One Big Mistake in Early Android Apps: UI Widgets as State Source

Why Early Android Apps Feel Fragile

In fast tutorial-style Android projects, screen logic often gets embedded directly in Activities. It works during demos but breaks under lifecycle and rotation events.

Step 1: Move state out of Activity fields

data class QuizState(
    val index: Int = 0,
    val score: Int = 0,
    val finished: Boolean = false
)

Step 2: Handle events through a reducer

fun reduce(state: QuizState, correct: Boolean): QuizState {
    val nextScore = if (correct) state.score + 1 else state.score
    val nextIndex = state.index + 1
    return state.copy(index = nextIndex, score = nextScore, finished = nextIndex >= 10)
}

Step 3: Render UI from immutable snapshot

Every render cycle should read from one state object, not multiple mutable globals.

Pitfalls

• State reset on rotation because values live only in Activity fields.
• UI widgets used as the source of truth.
• No event tests for end-of-quiz transitions.

Verification

• Progress survives lifecycle recreation events.
• Reducer tests cover all event branches.
• Final score remains stable across orientation changes.