blocks|key|5560607|text|在Cocoa中使用时间可能很复杂。当您获取NSDate对象时，它位于本地时区。[[NSTimeZone+defaultTimeZone]+secondsFromGMT]提供当前时区与格林尼治标准时间的偏移量。然后你可以这样做：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5560608|NSDate+*localDate+=+//+get+the+date
NSTimeInterval+timeZoneOffset+=+[[NSTimeZone+defaultTimeZone]+secondsFromGMT];+//+You+could+also+use+the+systemTimeZone+method
NSTimeInterval+gmtTimeInterval+=+[localDate+timeIntervalSinceReferenceDate]+-+timeZoneOffset;
NSDate+*gmtDate+=+[NSDate+dateWithTimeIntervalSinceReferenceDate:gmtTimeInterval];|code-block|syntax|javascript|5560609|现在gmtDate应该有了格林尼治标准时间的正确日期。为了显示它，可以查看NSDateFormatter，特别是setDateStyle和setTimeStyle方法。您可以创建一个NSDateFormatter，按照您想要的方式对其进行配置，然后调用stringFromDate:以获得格式良好的字符串。|5560610|entityMap^0|L|6|13|19|0|0|2|7|11|F|1K|C|1X|C|2J|F|3I|F|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|N|$]]

Working with time in Cocoa can be complicated. When you get an <code>NSDate</code> object, it's in the local time zone. <code>[[NSTimeZone defaultTimeZone] secondsFromGMT]</code> gives you the offset of the current time zone from GMT. Then you can do this:

<pre><code>NSDate *localDate = // get the date
NSTimeInterval timeZoneOffset = [[NSTimeZone defaultTimeZone] secondsFromGMT]; // You could also use the systemTimeZone method
NSTimeInterval gmtTimeInterval = [localDate timeIntervalSinceReferenceDate] - timeZoneOffset;
NSDate *gmtDate = [NSDate dateWithTimeIntervalSinceReferenceDate:gmtTimeInterval];
</code></pre>

Now <code>gmtDate</code> should have the correct date in GMT for you. In order to display it, look at <code>NSDateFormatter</code>, specifically the <code>setDateStyle</code> and <code>setTimeStyle</code> methods. You create an <code>NSDateFormatter</code>, configure it the way you want, and then call <code>stringFromDate:</code> to get a nicely formatted string.

blocks|key|1633361|text|您是否尝试过查看NSDateFormatter的文档？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1633362|NSDateFormatter|offset|length|1633363|NSDateFormatter似乎有一些使用TimeZones的方法，特别是|1633364|-setTimeZone:|style|CODE|1633365|我没有亲自测试过它，但我想如果您将GMT设置为某个日期的时区，而该日期最初是用另一个时区表示的，那么它将显示经过正确调整以匹配新时区的日期。|1633366|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/iphone/library/documentation/Cocoa/Reference/Foundation/Classes/NSDateFormatter_Class/NSDateFormatter_Class.pdf^0|0|0|F|0|0|0|0|D|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|W|8|@]|9|@$D|X|E|Y|1|Z]]|A|$]]|$1|F|3|G|5|6|7|10|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|11|8|@$D|12|E|13|J|K]]|9|@]|A|$]]|$1|L|3|M|5|6|7|14|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|O|$P|$5|Q|R|S|A|$T|U]]]]

Have you tried looking at the documentation for NSDateFormatter? 

<a href="http://developer.apple.com/iphone/library/documentation/Cocoa/Reference/Foundation/Classes/NSDateFormatter_Class/NSDateFormatter_Class.pdf" rel="nofollow noreferrer">NSDateFormatter</a>

NSDateFormatter appears to have some methods for playing with TimeZones, particularly

<code>-setTimeZone:</code>

I haven't tested it myself, but I imagine that if you set GMT as the timezone on a date that is originally represented in another timezone, it will display the date with the correct adjustments to match the new timezone.

blocks|key|5560646|text|NSDateFormatter+*dateFormatter+=+[[NSDateFormatter+alloc]+init];
dateFormatter.dateFormat+=+@"yyyy-MM-dd'T'HH:mm";
++++++++
NSTimeZone+*gmt+=+[NSTimeZone+timeZoneWithAbbreviation:@"GMT"];
[dateFormatter+setTimeZone:gmt];
NSString+*timeStamp+=+[dateFormatter+stringFromDate:[NSDate+date]];
[dateFormatter+release];|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|5560647|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
dateFormatter.dateFormat = @&quot;yyyy-MM-dd'T'HH:mm&quot;;
 
