dev.cds-mobile

---
name: "dev.cds-mobile"
description: "USE THIS when asked to work on a new or existing (MOBILE) CDS React component in packages/mobile"
license: "Apache-2.0"
---

<!-- TODO: nested AGENTS.md files should work but they seem a little flaky at the moment. Intelligent mdc files are working better -->

# CDS Mobile Package Guidelines

Mobile-specific patterns for `@coinbase/cds-mobile`.

## Component Config Adoption (Mobile)

Use this guidance when adding `ComponentConfigProvider` defaults for the specific component you are editing.

### Required implementation pattern

1. Register the component in `packages/mobile/src/core/componentConfig.ts` using its `*BaseProps`:

```ts
import type { MyComponentBaseProps } from '../category/MyComponent';

export type ComponentConfig = {
  MyComponent?: ConfigResolver<MyComponentBaseProps>;
};
```

1. Adopt `useComponentConfig` in the component and destructure from merged props:

```tsx
import { useComponentConfig } from '../hooks/useComponentConfig';

export const MyComponent = memo((_props: MyComponentProps) => {
  const mergedProps = useComponentConfig('MyComponent', _props);
  const { style, ...props } = mergedProps;

  return <Pressable style={style} {...props} />;
});
```

### Rules to preserve behavior

- Provider config supplies defaults only; local props must continue to win.
- Use `_props` as the input variable and `mergedProps` as the configured output.
- Type resolver entries with `*BaseProps` (not full `*Props`).
- Keep scope to prop-level theming defaults; do not alter component behavior or control flow.
- When practical during the same change, prefer arrow-function component declarations.

## Styling with StyleSheet

Use `StyleSheet.create` for static styles and `useTheme()` for dynamic values:

```tsx
import { StyleSheet, type StyleProp, type ViewStyle } from 'react-native';

const styles = StyleSheet.create({
  container: { position: 'relative', width: '100%' },
});

// Dynamic styles via theme hook
const theme = useTheme();
const dynamicStyle = {
  backgroundColor: theme.color.bgPrimary,
  padding: theme.space[2],
};

<View style={[styles.container, dynamicStyle, style]} />;
```

### Inline styles

- Mobile components should all expose a `style` and `styles` object props for overriding default styles.
- As styling is a concern of that specific component, the `style` and `styles` props should never be on the `*BaseProps` type.
- `styles` can be used for granular overrides on child elements within the component.
- **Always** merge styles into a react-native style array with `useMemo` in the correct order (default styles => `style` prop => `styles[ELEMENT_NAME]` prop).

**Example:**

```tsx
type ComponentProps = ComponentBaseProps & {
  style?: StyleProp<ViewStyle>;
  styles?: {
    root?: StyleProp<ViewStyle>;
    label?: StyleProp<TextStyle>;
  };
};

const theme = useTheme();
const containerStyles = useMemo(
  () => [
    { backgroundColor: theme.color.bgPrimary }, // default styles
    style, // from props
    styles.root, // from props
  ],
  [theme.color.bgPrimary, animatedStyles, style]
);

// Apply to component
<Box style={containerStyles}>
```

## Animation

### React Native Reanimated

```tsx
import Animated, { useAnimatedStyle, useSharedValue, withTiming } from 'react-native-reanimated';

const opacity = useSharedValue(0);
const animatedStyle = useAnimatedStyle(() => ({
  opacity: opacity.value,
  transform: [{ translateY: withTiming(opacity.value * -8) }],
}));

<Animated.View style={animatedStyle} />;
```

We DO NOT use React-Spring anymore for animations on mobile.

## Gesture Handling

Use `react-native-gesture-handler`:

```tsx
import { Gesture, GestureDetector } from 'react-native-gesture-handler';

const panGesture = useMemo(
  () =>
    Gesture.Pan()
      .onStart(() => {
        /* ... */
      })
      .onUpdate(({ translationX }) => {
        /* ... */
      })
      .onEnd(({ translationX, velocityX }) => {
        /* ... */
      })
      .withTestId(testID)
      .runOnJS(true),
  [dependencies],
);

<GestureDetector gesture={panGesture}>
  <Animated.View>{/* ... */}</Animated.View>
</GestureDetector>;
```

## Layout Measurement

Use `onLayout` callback instead of ResizeObserver:

```tsx
const [size, onLayout] = useLayout();
<View onLayout={onLayout} />

// Or inline
<View onLayout={(e) => setHeight(e.nativeEvent.layout.height)} />
```

## Accessibility

- Use appropriate accessibilityLabel, accessibilityHint, and accessibilityRole, accessibilityState props
- Support screen readers (VoiceOver and TalkBack)
- Ensure touch targets meet minimum size requirements (44x44 points)

**Example:** Use React Native accessibility props:

```tsx
<View
  accessible
  accessibilityRole="adjustable"
  accessibilityLabel="Product carousel"
  accessibilityLiveRegion="polite"
>
  <Pressable
    accessibilityState={{ selected: isActive, disabled }}
    accessibilityActions={[{ name: 'activate' }]}
    onAccessibilityAction={handleAccessibilityAction}
  />
</View>
```

### Screen Reader Content

```tsx
// Hide visual content from screen readers
<View accessibilityElementsHidden importantForAccessibility="no-hide-descendants">
  {/* Animated/visual content */}
</View>

// Provide accessible alternative
<Text
  importantForAccessibility="yes"
  accessibilityLiveRegion="polite"
  style={{ color: 'transparent', position: 'absolute' }}
>
  {accessibleLabel}
</Text>
```

## Reference Components

- **SlideButton**: gesture handling, spring animations, accessibility actions
- **RollingNumber**: Reanimated, measurement patterns, screen reader content
- **Select** (alpha/): controlled/uncontrolled, Drawer integration
- **Stepper**: direction-based defaults, shared logic from cds-common
- **Tour**: animations, complexity
- **DatePicker**: complexity