Building Celebration Magic: Inside LINE's Android Event System
Have you ever opened an app on your birthday and felt a little spark of joy when it suddenly burst into celebration? That moment of happiness is exactly what we wanted to create at LINE, and as an Android engineer at LY Corporation, I had the chance to work on the system that makes it happen.
Recently, I wrote a detailed post about one of my favorite projects: the Home tab event system that powers birthday and holiday celebrations for millions of LINE app users. It was one of those rare engineering challenges where technical problems meet real human feelings.
The Challenge: Making Magic Feel Effortless
When I first joined this project, I thought we were just building some animation effects. How hard could it be, right? Well, it turned out that creating those perfect celebration moments means solving some really tough engineering problems:
- Perfect timing that works when the app restarts and the phone reboots
- Smart resource handling for millions of daily users
- Dealing with problems like network failures and user setting changes
- Managing two celebration types: personal moments (birthdays) and cultural events (holidays)
The more I worked on this project, the more I realized that what looks like simple magic to users needs some serious engineering work underneath.
The Architecture: Four Phases of Celebration
What I found interesting about this project was how we turned a messy user experience into a clear, step-by-step setup. It reminded me of planning a surprise party—everything has to work together perfectly, but the guest of honor should never see the preparation:
Phase 1: Event Discovery
We start with smart detection and a 5-day preparation buffer—because I learned that timing is absolutely everything in celebrations. Nobody wants a late birthday wish!
Phase 2: Resource Acquisition
This became our three-step process to ensure all assets are downloaded, validated, and ready before showtime. I’ve been burned by missing resources before, so we made this bulletproof.
Phase 3: Show Time
The magic moment where Kotlin Flow, Room database, and careful state management all come together to orchestrate seamless visual transitions. This is where months of work pay off in seconds of user delight.
Phase 4: Clean Up
Intelligent resource management that keeps the app performant while handling recurring events. Because nobody likes an app that gets slower after every celebration.
Technical Details That Made It Work
Looking back, I’m pretty proud of how we leveraged Android’s native toolkit effectively. Sometimes the best solutions are the ones that work with the platform, not against it:
- Kotlin Flow for reactive UI updates that respond instantly to celebration triggers
- Room database with reactive queries for reliable local storage
- WorkManager for precise scheduling that survives system restarts
- Strategic separation of concerns between event discovery and resource management
Each of these choices was on purpose. I’ve seen too many projects fail because they tried to build everything from scratch when the platform already had good solutions.
Why This Matters Beyond LINE
While this system is made for LINE’s celebrations, working on it taught me that the patterns and Android ways we developed can be used in many places. If you’re building:
- Complex UI systems
- Resource-intensive features with precise timing
- Multi-phase workflows with error recovery
- Reactive UI systems at scale
The principles we developed—early preparation, clear phase separation, user-centric timing decisions—can definitely help you approach similar challenges. I wish I had known these patterns earlier in my career.
Read the Full Technical Deep Dive
I’ve written the complete technical breakdown on our company engineering blog. If you’re interested in the detailed info, it covers:
- Detailed code examples with WorkManager scheduling
- State management patterns for complex UI transitions
- Resource lifecycle optimization strategies
- Error handling approaches for mobile environments
- Performance considerations for millions of users
Working on this project reminded me why I love being an engineer. The best solutions don’t just solve technical problems—they create real moments of human connection and joy. Sometimes the most meaningful code is the code that makes people smile when they least expect it. I hope you find the article helpful, and maybe it will inspire you to create your own moments of magic in your apps!