blocks|key|2948338|text|我们的经验是，此文件夹在应用程序更新时会被清除。如果能确切地知道这个文件夹何时是要清除的候选文件夹，那就太好了。文档将该文件夹描述为|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2948339|可丢弃缓存文件(库/缓存)的|2948340|位置|blockquote|2948341|2948342|2948343|应用程序更新时不会清除NSDocumentDirectory，但请小心使用此文件夹，因为iOS+5现在使用此文件夹在iCloud中进行备份，如果您使用此目录存储用户生成的内容以外的任何内容，则您的应用程序可能会被拒绝。|offset|length|style|CODE|2948344|entityMap^0|0|0|0|0|0|B|J|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$]]|$1|G|3|-4|5|6|7|T|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|V|8|@$K|W|L|X|M|N]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

Our experience is that this folder gets cleared on app updates. It would be nice to know when exactly this folder is a candidate for being cleared. The docs describe this folder as

<blockquote>
 location of discardable cache files (Library/Caches)
</blockquote>

The <code>NSDocumentDirectory</code> will not be cleared on app updates but be careful using this folder since iOS 5 now uses this folder for backing up in iCloud and your app will likely be rejected if you use this directory to store anything other then user generated content.

blocks|key|262681|text|在应用程序更新期间，iOS不会删除库文件夹中的任何内容。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|262682|请查看来自Apple的以下文档，其中提到：|262683|262684|当用户下载应用程序更新时，iTunes会将更新安装到新的应用程序目录中。然后，在删除旧安装之前，它会将用户的数据文件从旧安装移到新的app目录中。在更新过程期间，保证保留以下目录中的文件：|blockquote|offset|length|style|BOLD|262685|262686|应用程序_主页>/文档|262687|Application_Home>/Library|262688|尽管也可以移动其他用户目录中的文件，但您不应依赖它们在更新后仍然存在。|262689|262690|以下是指向此文档的链接：http://developer.apple.com/library/ios/#documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/PerformanceTuning/PerformanceTuning.html#//apple_ref/doc/uid/TP40007072-CH8-SW10|262691|希望这能有所帮助。|262692|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/library/ios/#documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/PerformanceTuning/PerformanceTuning.html#//apple_ref/doc/uid/TP40007072-CH8-SW10^0|0|0|0|29|D|0|0|0|B|0|0|P|0|0|Z|0|0|0|59|C|4X|0|0|0|9|0^^$0|@$1|2|3|4|5|6|7|15|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|16|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|17|8|@]|9|@]|A|$]]|$1|E|3|F|5|G|7|18|8|@$H|19|I|1A|J|K]]|9|@]|A|$]]|$1|L|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|1C|8|@$H|1D|I|1E|J|K]]|9|@]|A|$]]|$1|O|3|P|5|6|7|1F|8|@$H|1G|I|1H|J|K]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1I|8|@$H|1J|I|1K|J|K]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1L|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|1M|8|@$H|1N|I|1O|J|K]]|9|@$H|1P|I|1Q|1|1R]]|A|$]]|$1|V|3|W|5|6|7|1S|8|@$H|1T|I|1U|J|K]]|9|@]|A|$]]|$1|X|3|-4|5|6|7|1V|8|@]|9|@]|A|$]]]|Y|$Z|$5|10|11|12|A|$13|14]]]]

Anything which is in Library folder will NOT be deleted by the iOS during App Update.
Please check following documentation from Apple which mentions:
<blockquote>
When a user downloads an app update, iTunes installs the update in a new app directory. It then moves the user’s data files from the old installation over to the new app directory before deleting the old installation. Files in the following directories are guaranteed to be preserved during the update process:
Application_Home&gt;/Documents
Application_Home&gt;/Library
Although files in other user directories may also be moved over, you should not rely on them being present after an update.
</blockquote>
Here is the link to this documentation:
<a href="http://developer.apple.com/library/ios/#documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/PerformanceTuning/PerformanceTuning.html#//apple_ref/doc/uid/TP40007072-CH8-SW10" rel="noreferrer">http://developer.apple.com/library/ios/#documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/PerformanceTuning/PerformanceTuning.html#//apple_ref/doc/uid/TP40007072-CH8-SW10</a>
Hope this helps.

