Gluestack UI v4 - Performance & Cross-Platform

This sub-skill focuses on performance optimization, cross-platform compatibility, and React Native best practices for gluestack-ui v4.

Rule 12: Cross-Platform Rendering (Native & Web)

Gluestack UI v4 components are designed to work seamlessly on both React Native (iOS/Android) and Web platforms. Always use Gluestack wrapper components instead of direct React Native imports to ensure cross-platform compatibility.

Critical Rule: Always Use Gluestack Wrappers

NEVER import components directly from react-native when a Gluestack wrapper exists. Gluestack wrappers handle platform-specific differences automatically.

Platform-Specific Component Mapping

React Native Import	Gluestack Wrapper	Notes
KeyboardAvoidingView from react-native	KeyboardAvoidingView from @/components/ui/keyboard-avoiding-view	Required for web compatibility
Platform from react-native	Use only when absolutely necessary	Prefer Gluestack's built-in platform handling
View, Text, etc.	Box, Text from @/components/ui/*	Always use Gluestack components

Correct Pattern: Cross-Platform Components

// ✅ CORRECT: Using Gluestack KeyboardAvoidingView wrapper
import { KeyboardAvoidingView } from '@/components/ui/keyboard-avoiding-view';
import { Platform } from 'react-native'; // Only when needed for platform-specific logic

<KeyboardAvoidingView
  behavior={Platform.OS === 'ios' ? 'padding' : 'height'}
  className="flex-1"
>
  <ScrollView>
    {/* Content */}
  </ScrollView>
</KeyboardAvoidingView>

Incorrect Pattern: Direct React Native Imports

// ❌ INCORRECT: Direct import from react-native
import { KeyboardAvoidingView, Platform } from 'react-native';

<KeyboardAvoidingView behavior={Platform.OS === 'ios' ? 'padding' : 'height'}>
  {/* This may not work correctly on web */}
</KeyboardAvoidingView>

Web-Specific Considerations

1. KeyboardAvoidingView: The Gluestack wrapper handles web gracefully (web doesn't need keyboard avoidance)
2. SafeAreaView: Works on both native and web (web treats it as a regular View)
3. ScrollView: Works identically on both platforms
4. Platform.select: Only use when absolutely necessary; prefer Gluestack's built-in handling

Testing Cross-Platform Compatibility

Always test components on both platforms:

1. Native: Run npm run ios or npm run android
2. Web: Run npm run web and verify in browser
3. Verify: Check that all components render correctly and interactions work on both platforms

Platform-Specific Code (When Necessary)

If you must use platform-specific code, use it sparingly and document why:

// Acceptable: Platform-specific behavior when Gluestack doesn't cover it
import { Platform } from 'react-native';

const keyboardBehavior = Platform.OS === 'ios' ? 'padding' : 'height';

<KeyboardAvoidingView behavior={keyboardBehavior} className="flex-1">
  {/* Content */}
</KeyboardAvoidingView>

Common Cross-Platform Issues to Avoid

1. Direct React Native imports - Always use Gluestack wrappers
2. Platform-specific styling without fallbacks - Ensure web has equivalent styles
3. Native-only APIs - Check if web alternatives exist
4. Missing web polyfills - Gluestack handles most of these automatically

Verification Checklist for Cross-Platform

• All components imported from @/components/ui/* wrappers
• No direct imports from react-native for wrapped components
• KeyboardAvoidingView uses Gluestack wrapper
• Tested on both native (iOS/Android) and web platforms
• All interactions work on both platforms
• Styling renders correctly on both platforms
• No platform-specific code without documentation

Rule 13: Performance & Best Practices

Follow these best practices to ensure optimal performance, type safety, and maintainability in React Native/Expo applications.

Use TypeScript

Define navigation and prop types for type safety. This catches errors at compile time and improves developer experience.

