Local storage and caching

The right local storage depends on the nature of the data:

• `shared_preferences` — small key-value pairs: theme choice, whether onboarding was seen, the last selected filter. It is not read synchronously; it loads once at startup
• SQLite (`sqflite`) or another database — structured data you need to query: order history, an offline cache
• The file system — images, documents, exported files
• Secure storage — tokens and passwords must not live in `shared_preferences`; that needs a package backed by the platform keychain/keystore

Caching strategy depends on the data too:

• Cache-first — show local data, then refresh in the background. Fast startup, at the cost of briefly showing stale data
• Network-first — try the network, fall back to local. For data where freshness matters: a bank balance, an order status
• Cache-only — offline mode

The part most often forgotten is invalidation: deciding when cached data has gone stale. The approaches are time-based (TTL), event-based (the user made a change) or version-based.