h>
@interface NSDate (Helpers) 
@end

#import "Date.h"

@implementation NSDate(Helpers)

//获取年月日如:19871127.
- (NSString *)getFormatYearMonthDay
{
    NSString *string = [NSString stringWithFormat:@"%d%02d%02d",[self getYear],[self getMonth],[self getDay]];
    return string;
}

//该日期是该年的第几周
- (int )getWeekOfYear
{
    int i;
    int year = [self getYear];
    NSDate *date = [self endOfWeek];
    for (i = 1;[[date dateAfterDay:-7 * i] getYear] == year;i++) 
    {
    }
    return i;
}
//返回day天后的日期(若day为负数,则为|day|天前的日期)
- (NSDate *)dateAfterDay:(int)day
{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    // Get the weekday component of the current date
    // NSDateComponents *weekdayComponents = [calendar components:NSWeekdayCalendarUnit fromDate:self];
    NSDateComponents *componentsToAdd = [[NSDateComponents alloc] init];
    // to get the end of week for a particular date, add (7 - weekday) days
    [componentsToAdd setDay:day];
    NSDate *dateAfterDay = [calendar dateByAddingComponents:componentsToAdd toDate:self options:0];
    [componentsToAdd release];
    
    return dateAfterDay;
}
//month个月后的日期
- (NSDate *)dateafterMonth:(int)month
{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *componentsToAdd = [[NSDateComponents alloc] init];
    [componentsToAdd setMonth:month];
    NSDate *dateAfterMonth = [calendar dateByAddingComponents:componentsToAdd toDate:self options:0];
    [componentsToAdd release];
    
    return dateAfterMonth;
}
//获取日
- (NSUInteger)getDay{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *dayComponents = [calendar components:(NSDayCalendarUnit) fromDate:self];
    return [dayComponents day];
}
//获取月
- (NSUInteger)getMonth
{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *dayComponents = [calendar components:(NSMonthCalendarUnit) fromDate:self];
    return [dayComponents month];
}
//获取年
- (NSUInteger)getYear
{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *dayComponents = [calendar components:(NSYearCalendarUnit) fromDate:self];
    return [dayComponents year];
}
//获取小时
- (int )getHour {
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSUInteger unitFlags =NSYearCalendarUnit| NSMonthCalendarUnit | NSDayCalendarUnit |NSHourCalendarUnit|NSMinuteCalendarUnit;
    NSDateComponents *components = [calendar components:unitFlags fromDate:self];
    NSInteger hour = [components hour];
    return (int)hour;
}
//获取分钟
- (int)getMinute {
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSUInteger unitFlags =NSYearCalendarUnit| NSMonthCalendarUnit | NSDayCalendarUnit |NSHourCalendarUnit|NSMinuteCalendarUnit;
    NSDateComponents *components = [calendar components:unitFlags fromDate:self];
    NSInteger minute = [components minute];
    return (int)minute;
}
- (int )getHour:(NSDate *)date {
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSUInteger unitFlags =NSYearCalendarUnit| NSMonthCalendarUnit | NSDayCalendarUnit |NSHourCalendarUnit|NSMinuteCalendarUnit;
    NSDateComponents *components = [calendar components:unitFlags fromDate:date];
    NSInteger hour = [components hour];
    return (int)hour;
}
- (int)getMinute:(NSDate *)date {
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSUInteger unitFlags =NSYearCalendarUnit| NSMonthCalendarUnit | NSDayCalendarUnit |NSHourCalendarUnit|NSMinuteCalendarUnit;
    NSDateComponents *components = [calendar components:unitFlags fromDate:date];
    NSInteger minute = [components minute];
    return (int)minute;
}
//在当前日期前几天
- (NSUInteger)daysAgo {
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *components = [calendar components:(NSDayCalendarUnit) 
                                               fromDate:self
                                                 toDate:[NSDate date]
                                                options:0];
    return [components day];
}
//午夜时间距今几天
- (NSUInteger)daysAgoAgainstMidnight {
    // get a midnight version of ourself:
    NSDateFormatter *mdf = [[NSDateFormatter alloc] init];
    [mdf setDateFormat:@"yyyy-MM-dd"];
    NSDate *midnight = [mdf dateFromString:[mdf stringFromDate:self]];
    [mdf release];
    
    return (int)[midnight timeIntervalSinceNow] / (60*60*24) *-1;
}

- (NSString *)stringDaysAgo {
    return [self stringDaysAgoAgainstMidnight:YES];
}

