Building Offline-First Mobile Apps with React Native

## The Challenge

When building DriverPro, the biggest challenge was ensuring drivers could track their mileage even in areas with poor connectivity. Many drivers work in rural areas or underground parking structures where cellular signal is unreliable.

The Solution: Offline-First Architecture

I implemented an offline-first architecture using several key technologies:

1. Local Storage with AsyncStorage

All trip data is stored locally first, then synced when connection is available:

const saveTrip = async (tripData) => { const existingTrips = await AsyncStorage.getItem('pending_trips'); const trips = existingTrips ? JSON.parse(existingTrips) : []; trips.push({ ...tripData, synced: false }); await AsyncStorage.setItem('pending_trips', JSON.stringify(trips)); }; ```

2. Battery-Efficient Geofencing

Using Expo's Location API with careful configuration to minimize battery drain:

await Location.startGeofencingAsync('TRIP_GEOFENCE', [{
  latitude: startLocation.lat,
  longitude: startLocation.lng,
  radius: 100,
  notifyOnEnter: false,
  notifyOnExit: true
}]);

3. Background Sync with Firebase

When connectivity returns, data syncs automatically:

NetInfo.addEventListener(state => {
  if (state.isConnected) {
    syncPendingTrips();
  }
});

Results

• App works reliably in areas with no signal
• Battery usage reduced by 40% compared to continuous GPS tracking
• Trip data is never lost, even if the app crashes

Key Takeaways

1. Always store data locally first
2. Use geofencing instead of continuous location tracking
3. Implement automatic sync when connection returns
4. Test extensively in airplane mode