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ios开发 日期时间指南

2018年08月07日 ⁄ 综合 ⁄ 共 7202字 ⁄ 字号 小 中 大 ⁄ 评论关闭

主要有3个类：

NSDate：表示一个绝对的时间点

NSCalendar：允许你展示一个特殊的日历，比如Gregorian（公历）或Hebrew历（包括中国农历），它提供了大部分的日期计算接口，并且允许你在NSDate和NSDateComponents之间转换

NSDateComponents允许你展示一个特殊日期的不同部分，比如hour，minute，day，year等等。

NSTimeZone表示时区信息

NSDateFormatter用来在日期和字符串之间转换

可以认为NSDate表示的是绝对的数值，而NSCalendar，NSTimeZone和NSDateFormatter则表示了怎么来解释这个数值。

NSDate：

NSDate是一个抽象的概念，独立于locals，timezones和calendars，也可以认为它表示的就是公历的GMT时间 （NSLog打印的时候都会显示GMT时间）。它的单位是NSTimeInterval，用秒来表示。NSDate用相对于2001年1月1日（GMT） 的秒来计算时间，早于这个时间用负值来表示，晚于这个时间为正值。NSDate的方法timeIntervalSinceReferenceDate就是
指相对于这个日期的秒数。

Listing 1 Creating dates with time intervals

NSTimeInterval secondsPerDay = 24 * 60 * 60;
 
NSDate *tomorrow = [[NSDate alloc]
 
initWithTimeIntervalSinceNow:secondsPerDay];
 
NSDate *yesterday = [[NSDate alloc]
 
initWithTimeIntervalSinceNow:-secondsPerDay];
 
[tomorrow release];
 
[yesterday release];

Listing 2 Creating dates by adding a time interval

NSTimeInterval secondsPerDay = 24 * 60 * 60;
 
NSDate *today = [[NSDate alloc] init];
 
NSDate *tomorrow, *yesterday;
 
tomorrow = [today dateByAddingTimeInterval: secondsPerDay];
 
yesterday = [today dateByAddingTimeInterval: -secondsPerDay];
 
[today release];

比较时间用isEqualToDate:, compare:, laterDate:和 earlierDate:方法，两个时间之间的间隔用timeIntervalSince...方法

NSCalendar和NSDateComponents：

Listing 3 Creating calendar objects

NSCalendar *currentCalendar = [NSCalendar currentCalendar];
 
NSCalendar *japaneseCalendar = [[NSCalendar alloc]
 
initWithCalendarIdentifier:NSJapaneseCalendar];
 
NSCalendar *usersCalendar =
 
[[NSLocale currentLocale] objectForKey:NSLocaleCalendar];

currentCalendar和usersCalendar都是用户本地的日历

Listing 4 Creating a date components object

NSDateComponents *components = [[NSDateComponents alloc] init];
 
[components setDay:6];
 
[components setMonth:5];
 
[components setYear:2004];
 
NSInteger weekday = [components weekday]; // Undefined (== NSUndefinedDateComponent)

在Dates和Date Components之间转换：

Listing 5 Getting a date’s components

NSDate *today = [NSDate date];
 
NSCalendar *gregorian = [[NSCalendar alloc]
 
initWithCalendarIdentifier:NSGregorianCalendar];
 
NSDateComponents *weekdayComponents =
 
[gregorian components:(NSDayCalendarUnit | NSWeekdayCalendarUnit) fromDate:today];
 
NSInteger day = [weekdayComponents day];
 
NSInteger weekday = [weekdayComponents weekday];

你需要用Calendar Units这个常量来指定要获取的部分。

NSCalendar的ordinalityOfUnit:inUnit:forDate:方法用来获取一个小的单位在一个大的单位里面的序数，比如你可以查看一个日期在一年中的天数。

Listing 6 Creating a date from components

NSDateComponents *components = [[NSDateComponents alloc] init];
 
[components setWeekday:2]; // Monday
 
[components setWeekdayOrdinal:1]; // The first Monday in the month
 
[components setMonth:5]; // May
 
[components setYear:2008];
 
NSCalendar *gregorian = [[NSCalendar alloc]
 
initWithCalendarIdentifier:NSGregorianCalendar];
 
NSDate *date = [gregorian dateFromComponents:components];

技术上来说不存在没有年的日期，如果你只想表示生日也可以不指定year：

Listing 7 Creating a yearless date

NSDateComponents *components = [[NSDateComponents alloc] init];
 
[components setMonth:11];
 
[components setDay:7];
 
NSCalendar *gregorian = [[NSCalendar alloc]
 
initWithCalendarIdentifier:NSGregorianCalendar];
 
NSDate *birthday = [gregorian dateFromComponents:components];

不过这样以后你取components的时候就要记得不能指定year。

Listing 8 Converting date components from one calendar to another

NSDateComponents *comps = [[NSDateComponents alloc] init];
 
[comps setDay:6];
 
[comps setMonth:5];
 
[comps setYear:2004];
 
NSCalendar *gregorian = [[NSCalendar alloc]
 
initWithCalendarIdentifier:NSGregorianCalendar];
 
NSDate *date = [gregorian dateFromComponents:comps];
 
[comps release];
 
[gregorian release];
 
NSCalendar *hebrew = [[NSCalendar alloc]
 
initWithCalendarIdentifier:NSHebrewCalendar];
 