Correct Pattern

// ✅ CORRECT: Typed component props
interface LoginFormProps {
  readonly onSubmit: (email: string, password: string) => void;
  readonly isLoading?: boolean;
}

const LoginForm = ({ onSubmit, isLoading = false }: LoginFormProps) => {
  // Component implementation
};

// ✅ CORRECT: Typed navigation
import { useRouter } from 'expo-router';

const router = useRouter();
router.push('/login' as any); // Type-safe navigation

Incorrect Pattern

// ❌ INCORRECT: No type definitions
const LoginForm = ({ onSubmit, isLoading }) => {
  // No type safety
};

Memoize Components

Use React.memo and useCallback to prevent unnecessary rerenders, especially for expensive components or frequently re-rendered parent components.

Correct Pattern

// ✅ CORRECT: Memoized component
import React, { useCallback, useState } from 'react';

const ExpensiveComponent = React.memo(({ data, onUpdate }: Props) => {
  // Expensive rendering logic
});

const ParentComponent = () => {
  const [count, setCount] = useState(0);

  // Memoized callback prevents child rerenders
  const handleUpdate = useCallback((value: string) => {
    // Update logic
  }, []);

  return (
    <>
      <Button onPress={() => setCount(count + 1)}>
        <ButtonText>Count: {count}</ButtonText>
      </Button>
      <ExpensiveComponent data={data} onUpdate={handleUpdate} />
    </>
  );
};

When to Memoize

• Components that receive stable props but parent rerenders frequently
• Callbacks passed to child components
• Expensive computations (use useMemo)

Run Animations on UI Thread

Use Reanimated worklets for 60fps animations. This keeps animations smooth by running on the native UI thread instead of the JavaScript thread.

Correct Pattern

// ✅ CORRECT: Using Reanimated worklets
import { useSharedValue, withTiming } from 'react-native-reanimated';
import Animated from 'react-native-reanimated';

const AnimatedBox = Animated.createAnimatedComponent(Box);

const Component = () => {
  const translateX = useSharedValue(0);

  const handlePress = () => {
    // Animation runs on UI thread
    translateX.value = withTiming(100, { duration: 300 });
  };

  return (
    <AnimatedBox
      style={{
        transform: [{ translateX }],
      }}
    >
      <Pressable onPress={handlePress}>
        <Text>Animate</Text>
      </Pressable>
    </AnimatedBox>
  );
};

Incorrect Pattern

// ❌ INCORRECT: Using Animated API (runs on JS thread)
import { Animated } from 'react-native';

const Component = () => {
  const translateX = new Animated.Value(0);
  // This runs on JavaScript thread, can cause jank
};

Handle Safe Areas

Use SafeAreaView or useSafeAreaInsets to handle device notches, status bars, and home indicators properly.

Correct Pattern

// ✅ CORRECT: Using SafeAreaView
import { SafeAreaView } from '@/components/ui/safe-area-view';

const Screen = () => (
  <SafeAreaView className="flex-1 bg-background">
    <VStack className="p-4">
      {/* Content */}
    </VStack>
  </SafeAreaView>
);

// ✅ CORRECT: Using useSafeAreaInsets for custom layouts
import { useSafeAreaInsets } from 'react-native-safe-area-context';

const CustomLayout = () => {
  const insets = useSafeAreaInsets();

  return (
    <Box style={{ paddingTop: insets.top }}>
      {/* Content */}
    </Box>
  );
};

Test on Real Devices

Simulator/emulator performance differs from real devices. Always test on physical devices before releasing.

Testing Checklist

• Test on real iOS device (iPhone/iPad)
• Test on real Android device
• Test on different screen sizes
• Test with different OS versions
• Test performance under load
• Test with slow network conditions

Use FlatList for Lists

Never use ScrollView with map for long lists. FlatList provides virtualization, which only renders visible items.

Correct Pattern

// ✅ CORRECT: Using FlatList
import { FlatList } from '@/components/ui/flat-list';

const ItemList = ({ items }: { items: Item[] }) => (
  <FlatList
    data={items}
    renderItem={({ item }) => (
      <Box className="p-4 border-b border-border">
        <Text>{item.name}</Text>
      </Box>
    )}
    keyExtractor={(item) => item.id}
    ListEmptyComponent={<Text>No items found</Text>}
  />
);

Incorrect Pattern

// ❌ INCORRECT: Using ScrollView with map (no virtualization)
import { ScrollView } from '@/components/ui/scroll-view';

const ItemList = ({ items }: { items: Item[] }) => (
  <ScrollView>
    {items.map((item) => (
      <Box key={item.id} className="p-4">
        <Text>{item.name}</Text>
      </Box>
    ))}
  </ScrollView>
);

Why this is bad: All items are rendered at once, causing performance issues with long lists.