- (NSString *)stringDaysAgoAgainstMidnight:(BOOL)flag {
    NSUInteger daysAgo = (flag) ? [self daysAgoAgainstMidnight] : [self daysAgo];
    NSString *text = nil;
    switch (daysAgo) {
        case 0:
            text = @"Today";
            break;
        case 1:
            text = @"Yesterday";
            break;
        default:
            text = [NSString stringWithFormat:@"%d days ago", daysAgo];
    }
    return text;
}

//返回一周的第几天(周末为第一天)
- (NSUInteger)weekday {
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *weekdayComponents = [calendar components:(NSWeekdayCalendarUnit) fromDate:self];
    return [weekdayComponents weekday];
}
//转为NSString类型的
+ (NSDate *)dateFromString:(NSString *)string {
    return [NSDate dateFromString:string withFormat:[NSDate dbFormatString]];
}

+ (NSDate *)dateFromString:(NSString *)string withFormat:(NSString *)format {
    NSDateFormatter *inputFormatter = [[NSDateFormatter alloc] init];
    [inputFormatter setDateFormat:format];
    NSDate *date = [inputFormatter dateFromString:string];
    [inputFormatter release];
    return date;
}

+ (NSString *)stringFromDate:(NSDate *)date withFormat:(NSString *)format {
    return [date stringWithFormat:format];
}

+ (NSString *)stringFromDate:(NSDate *)date {
    return [date string];
}

+ (NSString *)stringForDisplayFromDate:(NSDate *)date prefixed:(BOOL)prefixed {
    /* 
     * if the date is in today, display 12-hour time with meridian,
     * if it is within the last 7 days, display weekday name (Friday)
     * if within the calendar year, display as Jan 23
     * else display as Nov 11, 2008
     */
    
    NSDate *today = [NSDate date];
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *offsetComponents = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit |NSDayCalendarUnit) 
                                                     fromDate:today];
    
    NSDate *midnight = [calendar dateFromComponents:offsetComponents];
    
    NSDateFormatter *displayFormatter = [[NSDateFormatter alloc] init];
    NSString *displayString = nil;
    
    // comparing against midnight
    if ([date compare:midnight] == NSOrderedDescending) {
        if (prefixed) {
            [displayFormatter setDateFormat:@"'at' h:mm a"]; // at 11:30 am
        } else {
            [displayFormatter setDateFormat:@"h:mm a"]; // 11:30 am
        }
    } else {
        // check if date is within last 7 days
        NSDateComponents *componentsToSubtract = [[NSDateComponents alloc] init];
        [componentsToSubtract setDay:-7];
        NSDate *lastweek = [calendar dateByAddingComponents:componentsToSubtract toDate:today options:0];
        [componentsToSubtract release];
        if ([date compare:lastweek] == NSOrderedDescending) {
            [displayFormatter setDateFormat:@"EEEE"]; // Tuesday
        } else {
            // check if same calendar year
            NSInteger thisYear = [offsetComponents year];
            
            NSDateComponents *dateComponents = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit |NSDayCalendarUnit) 
                                                           fromDate:date];
            NSInteger thatYear = [dateComponents year];
            if (thatYear >= thisYear) {
                [displayFormatter setDateFormat:@"MMM d"];
            } else {
                [displayFormatter setDateFormat:@"MMM d, yyyy"];
            }
        }
        if (prefixed) {
            NSString *dateFormat = [displayFormatter dateFormat];
            NSString *prefix = @"'on' ";
            [displayFormatter setDateFormat:[prefix stringByAppendingString:dateFormat]];
        }
    }
    
    // use display formatter to return formatted date string
    displayString = [displayFormatter stringFromDate:date];
    [displayFormatter release];
    return displayString;
}

+ (NSString *)stringForDisplayFromDate:(NSDate *)date {
    return [self stringForDisplayFromDate:date prefixed:NO];
}

