is it possible to degrade Open journal System to older version? if yes, does the content remains as it is or all information will lose?
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As title.
Is it possible that files that I store in the NSCachesDirectory can be deleted by the system (i.e. in low storage situations), while my is running in the foreground?
File System programming guide
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.
So the answer is - No, it is not possible for the NSCachesDirectory to be deleted while the app is running in the foreground.
However their wording is slightly ambiguous with regard to the app running in the background.
As of iOS 5.0 Apple began to purge or clean the Caches directory inside individual applications when it decided the device was using too much space. Can anyone point me to the location of documentation or anecdotal information regarding at which threshold this cache cleaning occurs (for instance 90%+ disk usage) and how often it is checked?
From my my testing, it seems that the wipe happens to all not currently running applications when the space usage on the device EXCEEDS the reported amount of space available (seems iPhone lies about space available to prevent you from getting into reserved space). When you cross that line, a dialogue pops up:
And when you hit done, it then wipes the space. This is the only situation that I was able to reliably reproduce to trigger the wipe (for testing / etc), and I did so by filling my device as much as I could with movies and music, and then downloading big files in DropBox.
as far as i know there hasn't been any official information about when the purge happens and - to be honest - you shouldn't be trying to predict it. it IS a problem, though. thankfully, apple has realised this and as of iOS 5.0.1 you can set a "do not backup" flag:
http://developer.apple.com/library/ios/#qa/qa1719/_index.html
so you'll want to place those files in your app's Documents/ dir or your apps Library/Private Documents/ and set the "do not backup" attribute.
Is there any limit on the physical memory size (file system) one can utilize in a iPhone application. My concern is what if someone keeps on writing some data files in the Documents folders and do not purge it. And the data can be of any size.
The only hard storage limit is that of the total available space on the iOS device.
The scenario you have described is likely reality... there is a feature in the upcoming version of iOS that will assist in managing this issue, but it's still under NDA so cannot be discussed here. (yet)
EDIT: And in iOS 5, on your device you can now go to Settings -> Usage to get a list of all installed apps on your phone/pad/pod and see how much extra space they are consuming. :)
You can use ASL or GTMLogger to manage your log files.
Some links that might be handy for you:
Best Practices for Error Logging and/or reporting for iPhone
objective-c logging best practices
I'm not talking about binary size. I'm talking about the amount of data that can be written to disk during execution inside of certain directories such as Cache or Documents.
I can't find an easy answer in the XCode documentation, which is to say I can find none at all.
I know there is a limit for the cache directory in the form of "oh hey, your device is crashing now", but I haven't determined the actual number, and I am not sure if the Documents folders or other folders have the same restrictions.
Links and numbers are appreciated!
There is no reference or limitation of disk space once the application has been installed to the iPhone, iPad, or iPod Touch device.
The only limitation would be available disk space (whole disk space available) at time of writing to those directories.
I am not sure, but I think I was reading a while ago that iPhone / iPod Touch don't cache anything to disk. They cache only in memory. So cache is not persistet when app quits. After relaunch of app it will re-fetch the data from the net. Is that true?
iPhone OS disables on-disk caching from NSURLCache on this platform. If you need on-disk caching support anyway, you can use http://github.com/rs/SDURLCache which gives back on-disk cache support on iPhone OS
You can explore this yourself using the iPhone Simulator, opening a terminal or using the Finder, and going to `~Library/Application Support/iPhone Simulator/User/Applications/ then opening whatever directory your application is in.
You'll see a Documents directory, a Library and a tmp directory.
I've never looked to see if UIWebView is caching anything, but I know that Core Data will.
If you just suck down data yourself using CFNetwork, I believe it's up to you to cache the data yourself by saving it to tmp or Documents if you want.
tmp will not get backed up by the iTunes Sync process, but Documents will, so don't use Documents for temporary cache. Otherwise you'll just waste space and slow down sync backups.
The Documents directory will persist through anything, including app upgrades, except outright deleting the application using the Springboard or doing a total device storage wipe.
Actually the Library directory has directories. called Cache, WebKit/LocalStorage, and Preferences. So that would suggest something or the other.
Don't write to the application bundle directory or bad things could happen.
iPhone apps can write data to disk.