Dev Flutter Platform Independence

Flutter & Platform Independence

Why Flutter

Tankstellen needs:

• One codebase, many platforms (Android now, iOS planned, desktop possible)
• Consistent UI — the same interaction whether on a 5" Android or a tablet
• No platform-specific forks of business logic, price parsing, service chains

Flutter fits because:

1. Rendering is owned by Flutter, not the OS. Every country's station card looks identical, including non-Latin scripts (Greek, Cyrillic).
2. Dart's async model handles the 11-country API reality cleanly: no thread gymnastics, no green-thread debugging, just async/await and Stream.
3. Material 3 + FlexColorScheme provides a theme that respects both Material Android expectations and Cupertino iOS guidelines where it matters.
4. Hot reload shortens iteration cycles from 30 s (native Android) to <1 s.

What's shared vs platform-specific

Roughly 97 % of the codebase is shared Dart. Platform-specific code is isolated behind abstract interfaces.

Shared (in lib/)

• All business logic
• All API integrations
• All UI widgets and screens
• All state management
• All caching and storage
• All price prediction / eco-score math
• All route search strategies
• All localisation (23 ARB files)

Platform-specific (behind abstractions)

Concern	Abstract interface	Android impl	Notes
Bluetooth	BluetoothFacade	PluginBluetoothFacade (flutter_blue_plus)	obd2_permissions.dart is platform-gated
Location	LocationProvider	GeolocatorLocationProvider	iOS impl would be identical via geolocator
Notifications	LocalNotificationService	FlutterLocalNotificationsService	Android 13+ needs POST_NOTIFICATIONS permission
Background	WorkManager	AndroidBackgroundPriceFetcher	iOS: BGTaskScheduler when porting
Secure storage	SecureStorage	FlutterSecureStorage (Keystore)	iOS: Keychain; Windows: DPAPI
Geocoding	GeocodingProvider	NativeGeocodingProvider + NominatimGeocodingProvider	Native falls through to Nominatim
Home-screen widget	widget_platform.dart (method channel)	Kotlin RemoteViews	iOS: WidgetKit when porting

Pure native only

• android/app/src/main/kotlin/.../TankstellenWidgetProvider.kt — the home widget. All state is passed from Dart via SharedPreferences bridging.
• android/app/build.gradle — signing, split-per-ABI, versioning (read from pubspec.yaml).
• AndroidManifest.xml — permissions (BLE split, no-foreground-service, neverForLocation).

How Flutter helps each platform

Android (shipping)

• APK + AAB built from CI, both in-repo scripts and the Play Console pipeline.
• Min SDK 24 (Android 7) — 99 %+ of active devices.
• Target SDK 36 — Android 15.
• Split per ABI — three APKs (armeabi-v7a, arm64-v8a, x86_64) keep install size ~20 MB each vs 60 MB fat AAB.

iOS (planned)

The code compiles on iOS today. What's missing for ship-readiness:

• BLE permissions on iOS plist (NSBluetoothAlwaysUsageDescription, etc.)
• Replace WorkManager with BGTaskScheduler
• Home-widget replacement with WidgetKit
• App Store review process for OBD2 read access (requires entitlements)
• CI runner for iOS (currently Linux only)

Desktop (not shipping)

• windows/, linux/, macos/ directories exist but aren't tested.
• OBD2 would need a USB-serial transport (the BLE abstraction still works via flutter_blue_plus desktop).
• The layout already adapts: NavigationRail on ≥600 dp, which is desktop-sized.

Web (dev only)

Used for quick UI review in the browser. Disabled in production because:

• Hive web is IndexedDB-backed — works, but data doesn't survive browser storage cleanup.
• Nominatim and OSM tiles have permissive CORS, but Tankerkoenig does not.
• No OBD2 (Web Bluetooth isn't universal enough).

Flutter versions

• Flutter 3.41.5 (stable channel, pinned in CI)
• Dart 3.11.3

Pinning avoids "works on my machine but CI fails" issues. Bumps happen via a dedicated chore/bump-flutter branch, tested against the full suite.

The "no Google dependency" rule

The privacy policy commits to no Google Play Services and no Firebase. Flutter plugins are vetted before adoption:

• ❌ Any plugin that requires com.google.gms:google-services
• ❌ Any plugin that transitively pulls Firebase
• ✅ flutter_blue_plus (BLE, MIT, no GMS)
• ✅ geolocator (location, MIT, no GMS when fused provider isn't mandatory)
• ✅ workmanager (background, MIT, pure WorkManager)

Transitive deps are audited via flutter pub deps --style=compact on every dependabot PR.

Related

• Project Structure — where each platform sits on disk
• OBD2 Implementation — example of the facade pattern for platform isolation