日期Date

iOS-时间与日期详解http://www.jianshu.com/p/f8aab37a27ff
https://github.com/MatthewYork/DateTools
iOS日历、日期、时间的计算http://www.jianshu.com/p/692bb0a7269c
iOS开发tips之日期与星期的对应http://www.jianshu.com/p/804d22fd5180
判断NSDate是星期几和农历http://www.jianshu.com/p/5850a5d03b8f

NSDate的8小时问题：初始化一个NSDate时间[NSDate date]，获取的是零时区的时间（格林尼治的时间: 年-月-日 时:分:秒: +时区），而北京时间是东八区时间，因为时区不同，所以打印的时间相差了8小时。

NSDate *date = [NSDate date];
NSLog(@"date时间 = %@", date);

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss Z"];
NSString *dateStr = [formatter stringFromDate:date];
NSLog(@"字符串时间 = %@", dateStr);

2016-12-07 10:44:24.470 timeTest[32743:2995134] date时间 = 2016-12-07 02:44:24 +0000
2016-12-07 10:44:24.471 timeTest[32743:2995134] 字符串时间 = 2016-12-07 10:44:24 +0800

也可以设置时区，获取指定时区的字符串时间

NSDate *date = [NSDate date];
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
formatter.timeZone = [NSTimeZone timeZoneWithName:@"Asia/Shanghai"];//东八区时间
NSString *dateStr = [formatter stringFromDate:date];
NSLog(@"字符串时间 = %@", dateStr);

TimeToolsManger

#import <Foundation/Foundation.h>

#define DEFAULT_DATE_TEMPLATE_STRING @"yyyy-MM-dd HH:mm:ss"
#define DEFAULT_SHORT_DATE_TEMPLATE_STRING @"yyyy-MM-dd HH:mm"
#define SHORT_DATE_TEMPLATE_STRING @"yyyy-MM-dd"
#define HOUR_MINUT_TEMPLATE_STRING @"HH:mm"
#define DETAIL_DATE_TEMPLATE_STRING @"yyyy年MM月dd日"
#define MONTH_DATE_TEMPLATE_STRING @"yyyy-MM"

@interface TimeToolsManger : NSObject

/**
 *  获取单例对象
 */
+ (instancetype)shareToolsManager;

///日期格式转字符串
+ (NSString *)dateToString:(NSDate *)date withDateFormat:(NSString *)format;

///字符串转日期格式
+ (NSDate *)stringToDate:(NSString *)dateString withDateFormat:(NSString *)format;

///根据时间取得今天是星期几
+ (NSString*)weekdayStringFromDate:(NSDate*)inputDate ;

///根据当前时间获取下一个月的今天
+(NSString*)getNextMonth:(NSUInteger)number;

///根据当前时间获取上一个月的今天
+(NSString*)getLastMonth:(NSUInteger)number;

///以秒为整数值 时间戳->字符串
+ (NSString *)timeWithTimeIntervalString:(NSString *)timeString;

///以秒为整数值 获取当前时间戳
+ (NSString *)dateTimeIntervalString;

///聊天界面通过时间戳得到标准格式的字符串
+(NSString *)getMessageDateStringFromTimeInterval:(NSTimeInterval)TimeInterval andNeedTime:(BOOL)needTime;
+ (NSString*)getMessageDateString:(NSDate*)messageDate andNeedTime:(BOOL)needTime;
+(NSString *)getWeekdayWithNumber:(NSInteger)number;

///计算距离当前时间天数
+(NSString*)residueDays:(NSString*)dateString;

///计算距离未来时间天数
+(NSString*)futureDays:(NSString*)dateString;
@end

//
//  TimeToolsManger.m
//  test123
//
//  Created by 29 on 16/12/13.
//  Copyright © 2016年 aiitex. All rights reserved.
//

#import "TimeToolsManger.h"

@implementation TimeToolsManger

+ (instancetype)shareToolsManager {
    static TimeToolsManger *manager = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        manager = [[TimeToolsManger alloc] init];
    });
    return manager;
}

