Harmony Arkts

# HarmonyOS ArkTS Rules

## Component Structure

- Use `@Component` for component definitions and PascalCase for component structs.
- Keep state declarations near the top of the component.
- Group lifecycle hooks before `build()`.
- Place `build()` last and keep it focused on UI composition.
- Extract complex UI into smaller components.

## State and Data Flow

- Use `@State` for component-owned state.
- Use `@Prop` for parent-to-child data.
- Use `@Link` only for intentional two-way binding.
- Keep derived values in methods or computed helpers rather than duplicating state.
- Avoid broad global state unless the project has an established app-state pattern.

## Layout and Styling

- Use `Column`, `Row`, `Stack`, `List`, and other ArkUI primitives intentionally.
- Keep layout properties such as width, height, alignment, and layout weight grouped before visual properties.
- Use object notation for margin and padding when sides differ.
- Use logical pixels consistently.
- Use percentage strings for relative sizes.
- Keep reusable spacing, colors, and typography in resources when the project supports it.

## Events and Lifecycle

- Use arrow functions for event handlers.
- Keep event handlers short and delegate complex logic to methods.
- Handle async failures explicitly and surface user-facing errors where appropriate.
- Use lifecycle hooks for setup and teardown that genuinely depends on component lifecycle.

## Resources and Accessibility

- Use `$r()` for app resources.
- Group resource references consistently.
- Add descriptive labels and focus handling for interactive elements.
- Maintain color contrast and touch target size.
- Test on representative device sizes and orientations.

## Common Mistakes

- Do not bury business logic in `build()`.
- Do not use two-way binding when one-way props are enough.
- Do not hardcode repeated strings, colors, and dimensions that belong in resources.
- Do not leave debug `console.log` calls in production code.