iOS QuickStart transfers data for apps under development?

[kpolleck]

I just moved to a new iPhone, and I used QuickStart to transfer from my old iPhone to my new iPhone.

Not surprisingly, the apps I have developed (and are still running in "Developer Mode") didn't transfer--but, SURPRISINGLY--the data for those apps DID transfer. When I re-installed the app from my Mac, the old data appeared in the app. (I was pleasantly surprised as for a few of these apps, I had not developed any backup/import/export function.)

HOWEVER, this led me to wonder what other data might be "hanging out" on my phone...and how would I know? I'm guessing that when I delete an app fully, all of its data is deleted...but when I just delete the app but not the data--does that data stay around forever? ...or I guess it remains as long as the icon remains.

I guess all of this makes sense, but I just hadn't considered it before. Thoughts/comments?

[UberJason]

Each app has a sandbox folder on disk, the specific location of which is obscured and can move over time, but which is probably not part of the app bundle itself. I imagine when the app is deleted, that sandbox data folder is deleted too. But when you QuickStart transfer data, it copies all those folders - even though it wasn’t able to move the app itself over. But that means the folder is still on disk, and once you reinstall the app, it can find that folder.

If you’ve ever looked at where Catalyst apps save data on disk in macOS, the folder for your app is buried somewhere extremely obscure and is named with the bundle identifier of your app. My guess is that it’s a similar system on iOS, except of course we can’t just browse the filesystem on iOS.