NSUInteger unitFlags = NSDayCalendarUnit | NSMonthCalendarUnit |
 
NSYearCalendarUnit;
 
NSDateComponents *components = [hebrew components:unitFlags fromDate:date];
 
NSInteger day = [components day]; // 15
 
NSInteger month = [components month]; // 9
 
NSInteger year = [components year]; // 5764

日期计算：

你可以用dateByAddingComponents:toDate:options:方法给一个date增加一个date的部分（比如小时或者分钟）

Listing 9 An hour and a half from now

NSDate *today = [[NSDate alloc] init];
 
NSCalendar *gregorian = [[NSCalendar alloc]
 
initWithCalendarIdentifier:NSGregorianCalendar];
 
NSDateComponents *offsetComponents = [[NSDateComponents alloc] init];
 
[offsetComponents setHour:1];
 
[offsetComponents setMinute:30];
 
// Calculate when, according to Tom Lehrer, World War III will end
 
NSDate *endOfWorldWar3 = [gregorian dateByAddingComponents:offsetComponents
 
toDate:today options:0];

Listing 10 Getting the Sunday in the current week

NSDate *today = [[NSDate alloc] init];
 
NSCalendar *gregorian = [[NSCalendar alloc]
 
initWithCalendarIdentifier:NSGregorianCalendar];
 
// Get the weekday component of the current date
 
NSDateComponents *weekdayComponents = [gregorian components:NSWeekdayCalendarUnit
 
fromDate:today];
 








NSDateComponents *componentsToSubtract = [[NSDateComponents alloc] init];








[componentsToSubtract setDay: 0 - ([weekdayComponents weekday] - 1)];
















NSDate *beginningOfWeek = [gregorian dateByAddingComponents:componentsToSubtract








toDate:today options:0];
























NSDateComponents *components =








[gregorian components:(NSYearCalendarUnit | NSMonthCalendarUnit |








NSDayCalendarUnit) fromDate: beginningOfWeek];








beginningOfWeek = [gregorian dateFromComponents:components];











NSCalendar的rangeOfUnit:startDate:interval:forDate:方法可以按照rangeOfUnit指定的单位查找初始值，比如：



Listing 11 Getting the beginning of the week










NSDate *today = [[NSDate alloc] init];








NSDate *beginningOfWeek = nil;








BOOL ok = [gregorian rangeOfUnit:NSWeekCalendarUnit startDate:&beginningOfWeek








interval:NULL forDate: today];











Listing 12 Getting

 the difference between two dates










NSDate *startDate = ...;








NSDate *endDate = ...;
















NSCalendar *gregorian = [[NSCalendar alloc]








initWithCalendarIdentifier:NSGregorianCalendar];
















NSUInteger unitFlags = NSMonthCalendarUnit | NSDayCalendarUnit;
















NSDateComponents *components = [gregorian components:unitFlags








fromDate:startDate








toDate:endDate options:0];








NSInteger months = [components month];








NSInteger days = [components day];











Listing 15 Determining whether a date is this week










-(BOOL)isDateThisWeek:(NSDate *)date {








NSDate *start;








NSTimeInterval extends;








NSCalendar *cal=[NSCalendar autoupdatingCurrentCalendar];








NSDate *today=[NSDate date];








BOOL success= [cal rangeOfUnit:NSWeekCalendarUnit startDate:&start








interval: &extends forDate:today];








if(!success)return NO;








NSTimeInterval dateInSecs = [date timeIntervalSinceReferenceDate];








NSTimeInterval dayStartInSecs= [start timeIntervalSinceReferenceDate];








if(dateInSecs > dayStartInSecs && dateInSecs < (dayStartInSecs+extends)){








return YES;








}








else {








return NO;








}








}











Time Zones：



time zone会影响从calendar计算的date components，你可以设置NSCalendar的time zone。NSCalendar默认使用应用程序的时区。可以从timeZoneWithName:, timeZoneWithAbbreviation:, 和 timeZoneForSecondsFromGMT:方法获取一个NSTimeZone对象。可以用[NSTimeZone

 knownTimeZoneNames]方法获取所有time zone的数组。



可以用setDefaultTimeZone:方法设置默认的时区，用localTimeZone方法始终返回默认的时区。



Listing 16 Creating a date from components using a specific time zone










NSCalendar *gregorian=[[NSCalendar alloc] initWithCalendarIdentifier: NSGregorianCalendar];








[gregorian setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"CDT"]];








NSDateComponents *timeZoneComps=[[NSDateComponents alloc] init];








[timeZoneComps setHour:16];








//specify whatever day, month, and year is appropriate








NSDate *date=[gregorian dateFromComponents:timeZoneComps];











Date Formatters



有两个基本的方法：dateFromString: 和 stringFromDate:用来在日期和字符串之间转换



 



NSDateFormatter *formatter = [[NSDateFormatter alloc] init];



[formatter setTimeZone:[NSTimeZone systemTimeZone]];



[formatter setDateFormat:@"yyyy-MM-dd"];



NSDate *date = [formatter dateFromString:string];



[formatter release];



 



NSDateFormatter *formatter = [[NSDateFormatter alloc] init];



[formatter setTimeZone:[NSTimeZone systemTimeZone]];



[formatter setDateFormat:@"yyyy-MM-dd"];



NSString *dateString = [formatter stringFromDate:date];



[formatter release];















														

							

			

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