Question

i have an iphone app that uses coredata to store its contents. users often ask me if i could provide a way to sync data between their mobile devices (ipod/iphone/ipad). as of now, i have no idea on how to achieve this.
i found zsync, but this seems to depend on a osx version of the app (which i dont have). i also read about upcoming iclouds sync features, and it seems to be what i need – however i think its not possible to sync coredata contents, but text-based contents only (e.g. xml storage files). is this true?

another way i was thinking of was to abuse the eventkit api to sync via a user-provided calendar. since my app is mainly managing events, which can optionally be stored in a user-calendar (in addition to coredata storage), syncing through a calendar would seem good to me. however i think syncing might break, e.g. when the user chooses not to syncronize the whole calendar but only like 3 months in the devices settings/account settings.

anyone got an idea of how my approach should be like? any tips?

Answer 1

Syncing device to device (if that is what you are trying to achieve) can be quite tricky. You could implement your own discovery and data-transfer protocol and work something out that way, but it could be quite a bit of work.

Syncing device to server to device is a bit more straightforward, assuming that you already have a server with some form of registration/login system. Then you just need a way of communicating your current database state up to the server, and then back down again from the server to other devices. Again there is a fair bit of work involved in doing this, but at least the logic of working out which devices sync with which other devices and how they transfer data from one to the other is all implicit in the workings of the server.

As for iCloud, the programmatic content that you sync through it needs to be derived from UIDocument, so it will not help you with generic Core Data entities.

If you’re looking for an out-of-the-box solution that will sync all of your Core Data content from one device to another with no custom code, then there really isn’t one. The closest you can reasonably get would be to ship the entire .sqlite file that your app uses from one device to another, overwriting the target devices .sqlite file. That works fine if your sync only needs to be unidirectional, but obviously is not appropriate for other use-cases. Perhaps you could use this model with iCloud, if you can get it to sync your app’s entire .sqlite file as an atomic entity.