///根据时间取得今天是星期几

+ (NSString*)weekdayStringFromDate:(NSDate*)inputDate {
    
    NSArray *weekdays = [NSArray arrayWithObjects: [NSNull null], @"周日", @"周一", @"周二", @"周三", @"周四", @"周五", @"周六", nil];
    
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    
    NSTimeZone *timeZone = [[NSTimeZone alloc] initWithName:@"Asia/Shanghai"];
    
    [calendar setTimeZone: timeZone];
    
    NSCalendarUnit calendarUnit = NSCalendarUnitWeekday;
    
    NSDateComponents *theComponents = [calendar components:calendarUnit fromDate:inputDate];
    
    return [weekdays objectAtIndex:theComponents.weekday];
    
}

///根据当前时间获取下一个月的今天

+(NSString*)getNextMonth:(NSUInteger)number{
    NSDate * mydate = [NSDate date];
    NSDateFormatter * dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd"];
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    NSDateComponents *comps = nil;
    comps = [calendar components:NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitMonth fromDate:mydate];
    NSDateComponents *adcomps = [[NSDateComponents alloc] init];
    [adcomps setYear:0];
    [adcomps setMonth:number];
    [adcomps setDay:0];
    NSDate *newdate = [calendar dateByAddingComponents:adcomps toDate:mydate options:0];
    NSString *beforDate = [dateFormatter stringFromDate:newdate];
    return beforDate;
}

///根据当前时间获取上一个月的今天

+(NSString*)getLastMonth:(NSUInteger)number{
    NSDate * mydate = [NSDate date];
    NSDateFormatter * dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd"];
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    NSDateComponents *comps = nil;
    comps = [calendar components:NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitMonth fromDate:mydate];
    NSDateComponents *adcomps = [[NSDateComponents alloc] init];
    [adcomps setYear:0];
    [adcomps setMonth:-number];
    [adcomps setDay:0];
    NSDate *newdate = [calendar dateByAddingComponents:adcomps toDate:mydate options:0];
    NSString *beforDate = [dateFormatter stringFromDate:newdate];
    return beforDate;
}


///日期格式转字符串
+ (NSString *)dateToString:(NSDate *)date withDateFormat:(NSString *)format
{
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:format];
    NSString *strDate = [dateFormatter stringFromDate:date];
    return strDate;
}

///字符串转日期格式
+ (NSDate *)stringToDate:(NSString *)dateString withDateFormat:(NSString *)format
{
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:format];
    
    NSDate *date = [dateFormatter dateFromString:dateString];
    
    ///将世界时间转化为中国区时间
    NSTimeZone *timeZone = [NSTimeZone systemTimeZone];
    NSInteger interval = [timeZone secondsFromGMTForDate:date];
    NSDate *localeDate = [date  dateByAddingTimeInterval:interval];
    
    return localeDate;
}
///以秒为整数值的时间戳转换
+ (NSString *)timeWithTimeIntervalString:(NSString *)timeString
{
    NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
    formatter.timeZone = [NSTimeZone timeZoneWithName:@"Asia/Beijing"];
    [formatter setDateStyle:NSDateFormatterMediumStyle];
    [formatter setTimeStyle:NSDateFormatterShortStyle];
    [formatter setDateFormat:@"yyyy年MM月dd日 HH:mm:ss"];

    NSDate* date = [NSDate dateWithTimeIntervalSince1970:[timeString doubleValue]];
    NSString* dateString = [formatter stringFromDate:date];
    return dateString;
}

///以秒为整数值 获取当前时间戳
+ (NSString *)dateTimeIntervalString{
    NSDate* date = [NSDate dateWithTimeIntervalSinceNow:0];
    NSTimeInterval a=[date timeIntervalSince1970]; // *1000 是精确到毫秒，不乘就是精确到秒
    NSString *timeString = [NSString stringWithFormat:@"%.0f", a]; //转为字符型
    return timeString;
}

