How to Manage Complex UI State in Jetpack Compose Using ViewModel and StateFlow

Android developers building screens with Jetpack Compose often struggle with scattered state variables, unnecessary recompositions, and state loss during configuration changes like screen rotation. The Unidirectional Data Flow (UDF) pattern addresses this by consolidating all screen state into a single immutable data class exposed via a StateFlow inside a ViewModel. In this approach, state flows down to the UI while user events flow back up to the ViewModel, making screens more predictable and easier to test. A real-world map-based routing screen is used to demonstrate how to model, update, and consume UI state using this architecture. The pattern relies on Kotlin fundamentals such as data classes and coroutines, along with Jetpack Compose basics, making it accessible to developers with intermediate Android experience.