iPhone - 获取给定地点/时区的当前日期和时间的正确方法，并将其与同一地点的其他日期/时间进行比较

3 回答

• 34

  我正在寻找正确的方法来获得给定地点/时区的实际日期和时间 .

  [NSDate date] 返回表示当前日期和时间的日期对象，无论您身在何处 . NSDate s不受地点或时区限制 . 现在只有一个NSDate或任何其他时刻表示，而不是每个时区的不同日期对象 . 因此，您不应尝试在时区之间转换日期 .

  NSDate 对象表示 absolute 及时 . 请考虑以下示例，说明不同时区（巴黎的 9/9/11 3:54 PM 和悉尼的 9/9/11 11:54 PM ）中的两个日期表示实际上是同一个日期 .

  NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
  [formatter setDateStyle:NSDateFormatterShortStyle];
  [formatter setTimeStyle:NSDateFormatterShortStyle];
  [formatter setTimeZone:[NSTimeZone timeZoneWithName:@"Europe/Paris"]];
  NSDate *aDate = [formatter dateFromString:@"9/9/11 3:54 PM"];
  [formatter setTimeZone:[NSTimeZone timeZoneWithName:@"Australia/Sydney"]];
  NSDate *anotherDate = [formatter dateFromString:@"9/9/11 11:54 PM"];
  NSLog(@"%@",anotherDate);
  if ([aDate isEqualToDate:anotherDate]) {
      NSLog(@"How about that?");
  }
  

  它记录了最后一条消息，因为巴黎的 9/9/11 3:54 PM 和悉尼的 9/9/11 11:54 PM 实际上是同一时刻 . 当它在巴黎 9/9/11 3:54 PM 时，它在悉尼是 9/9/11 11:54 PM .

  两者都在调试器和NSLog 2011-09-09 14:26:02中给出，但它现在是16:26所以我猜它应该返回16:26:02 0200

  在输出日期时，请记住 NSDate 的 description 方法在GMT中返回时间，您需要使用 NSDateFormatter 创建一个日期字符串，表示从日期开始在巴黎，悉尼等地的当地时间：

  NSDate *now = [NSDate date];
  NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
  [formatter setDateStyle:NSDateFormatterShortStyle];
  [formatter setTimeStyle:NSDateFormatterShortStyle];
  [formatter setTimeZone:[NSTimeZone timeZoneWithName:@"Australia/Sydney"]];
  NSLog(@"%@",[formatter stringFromDate:now]); //--> 9/9/11 11:54 PM
  [formatter setTimeZone:[NSTimeZone timeZoneWithName:@"Europe/Paris"]];
  NSLog(@"%@",[formatter stringFromDate:now]); //-->  9/9/11 3:54 PM
  

  ---

  好的，但如果我想知道这个时间是否在15:00之后，我该如何测试呢？

  创建一个今天15:00（当地时间）表示的NSDate对象，并将其与“now”进行比较：

  NSDate *now = [NSDate date];
  NSCalendar* myCalendar = [NSCalendar currentCalendar];
  NSDateComponents* components = [myCalendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit 
                                               fromDate:[NSDate date]];
  [components setHour: 15];
  [components setMinute: 0];
  [components setSecond: 0];
  NSDate *todayAt15 = [myCalendar dateFromComponents:components];
  if ([now compare:todayAt15] == NSOrderedDescending) {
      NSLog(@"After 15:00 local time");
  }
  

  ---

  事实证明@Oliver需要检查它是否是 after 15:00 in Paris 所以他需要创建一个代表今天巴黎时间15:00（不是当地时间）的日期 . 有关如何执行此操作的示例，请参阅@ Oliver的答案 . 为了清楚起见，我的第三段代码显示了如何检查它是否在当地时间15:00之后 .

  回复于 2024-04-27T18:06:37+08:00
• 9

  经过一番头痛并开始了解NSDate是什么之后，我想到了那种解决方案 . 您如何看待这种做法？

  // Now, an absolute date and time that represent now all around the world, that is made to play with
  NSDate *now = [NSDate date];
  
  // A specific calendar for a specific place in the world
  NSCalendar* parisCalendar = [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] autorelease];
  [parisCalendar setTimeZone:[NSTimeZone timeZoneWithName:@"Europe/Paris"]];
  
  // Now components seen from Paris
  NSDateComponents* componentsNowInParis = [parisCalendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit|NSHourCalendarUnit|NSMinuteCalendarUnit|NSSecondCalendarUnit|NSTimeZoneCalendarUnit fromDate:now];
  
  // Tricking a copy of "Now components seen from Paris" to force 15:00:00, in Paris
  NSDateComponents* componentsInParisAt15 = [[componentsNowInParis copy] autorelease];
  [componentsInParisAt15 setHour:15];
  [componentsInParisAt15 setMinute:0];
  [componentsInParisAt15 setSecond:0];
  
  // Getting an universal date reference that represent what could be 15:00:00 seen from paris, Or 19:00:00 from GMT+4
  NSDate* dateAt15 = [parisCalendar dateFromComponents:componentsInParisAt15];
  
  // We now have two universal dates that can be compared each other
  // If "now" is 16:00:00, those date will show a 60 minutes difference all around the world
  NSLog(@"%@", now);
  NSLog(@"%@", dateAt15);
  

  一些参考：http://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/DatesAndTimes/Articles/dtTimeZones.html#//apple_ref/doc/uid/20000185-SW4

  但是，据我所知和测试，那天/时间不可能是绝对的 . 它基于iPhone日期/时间/时区，这可能是错误的 .

  回复于 2024-04-27T18:06:37+08:00
• 12

  使用NSCalendar和 setTimeZone 方法 .

  NSDate *newDate;
  NSDateComponents *dateComponents = [[NSCalendar currentCalendar] components:~ NSTimeZoneCalendarUnit fromDate:[NSDate date]];
  
  newDate = [[NSCalendar currentCalendar] dateFromComponents:dateComponents];
  NSLog(@"newDate: %@", newDate);
  NSLog(@"newDate: %.0f", [newDate timeIntervalSinceReferenceDate]);
  

  newDate：2011-09-09 15:02:09 0000
  newDate：337273330

  [dateComponents setTimeZone:[NSTimeZone timeZoneWithName:@"Australia/Sydney"]];
  newDate = [[NSCalendar currentCalendar] dateFromComponents:dateComponents];
  NSLog(@"newDate: %@", newDate);
  NSLog(@"newDate: %.0f", [newDate timeIntervalSinceReferenceDate]);
  

  newDate：2011-09-09 00:52:03 0000
  newTimeInterval：337222930

  [dateComponents setTimeZone:[NSTimeZone timeZoneWithName:@"Europe/Paris"]];
  newDate = [[NSCalendar currentCalendar] dateFromComponents:dateComponents];
  NSLog(@"newDate: %@", newDate);
  NSLog(@"newDate: %.0f", [newDate timeIntervalSinceReferenceDate]);
  

  newDate：2011-09-09 08:52:03 0000
  newTimeInterval：337251730

  回复于 2024-04-27T18:06:37+08:00