How to store local data after user delete my iOS app?

Question

I thought it's impossible, because all the data store in a sandbox, when user delete the app, all the data should be removed from the device.

But somehow, this happened:

I downloaded a wallpaper app from the appstore.

It's a free app, if you don't pay, you can download limited wallpapers, up to 105.

I download a wallpaper and save to my album. it's now 1/105.
I delete the app, and delete the wallpaper in my album.
I turn off the iCloud backup function. OK, It's totally removed from my device, right?
I download it again.
I enter flight mode, so there is no internet connection.
I open the app, no wallpaper preview can be download from internet.

But the save count shows 1/105!

I'm not trying to steal their wallpapers, I did not change my wallpaper for 4 months. I just wanna know, how can this app know I saved 1 wallpaper already?

I delete the app. so it's not store in the app documents or tmp folder.
I delete the wallpaper in my album, SO it can't get it from an MD5 of my album.
I am in flight mode, so it can't get it from their server or anywhere on the internet.

Anyone knows where this app stored the save/download count?

it's certainly not on your device - it could be stored on their own servers — bshirley, Feb 07 '12 at 16:52
@bshirley NOT their own server, notice that I enter the flight mode. — EggErr, Feb 08 '12 at 00:11
@jrturton My real question is: how to store data outside the sandbox — EggErr, Feb 08 '12 at 00:12
@RichardJ.RossIII omg, I'm in China, how could I know those people, My real question is, how they can remember my download count. it's NOT an AD. Thanks for the editing, sorry for my bad english :( — EggErr, Feb 08 '12 at 00:13

score 16 · Accepted Answer · answered Feb 08 '12 at 04:27

16

This is done using the keychain on iOS most likely.

Read up on it here: https://developer.apple.com/library/mac/documentation/security/Reference/keychainservices/Reference/reference.html

answered Feb 08 '12 at 04:27

Richard J. Ross III

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Thank you Richard! I think you're right! Follow your clue, I found this: Uninstalling an application will not remove the items from the keychain. If you run the demo application on your device, and uninstall the app, the username and password will remain in the keychain (a firmware reset will, of course, remove the keychain values). – EggErr Feb 09 '12 at 01:42
3

This behavior has changed - just in case anyone from the future finds this page: https://stackoverflow.com/questions/18911434/will-items-in-ios-keychain-survive-app-uninstall-and-reinstall – cbartondock Jul 11 '17 at 19:33

How to store local data after user delete my iOS app?

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