Users expect apps to work everywhere — subway, airplane, poor 3G. Here's how we deliver.
The Core Pattern
Every offline-first app needs three things:
- Local data storage (SQLite or Realm)
- Background sync (when connection returns)
- Conflict resolution (when data changes offline)
Implementation Strategy
We use a queue-based sync system:
- User actions write to local DB immediately
- Operations queue for sync
- Background process syncs when online
- UI shows sync status clearly
The Sync Problem
What happens when two devices edit the same data offline? You need a conflict resolution strategy:
- Last Write Wins: Simple but loses data
- Operational Transform: Complex but perfect
- CRDTs: Middle ground (our choice)
Testing Offline
Turn off your WiFi. Use your app. If it breaks, fix it. Repeat until it doesn't break.
We test on real devices with network throttling to simulate poor connections.