blocks|key|262730|text|在内存不足的情况下可以删除NSCachesDirectory|type|unstyled|depth|inlineStyleRanges|entityRanges|data|262731|262732|在iOS+5.0和更高版本上，当系统磁盘空间非常低时，系统在极少数情况下可能会删除缓存目录。在应用程序运行时，这种情况永远不会发生。但是，您应该知道，iTunes还原不一定是可以擦除缓存目录的唯一条件。|blockquote|262733|262734|262735|more+info|offset|length|262736|如果您不想删除您的文件，则必须将它们存储在Documents目录中，但这样做：|262737|使用“不备份”属性指定应保留在设备上的文件，即使在存储空间不足的情况下也是如此。将此属性用于可以重新创建但即使在存储空间较低的情况下也需要保留的数据，以便应用程序正常运行，或者因为客户希望它在脱机使用期间可用。此属性适用于标记的文件，而不管这些文件位于哪个目录中，包括文档目录。这些文件不会被清除，也不会包含在用户的iCloud或iTunes备份中。由于这些文件确实使用设备上的存储空间，因此您的应用程序负责定期监控和清除这些文件。|262738|more+info|262739|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.apple.com/library/prerelease/ios/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/FileSystemOverview/FileSystemOverview.html#//apple_ref/doc/uid/TP40010672-CH2-SW2|1|https://developer.apple.com/library/ios/#qa/qa1719/_index.html^0|0|0|0|0|0|0|9|0|0|0|0|0|9|1|0^^$0|@$1|2|3|4|5|6|7|11|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|12|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|13|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|14|8|@]|9|@]|A|$]]|$1|G|3|-4|5|6|7|15|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|16|8|@]|9|@$J|17|K|18|1|19]]|A|$]]|$1|L|3|M|5|6|7|1A|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|1B|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|1C|8|@]|9|@$J|1D|K|1E|1|1F]]|A|$]]|$1|R|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]]|S|$T|$5|U|V|W|A|$X|Y]]|Z|$5|U|V|W|A|$X|10]]]]

NSCachesDirectory can be deleted in cases of low memory

<blockquote>
 On iOS 5.0 and later, the system may delete the Caches directory on
 rare occasions when the system is very low on disk space. This will
 never occur while an app is running. However, you should be aware that
 iTunes restore is not necessarily the only condition under which the
 Caches directory can be erased.
</blockquote>

<a href="https://developer.apple.com/library/prerelease/ios/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/FileSystemOverview/FileSystemOverview.html#//apple_ref/doc/uid/TP40010672-CH2-SW2" rel="nofollow">more info</a>

If you don't want your files to be deleted you have to store them in the Documents directory, but this way:

Use the "do not back up" attribute for specifying files that should remain on device, even in low storage situations. Use this attribute with data that can be recreated but needs to persist even in low storage situations for proper functioning of your app or because customers expect it to be available during offline use. This attribute works on marked files regardless of what directory they are in, including the Documents directory. These files will not be purged and will not be included in the user's iCloud or iTunes backup. Because these files do use on-device storage space, your app is responsible for monitoring and purging these files periodically. 

<a href="https://developer.apple.com/library/ios/#qa/qa1719/_index.html" rel="nofollow">more info</a>

In what circumstances would files in the iOS NSCachesDirectory get removed? Obviously, delete and reinstall an application. What about application upgrade? What about low disk space conditions? Anything else?

When are files from NSCachesDirectory removed?

在什么情况下会删除iOS NSCachesDirectory中的文件？显然，删除并重新安装应用程序。那么应用程序升级呢？磁盘空间不足的情况会怎样？还要别的吗？

问何时从NSCachesDirectory中删除文件？
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