ViewModel and UDF

BookNest now looks like an app, but its logic lives in composables: the cart is a remembered list in BookNestNav, and the catalog is parsed in MainActivity. This section moves it into the architecture Google recommends: ViewModels that own screen state and logic, expose it as StateFlow and receive user actions as events, the shape of React 7,897 's useReducer and Redux 3,824 (UDF vs useReducer).

Subsections

• Logic Outside Composables
• ViewModel
• Exposing State with StateFlow
• collectAsStateWithLifecycle
• Unidirectional Data Flow
• One-Time Events
• BookNest's ViewModel Layer
• UDF vs useReducer