Interview Scenarios

Real-Time Chat

Building a chat app is a common interview scenario that tests your understanding of real-time systems, state management, and offline capabilities.

Prompt & Requirements

"Design a chat application that supports:

  • Real-time messaging between users
  • Offline message queue
  • Read receipts
  • Message history with pagination
  • Push notifications
Focus on the iOS client architecture and key technical decisions."

Key Technical Themes

Concurrency

  • WebSocket handling on background threads
  • Message processing queue
  • UI updates on main thread
  • Handling race conditions with message ordering

Local Persistence

  • Core Data vs. SQLite vs. Realm
  • Message schema design
  • Offline queue management
  • Sync conflict resolution

Common Pitfall

Don't jump straight to WebSocket implementation details. Start with high-level architecture and data flow. Interviewers want to see your system design thinking first.

Example Interview Questions

"How do you handle offline message sending?"

Key points to cover:

  • Local queue with pending messages table
  • Optimistic UI updates
  • Background retry mechanism
  • Conflict resolution on reconnection

"How would you scale to thousands of messages per second?"

Key points to cover:

  • Message batching and compression
  • Efficient pagination and caching
  • Background message cleanup
  • Memory management strategies