Building Cross-Platform Apps with Flutter: What I Learned at My First Internship

My internship at Simba Developers was my first experience building a production mobile app. Flutter's promise of "write once, run anywhere" sounds great in theory — here's what it actually looks like in practice.

The Challenge

Simba Developers needed a mobile application that worked on both iOS and Android. The team was small — just three developers — and maintaining two separate native codebases wasn't feasible. The app needed real-time data sync, push notifications, deep linking, and smooth animations. Performance needed to feel native, not like a web view wrapped in a container.

The Goal

As the mobile development intern, I was responsible for building the cross-platform app using Flutter and Dart, integrating Firebase for authentication and real-time database, implementing push notifications, and ensuring the UI rendered smoothly on both platforms with native-feeling performance.

The Approach

I chose Provider for state management after evaluating Bloc and Riverpod — Provider offered the best balance of simplicity and power for our use case. For real-time features, Cloud Firestore's snapshot listeners gave us live data synchronization without building a custom WebSocket infrastructure. The push notification implementation required platform-specific setup (APNs for iOS, FCM for Android), but Flutter's platform channels handled the abstraction cleanly. Deep linking was the trickiest part — I used the uni_links package to handle both universal links (iOS) and app links (Android) with a unified routing system.

The biggest performance optimization came from widget tree management. Flutter rebuilds entire widget subtrees when state changes, and naively structured state could cause the entire screen to rebuild on every data update. I used const constructors aggressively, broke large widgets into smaller stateless components, and moved state subscriptions as low in the tree as possible.

The Impact

The app achieved a 44% improvement in UI rendering performance compared to the team's initial prototype, supported 1,000+ concurrent users with real-time sync, and push notifications with deep linking increased user engagement by 28%. The single codebase meant our three-person team could iterate faster than a larger team maintaining separate native apps.

Key Takeaways

Flutter genuinely delivers on cross-platform performance when you understand its rendering model. State management choice matters enormously — pick the simplest tool that handles your complexity. Widget tree structure has a direct, measurable impact on performance. And platform-specific features (notifications, deep links) still require understanding native iOS and Android concepts even in a cross-platform framework.

Questions? kanade.pra@northeastern.edu