NSTimeZone *gmt = [NSTimeZone timeZoneWithAbbreviation:@&quot;GMT&quot;];
[dateFormatter setTimeZone:gmt];
NSString *timeStamp = [dateFormatter stringFromDate:[NSDate date]];
[dateFormatter release];
</code></pre>

blocks|key|2033207|text|虽然Alex的回答是一个很好的开始，但它没有处理DST+(夏令时)，并添加了与参考日期之间不必要的转换。下面的方法对我很有效：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2033208|要将localDate转换为GMT，请考虑DST：|2033209|NSDate+*localDate+=+<<your+local+date>>
NSTimeInterval+timeZoneOffset+=+[[NSTimeZone+systemTimeZone]+secondsFromGMTForDate:localDate];
NSDate+*gmtDate+=+[localDate+dateByAddingTimeInterval:-timeZoneOffset];+//+NOTE+the+"-"+sign!|code-block|syntax|javascript|2033210|要将格林尼治标准时间日期转换为localDate，请执行以下操作：|2033211|NSDate+*gmtDate++=+<<your+gmt+date>>
NSTimeInterval+timeZoneOffset+=+[[NSTimeZone+systemTimeZone]+secondsFromGMTForDate:gmtDate];
NSDate+*localDate+=+[gmtDate+dateByAddingTimeInterval:timeZoneOffset];|2033212|注意:我使用的是dateByAddingTimeInterval，它只适用于iOS+4。如果您使用的是OS3或更早版本，请使用addTimerInterval。|2033213|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

While Alex's answer was a good start, it didn't deal with DST (daylight savings time) and added an unnecessary conversion to/from the reference date. The following works for me:

To convert from a localDate to GMT, taking DST into account:

<pre><code>NSDate *localDate = &lt;&lt;your local date&gt;&gt;
NSTimeInterval timeZoneOffset = [[NSTimeZone systemTimeZone] secondsFromGMTForDate:localDate];
NSDate *gmtDate = [localDate dateByAddingTimeInterval:-timeZoneOffset]; // NOTE the "-" sign!
</code></pre>

To convert from a GMT date to a localDate, taking DST into account:

<pre><code>NSDate *gmtDate = &lt;&lt;your gmt date&gt;&gt;
NSTimeInterval timeZoneOffset = [[NSTimeZone systemTimeZone] secondsFromGMTForDate:gmtDate];
NSDate *localDate = [gmtDate dateByAddingTimeInterval:timeZoneOffset];
</code></pre>

One small note: I used dateByAddingTimeInterval, which is iOS 4 only. If you are on OS 3 or earlier, use addTimerInterval.

blocks|key|2033236|text|+是正确的，请投票支持并接受它。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2033237|作为参考，我认为解释date对象和本地化的date表示之间的区别是有用的。|2033238|在许多编程语言中，date对象用于表示唯一的时间点。忽略Relativistic参数，可以假设在任何情况下，我们都可以定义一个对每个人都是通用的时间点，而不管我们如何测量时间。|2033239|如果对于每个时间点，我们可以构造一个唯一的标签，那么这个标签就可以被明确地传递和引用。+date对象的目的是充当给定时间点的唯一通用标签。|2033240|人们可以想出任何数量的技术来构建这样的标签方案，并且每个date对象如何选择这样做对任何使用它们的人来说都是无关紧要的。|2033241|例如，可以使用通用事件的数字偏移量(自太阳爆炸以来的X秒)。|2033242|只有当我们希望获取一个时间点并将其序列化为人类可读的字符串时，我们才必须处理时区、地区等的复杂性……|2033243|(本地日期字符串)%2B(日期格式化程序)+=>时间点|2033244|时间点%2B(日期格式化程序)+=>+(本地日期字符串)|2033245|每个时间点都是通用的..。没有纽约时间点或gmt+time+point，只有当您将一个时间点转换为本地字符串(使用日期格式化程序)时，才会出现与时区的任何关联。|2033246|注:我相信有很多关于这个问题的博客/文章，但我的google+foo在这个时候让我失望了。如果任何人有兴趣在这个问题上展开讨论，请随时这样做。|2033247|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Relativity_of_simultaneity^0|1|F|0|0|S|C|0|0|17|I|0|0|0|0|1|7|B|7|0|5|7|I|7|0|F|5|L|E|0|0|1Z|0^^$0|@$1|2|3|4|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1A|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|1B|8|@]|D|@$9|1C|A|1D|1|1E]]|E|$]]|$1|J|3|K|5|6|7|1F|8|@$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|L|3|M|5|6|7|1I|8|@]|D|@]|E|$]]|$1|N|3|O|5|6|7|1J|8|@]|D|@]|E|$]]|$1|P|3|Q|5|6|7|1K|8|@]|D|@]|E|$]]|$1|R|3|S|5|6|7|1L|8|@$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]]|D|@]|E|$]]|$1|T|3|U|5|6|7|1Q|8|@$9|1R|A|1S|B|C]|$9|1T|A|1U|B|C]]|D|@]|E|$]]|$1|V|3|W|5|6|7|1V|8|@$9|1W|A|1X|B|C]|$9|1Y|A|1Z|B|C]]|D|@]|E|$]]|$1|X|3|Y|5|6|7|20|8|@$9|21|A|22|B|C]]|D|@]|E|$]]|$1|Z|3|-4|5|6|7|23|8|@]|D|@]|E|$]]]|10|$11|$5|12|13|14|E|$15|16]]]]

