Context

Architecture choices directly affect testability, maintainability, and UI complexity in an iOS codebase such as the American Express Global Business Travel mobile app.

Question

Explain MVC and MVVM in the context of iOS development. Your answer should cover:

1. The role and responsibility of each layer in both patterns
2. How data flows between UI, business logic, and models
3. The trade-offs in testability, scalability, and developer ergonomics
4. When you would choose MVC versus MVVM for a feature in the American Express Global Business Travel app

Scope Guidance

Keep the discussion focused on practical iOS engineering. The interviewer expects you to compare the two patterns clearly, mention common pitfalls such as “Massive View Controller,” and explain how your choice changes for simple screens versus state-heavy, data-driven screens.