But I want to make it without server …
It’s certainly possible to do peer-to-peer synching but that just makes things harder. Syncing is a really hard problem in general. Peer-to-peer syncing adds additional complexities like:
User interface — iOS apps typically only run when they’re in the foreground, which means that your user interface ends up being kinda clunky because you need to bring the apps to the front on both devices in order to sync.
Security — This includes both on-the-wire privacy, authentication and authorisation.
Looking back at the syncing problem itself, iOS has no high-level APIs for that. There’s various building blocks (file system and database APIs, networking APIs, security APIs) but you’ll have to solve the core syncing problem yourself (read up on vector clocks, CRDTs, and so on) or work with some third-party library that does this (for example, Ensembles).
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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
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