<a href="https://stackoverflow.com/questions/1862905/nsdate-convert-date-to-gmt/2058602#2058602">Howard's Answer</a> is correct and please vote it up and accept it. 

For reference I think it is useful to explain the difference between date objects and localised date representations are.

In many programming languages date objects are used to represent unique points in time. Ignoring <a href="http://en.wikipedia.org/wiki/Relativity_of_simultaneity" rel="nofollow noreferrer">Relativistic</a> arguments it can be assumed that at any instance we can define a point in time which is equal universally for every one, regardless of how we measure time.

If for each point in time we could construct a unique label, that label could be passed around and referenced unambiguously. The purpose of date objects is to act as a unique universal label for a given point in time.

One could come up with any number of techniques to construct such a labelling scheme and how each date object chooses to do so is immaterial to anyone using them.

An example may be to use a numeric offset from a universal event (X seconds since the sun exploded).

It is only when we wish to take a time point and serialize it into a human readable string that we must deal with the complexities of time zones, locales, etc...

(Local Date String) + (Date Formatter) => Time Point

Time Point + (Date Formatter) => (Local Date String)

Every time point is universal... there is no such thing as a new york time point, or gmt time point, only once you convert a time point to a local string (using a date formatter) does any association to a time zone appear.

Note: I'm sure there are many blogs/articles on this very issue, but my google foo is failing me at this hour. If anyone has the enthusiasm to expand on this issue please feel free to do so.

blocks|key|5560746|text|Swift+4：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|5560747|//UTC+or+GMT+⟺+Local+

extension+Date+{

++++//+Convert+local+time+to+UTC+(or+GMT)
++++func+toGlobalTime()+->+Date+{
++++++++let+timezone+=+TimeZone.current
++++++++let+seconds+=+-TimeInterval(timezone.secondsFromGMT(for:+self))
++++++++return+Date(timeInterval:+seconds,+since:+self)
++++}

++++//+Convert+UTC+(or+GMT)+to+local+time
++++func+toLocalTime()+->+Date+{
++++++++let+timezone+=+TimeZone.current
++++++++let+seconds+=+TimeInterval(timezone.secondsFromGMT(for:+self))
++++++++return+Date(timeInterval:+seconds,+since:+self)
++++}

}|code-block|syntax|javascript|5560748|entityMap^0|0|7|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Swift 4: 

<pre><code>//UTC or GMT ⟺ Local 

extension Date {

 // Convert local time to UTC (or GMT)
 func toGlobalTime() -&gt; Date {
 let timezone = TimeZone.current
 let seconds = -TimeInterval(timezone.secondsFromGMT(for: self))
 return Date(timeInterval: seconds, since: self)
 }

 // Convert UTC (or GMT) to local time
 func toLocalTime() -&gt; Date {
 let timezone = TimeZone.current
 let seconds = TimeInterval(timezone.secondsFromGMT(for: self))
 return Date(timeInterval: seconds, since: self)
 }

}
</code></pre>

I need the ability to convert an <code>NSDate</code> value to a GMT Date.

How can I go about converting an <code>NSDate</code> value to a GMT formatted <code>NSDate</code> value, independent of whatever date locale settings the iPhone device is using?

NSDate - Convert Date to GMT

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我需要的能力，以转换格林尼治标准时间值到一个NSDate日期。如何将NSDate值转换为NSDate格式的GMT值，而与iPhone设备使用的日期区域设置无关？

问NSDate -将日期转换为GMT
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