///聊天界面通过时间戳得到标准格式的字符串
+(NSString *)getMessageDateStringFromTimeInterval:(NSTimeInterval)TimeInterval andNeedTime:(BOOL)needTime
{
    NSDate *date = [NSDate dateWithTimeIntervalSince1970:TimeInterval];
    return [TimeToolsManger getMessageDateString:date andNeedTime:needTime];
}

+ (NSString*)getMessageDateString:(NSDate*)messageDate andNeedTime:(BOOL)needTime
{
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setLocale:[NSLocale systemLocale]];
    [formatter setTimeZone:[NSTimeZone systemTimeZone]];
    [formatter setDateFormat:@"YYYY/MM/dd HH:mm"];
    
    NSCalendar *cal = [NSCalendar currentCalendar];
    NSDateComponents *components = [cal components:NSCalendarUnitEra|NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay|NSCalendarUnitWeekday fromDate:messageDate];
    NSDate *msgDate = [cal dateFromComponents:components];
    
    NSString*weekday = [TimeToolsManger getWeekdayWithNumber:components.weekday];
    
    components = [cal components:NSCalendarUnitEra|NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay|NSCalendarUnitWeekday fromDate:[NSDate date]];
    NSDate *today = [cal dateFromComponents:components];
    
    if([today isEqualToDate:msgDate]){
        if (needTime) {
            [formatter setDateFormat:@"今天 HH:mm"];
        }
        else{
            [formatter setDateFormat:@"今天"];
        }
        return [formatter stringFromDate:messageDate];
    }
    
    components.day -= 1;
    NSDate *yestoday = [cal dateFromComponents:components];
    if([yestoday isEqualToDate:msgDate]){
        if (needTime) {
            [formatter setDateFormat:@"昨天 HH:mm"];
        }
        else{
            [formatter setDateFormat:@"昨天"];
        }
        return [formatter stringFromDate:messageDate];
    }
    
    for (int i = 1; i <= 6; i++) {
        components.day -= 1;
        NSDate *nowdate = [cal dateFromComponents:components];
        if([nowdate isEqualToDate:msgDate]){
            if (needTime) {
                [formatter setDateFormat:[NSString stringWithFormat:@"%@ HH:mm",weekday]];
            }
            else{
                [formatter setDateFormat:[NSString stringWithFormat:@"%@",weekday]];
            }
            return [formatter stringFromDate:messageDate];
        }
    }
    
    while (1) {
        components.day -= 1;
        NSDate *nowdate = [cal dateFromComponents:components];
        if ([nowdate isEqualToDate:msgDate]) {
            if (!needTime) {
                [formatter setDateFormat:@"YYYY/MM/dd"];
            }
            return [formatter stringFromDate:messageDate];
            break;
        }
    }
}

//1代表星期日、如此类推
+(NSString *)getWeekdayWithNumber:(NSInteger)number
{
    switch (number) {
        case 1:
            return @"星期日";
            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:
            return @"";
            break;
    }
}

///计算距离当前时间天数
+(NSString*)residueDays:(NSString*)dateString{
    NSDateFormatter * dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd"];
    NSDate *date1 = [dateFormatter dateFromString:dateString];
    NSDate *date  = [dateFormatter dateFromString:[TimeToolsManger dateToString:[NSDate date] withDateFormat:@"yyyy-MM-dd"]];
    NSTimeInterval time = [date timeIntervalSinceDate:date1];
    int days = ((int)time)/(3600*24);
    NSString *dateContent = [[NSString alloc] initWithFormat:@"%i",days];
    return dateContent;
}

///计算距离未来时间天数
+(NSString*)futureDays:(NSString*)dateString{
    NSDateFormatter * dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd"];
    NSDate *date1 = [dateFormatter dateFromString:dateString];
    NSDate *date  = [dateFormatter dateFromString:[TimeToolsManger dateToString:[NSDate date] withDateFormat:@"yyyy-MM-dd"]];
    NSTimeInterval time = [date1 timeIntervalSinceDate:date];
    int days = ((int)time)/(3600*24);
    NSString *dateContent = [[NSString alloc] initWithFormat:@"%i",days];
    return dateContent;
}
@end