Sub Tracker
A cross-platform Flutter mobile application designed to track recurring subscriptions, eliminate unwanted auto-debits, and manage expense budgets with offline local data caching and REST API synchronization.
Project Overview
Sub Tracker is a Flutter mobile application engineered to give users full control over their recurring digital subscriptions, streaming memberships, and software licenses.
Built with Flutter and Dart, the app features robust local data persistence for instant offline access, synchronized with REST APIs for multi-device cloud backup. It delivers intelligent background renewal notifications, category breakdown charts, and budget analytics to eliminate forgotten auto-debits.
My Engineering Role
Lead Flutter Mobile Developer responsible for mobile UI architecture, local data storage, REST API client integration, state management, and push notification alert scheduling.
The Challenge
Ensuring instant app launch times and reliable offline availability while accurately calculating irregular billing cadences, currency conversions, and scheduling background renewal alarms across iOS and Android battery-optimization constraints.
The Solution
Implemented Flutter Clean Architecture with offline-first local data persistence, a resilient REST API repository with token interceptors, and local notification scheduling that triggers regardless of internet connection status.
High-Level Architecture
- Flutter cross-platform client with Clean Architecture separating domain, data, and presentation layers.
- Fast local database storage for offline-first persistence and instant startup without network dependency.
- RESTful API client with HTTP interceptors, automated token refresh, and normalized JSON error contracts.
- Background notification scheduling engine delivering proactive renewal alerts (1 day, 3 days, 1 week before auto-debit).
Key Features & Workflows
- Active subscription catalog with recurrence cadence modeling (monthly, quarterly, annual, custom intervals)
- High-speed local database persistence guaranteeing complete offline functionality
- REST API synchronization for seamless multi-device cloud backup and data restoration
- Proactive renewal reminder alerts with custom notification lead times
- Visual expenditure charts categorized by Entertainment, Work, Utilities, and Fitness
Technical Challenges Overcome
- Architecting reliable offline-first local data caching with seamless REST API conflict resolution
- Accurate billing cycle math across leap years, irregular monthly durations, and custom billing dates
- Ensuring dependable local push notifications trigger reliably on Android Doze mode and iOS background state
Production Results & Impact
- Smooth 60 FPS mobile user interface with sub-second cold boot powered by local data caching.
- Publicly linked video demonstration showcasing mobile workflows, local storage, and alert triggers.
- Prevented unwanted auto-debits and reduced recurring software expenditure for active users.
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