igorescodro/write-viewmodel

Write ViewModel

Overview

ViewModels in Alkaa bridge domain use cases and Compose UI via cold flows and sealed state classes. They contain no business logic — only orchestration, mapping, and scope management.

Structure

1. Sealed State Class — data object for stateless states, data class for states with data, ImmutableList for list payloads → see references/CODE_PATTERNS.md
2. Flow Exposure — Cold Flow<ViewState> by default; hot StateFlow only when multiple collectors share the same stream → see references/CODE_PATTERNS.md
3. Use Case Injection — Inject use cases as constructor parameters; never repositories or other ViewModels → see references/CODE_PATTERNS.md
4. Coroutine Scope — applicationScope for DB mutations that survive ViewModel destruction; viewModelScope for UI-bound work → see references/CODE_PATTERNS.md
5. Mappers — Dedicated mapper class injected as constructor param; never map inline → see references/CODE_PATTERNS.md

For unit test setup and fake patterns → see references/CODE_PATTERNS.md and the write-unit-tests skill.

Scope Rules

| Situation | Scope | |-----------|-------| | DB insert / update / delete | applicationScope.launch { } | | Network call that should persist | applicationScope.launch { } | | Debounced UI updates | viewModelScope | | Short-lived UI-bound work | viewModelScope |

Common Mistakes

| Mistake | Fix | |---------|-----| | Calling repository directly | Wrap in a use case first | | Exposing StateFlow for a screen-scoped stream | Return cold Flow<ViewState> | | Mapping models inline in ViewModel | Create a XxxMapper class | | Using viewModelScope for DB writes | Use applicationScope.launch { } | | Depending on another ViewModel | Extract shared logic into a use case | | Testing with mocks | Write a XxxFake that implements the use case interface |

Related Skills

• Fake patterns and test structure → use write-unit-tests skill
• Composable and screen wiring → use write-composable skill