做App避免不了要和时间打交道，关于时间的处理，里面有不少门道，远不是一行API调用，获取当前系统时间这么简单。我们需要了解与时间相关的各种API之间的差别，再因场景而异去设计相应的机制。

• 当前时间是否在fromHour和toHour之间
  * @brief 判断当前时间是否在fromHour和toHour之间。如， fromHour=8，toHour=23时，即为判断当前时间是否在8:00-23:00之间
  - (BOOL)isBetweenFromHour:(NSInteger)fromHour toHour:(NSInteger)toHour
  {
  NSDate *fromData = [self getCustomDateWithHour:fromHour];
  NSDate *toData = [self getCustomDateWithHour:toHour];

      NSDate *currentDate = [NSDate date];
  
      if ([currentDate compare:fromData] == NSOrderedDescending && [currentDate compare:toData] == NSOrderedAscending)
      {
          NSLog(@"该时间在 %ld:00-%ld:00 之间！", (long)fromHour, (long)toHour);
          return YES;
      }
      return NO;
  }
  

• 生成当天的某个点
  * @brief 生成当天的某个点（返回的是伦敦时间，可直接与当前时 间[NSDate date]比较）
  * @param hour 如hour为“8”，就是上午8:00（本地时间）
  - (NSDate *)getCustomDateWithHour:(NSInteger)hour
  {
  //获取当前时间
  NSDate *currentDate = [NSDate date];
  NSCalendar *currentCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
  NSDateComponents *currentComps = [[NSDateComponents alloc] init];

      NSInteger unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekdayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
  
      currentComps = [currentCalendar components:unitFlags fromDate:currentDate];
  
      //设置当天的某个点
      NSDateComponents *resultComps = [[NSDateComponents alloc] init];
      [resultComps setYear:[currentComps year]];
      [resultComps setMonth:[currentComps month]];
      [resultComps setDay:[currentComps day]];
      [resultComps setHour:hour];
  
      NSCalendar *resultCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
      return [resultCalendar dateFromComponents:resultComps];
  

}

• 字符串转时间
  * @param dateString 时间字符串
  * @param format 字符串格式 yyyy-MM-dd HH:mm:ss
  + (NSDate *)stringToDate:(NSString *)dateString format:(NSString *)format {
  NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
  [dateFormatter setDateFormat: format];
  NSDate *destDate= [dateFormatter dateFromString:dateString];
  return destDate;
  }

• 时间转字符串
  + (NSString *)dateToString:(NSDate *)date format:(NSString )format {
  NSDateFormatter dateFormat = [[NSDateFormatter alloc] init];
  [dateFormat setDateFormat:format];
  NSString *dateString = [dateFormat stringFromDate:date];
  return dateString;
  }

• 时间差
  + (NSTimeInterval)timeIntervalBetween:(NSDate *)beginDate and:(NSDate *)endDate
  {
  NSTimeInterval begin = [beginDate timeIntervalSince1970];
  NSTimeInterval end = [endDate timeIntervalSince1970];
  NSTimeInterval sub = end - begin;
  return sub;
  }

• 生成时间戳 （时间戳:从1970年1月1号 00:00:00开始走过的毫秒数）
  +(NSString *)createTimestamp
  {
  NSDate *datenow=[NSDate date];
  NSTimeZone *zone = [NSTimeZone systemTimeZone];
  NSInteger interval = [zone secondsFromGMTForDate:datenow];
  NSDate *localeDate = [datenow dateByAddingTimeInterval: interval];
  return [NSString stringWithFormat:@"%ld",(long)[localeDate timeIntervalSince1970]];
  }

• 时间转时间戳
  + (NSString *)parseParamDate:(NSDate *)date
  {
  NSTimeInterval time = [date timeIntervalSince1970] * 1000;
  return [NSString stringWithFormat:@"\/Date(%lld+0800)\/", (long long)time];
  }

• 时间戳转时间
  + (NSDate *)getDate:(NSString *)jsonValue
  {
  NSRange range = [jsonValue rangeOfString:@"\d{13}" options:NSRegularExpressionSearch];
  if (range.location == NSNotFound) {
  return nil;
  }
  NSString *value = [jsonValue substringWithRange:range];
  NSDate *result = [NSDate dateWithTimeIntervalSince1970:[value doubleValue]/1000];
  return result;
  }

• 将本地日期字符串转为UTC日期字符串
  //本地日期格式:2013-08-03 12:53:51
  //可自行指定输入输出格式
  -(NSString *)getUTCFormateLocalDate:(NSString *)localDate
  {
  NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
  //输入格式
  [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

      NSDate *dateFormatted = [dateFormatter dateFromString:localDate];  
      NSTimeZone *timeZone = [NSTimeZone timeZoneWithName:@"UTC"];  
      [dateFormatter setTimeZone:timeZone];  
      //输出格式  
      [dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ssZ"];  
      NSString *dateString = [dateFormatter stringFromDate:dateFormatted];  
      return dateString;  
  }  
  

• 将UTC日期字符串转为本地时间字符串
  //输入的UTC日期格式2013-08-03T04:53:51+0000
  -(NSString *)getLocalDateFormateUTCDate:(NSString *)utcDate
  {
  NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
  //输入格式
  [dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ssZ"];
  NSTimeZone *localTimeZone = [NSTimeZone localTimeZone];
  [dateFormatter setTimeZone:localTimeZone];

     NSDate *dateFormatted = [dateFormatter dateFromString:utcDate];  
     //输出格式  
     [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];  
     NSString *dateString = [dateFormatter stringFromDate:dateFormatted];  
     return dateString;  
  }  
  

时间描述

  #import <Foundation/Foundation.h>

  @interface NSDate (CZH)
  /// 日期描述字符串
  /// 格式如下
  ///     -   刚刚(一分钟内)
  ///     -   X分钟前(一小时内)
  ///     -   X小时前(当天)
  ///     -   昨天 HH:mm(昨天)
  ///     -   MM-dd HH:mm(一年内)
  ///     -   yyyy-MM-dd HH:mm(更早期)
  - (NSString *)czh_dateDescription;

  @end



  #import "NSDate+CZH.h"

  @implementation NSDate (CZH)
  - (NSString *)czh_dateDescription
  {

      // 1. 获取当前日历
      NSCalendar *calendar = [NSCalendar currentCalendar];

     // 2. 判断是否是今天
      if ([calendar isDateInToday:self]) {
          NSInteger interval = ABS((NSInteger)[self timeIntervalSinceNow]);
          if (interval < 60) {
              return @"刚刚";
          }
          interval /= 60;
          if (interval < 60) {
              return [NSString stringWithFormat:@"%zd 分钟前", interval];
          }
          return [NSString stringWithFormat:@"%zd 小时前", interval / 60];
      }

      // 3. 昨天
      NSMutableString *formatString = [NSMutableString stringWithString:@" HH:mm"];
      if ([calendar isDateInYesterday:self]) {
          [formatString insertString:@"昨天" atIndex:0];
      } else {
          [formatString insertString:@"MM-dd" atIndex:0];
    
          // 4. 是否当年
          NSDateComponents *components = [calendar components:NSCalendarUnitYear fromDate:self toDate:[NSDate date] options:0];
          if (components.year != 0) {
              [formatString insertString:@"yyyy-" atIndex:0];
          }
      }

      // 5. 转换格式字符串
      NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
      fmt.locale = [NSLocale localeWithLocaleIdentifier:@"en"];
      fmt.dateFormat = formatString;

      return [fmt stringFromDate:self];
  }
  @end