- (NSString *)stringWithFormat:(NSString *)format {
    NSDateFormatter *outputFormatter = [[NSDateFormatter alloc] init];
    [outputFormatter setDateFormat:format];
    NSString *timestamp_str = [outputFormatter stringFromDate:self];
    [outputFormatter release];
    return timestamp_str;
}

- (NSString *)string {
    return [self stringWithFormat:[NSDate dbFormatString]];
}

- (NSString *)stringWithDateStyle:(NSDateFormatterStyle)dateStyle timeStyle:(NSDateFormatterStyle)timeStyle {
    NSDateFormatter *outputFormatter = [[NSDateFormatter alloc] init];
    [outputFormatter setDateStyle:dateStyle];
    [outputFormatter setTimeStyle:timeStyle];
    NSString *outputString = [outputFormatter stringFromDate:self];
    [outputFormatter release];
    return outputString;
}
//返回周日的的开始时间
- (NSDate *)beginningOfWeek {
    // largely borrowed from "Date and Time Programming Guide for Cocoa"
    // we'll use the default calendar and hope for the best
    
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDate *beginningOfWeek = nil;
    BOOL ok = [calendar rangeOfUnit:NSWeekCalendarUnit startDate:&beginningOfWeek
                           interval:NULL forDate:self];
    if (ok) {
        return beginningOfWeek;
    } 
    
    // couldn't calc via range, so try to grab Sunday, assuming gregorian style
    // Get the weekday component of the current date
    NSDateComponents *weekdayComponents = [calendar components:NSWeekdayCalendarUnit fromDate:self];
    
    /*
     Create a date components to represent the number of days to subtract from the current date.
     The weekday value for Sunday in the Gregorian calendar is 1, so subtract 1 from the number of days to subtract from the date in question.  (If today's Sunday, subtract 0 days.)
     */
    NSDateComponents *componentsToSubtract = [[NSDateComponents alloc] init];
    [componentsToSubtract setDay: 0 - ([weekdayComponents weekday] - 1)];
    beginningOfWeek = nil;
    beginningOfWeek = [calendar dateByAddingComponents:componentsToSubtract toDate:self options:0];
    [componentsToSubtract release];
    
    //normalize to midnight, extract the year, month, and day components and create a new date from those components.
    NSDateComponents *components = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit |NSDayCalendarUnit)
                                               fromDate:beginningOfWeek];
    return [calendar dateFromComponents:components];
}
//返回当前天的年月日.
- (NSDate *)beginningOfDay {
    NSCalendar *calendar = [NSCalendar currentCalendar];
    // Get the weekday component of the current date
    NSDateComponents *components = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit |NSDayCalendarUnit) 
                                               fromDate:self];
    return [calendar dateFromComponents:components];
}
//返回该月的第一天
- (NSDate *)beginningOfMonth
{
    return [self dateAfterDay:-[self getDay] + 1];
}
//该月的最后一天
- (NSDate *)endOfMonth
{
    return [[[self beginningOfMonth] dateafterMonth:1] dateAfterDay:-1];
}
//返回当前周的周末
- (NSDate *)endOfWeek {
    NSCalendar *calendar = [NSCalendar currentCalendar];
    // Get the weekday component of the current date
    NSDateComponents *weekdayComponents = [calendar components:NSWeekdayCalendarUnit fromDate:self];
    NSDateComponents *componentsToAdd = [[NSDateComponents alloc] init];
    // to get the end of week for a particular date, add (7 - weekday) days
    [componentsToAdd setDay:(7 - [weekdayComponents weekday])];
    NSDate *endOfWeek = [calendar dateByAddingComponents:componentsToAdd toDate:self options:0];
    [componentsToAdd release];
    
    return endOfWeek;
}

+ (NSString *)dateFormatString {
    return @"yyyy-MM-dd";
}

+ (NSString *)timeFormatString {
    return @"HH:mm:ss";
}

+ (NSString *)timestampFormatString {
    return @"yyyy-MM-dd HH:mm:ss";
}

// preserving for compatibility
+ (NSString *)dbFormatString {
    return [NSDate timestampFormatString];
}
@end