Platform-Specific Code

Use Platform.select for iOS/Android differences. This provides a clean, declarative way to handle platform-specific code.

Correct Pattern

// ✅ CORRECT: Using Platform.select
import { Platform } from 'react-native';

const styles = Platform.select({
  ios: {
    paddingTop: 20,
  },
  android: {
    paddingTop: 0,
  },
  default: {
    paddingTop: 0,
  },
});

<Box style={styles}>
  {/* Content */}
</Box>

// ✅ CORRECT: Platform.select for values
const keyboardBehavior = Platform.select({
  ios: 'padding',
  android: 'height',
  default: 'padding',
});

Incorrect Pattern

// ❌ INCORRECT: Using if/else for platform checks
import { Platform } from 'react-native';

let styles;
if (Platform.OS === 'ios') {
  styles = { paddingTop: 20 };
} else {
  styles = { paddingTop: 0 };
}

Best Practices Summary

Practice	Why It Matters	When to Use
TypeScript	Type safety, catch errors early	Always
React.memo	Prevent unnecessary rerenders	Components with stable props
useCallback	Stable function references	Callbacks passed to children
Reanimated worklets	60fps animations	All animations
SafeAreaView	Handle device notches/bars	All screens
FlatList	Virtualization for performance	Lists with 10+ items
Platform.select	Clean platform-specific code	iOS/Android differences
Real device testing	Accurate performance metrics	Before release

Performance Optimization Patterns

Memoized List Item

// ✅ CORRECT: Memoized list item component
interface ItemProps {
  readonly item: Item;
  readonly onPress: (id: string) => void;
}

const ListItem = React.memo(({ item, onPress }: ItemProps) => {
  const handlePress = useCallback(() => {
    onPress(item.id);
  }, [item.id, onPress]);

  return (
    <Pressable onPress={handlePress}>
      <Box className="p-4 border-b border-border">
        <Text>{item.name}</Text>
      </Box>
    </Pressable>
  );
});

// Parent component
const ItemList = ({ items }: { items: Item[] }) => {
  const handlePress = useCallback((id: string) => {
    // Handle press
  }, []);

  return (
    <FlatList
      data={items}
      renderItem={({ item }) => (
        <ListItem item={item} onPress={handlePress} />
      )}
      keyExtractor={(item) => item.id}
    />
  );
};

Animated Component

// ✅ CORRECT: Using Reanimated for smooth animations
import Animated, {
  useSharedValue,
  useAnimatedStyle,
  withSpring,
} from 'react-native-reanimated';

const AnimatedBox = Animated.createAnimatedComponent(Box);

const AnimatedCard = () => {
  const scale = useSharedValue(1);

  const animatedStyle = useAnimatedStyle(() => ({
    transform: [{ scale: scale.value }],
  }));

  const handlePress = () => {
    scale.value = withSpring(1.1);
  };

  return (
    <AnimatedBox style={animatedStyle} className="bg-card p-4 rounded-lg">
      <Pressable onPress={handlePress}>
        <Text>Press to animate</Text>
      </Pressable>
    </AnimatedBox>
  );
};

Safe Area Handling

// ✅ CORRECT: Proper safe area handling
import { SafeAreaView } from '@/components/ui/safe-area-view';
import { useSafeAreaInsets } from 'react-native-safe-area-context';

const Screen = () => {
  const insets = useSafeAreaInsets();

  return (
    <SafeAreaView className="flex-1 bg-background">
      <VStack className="flex-1">
        {/* Header */}
        <Box className="p-4 border-b border-border">
          <Heading size="xl">Title</Heading>
        </Box>

        {/* Content */}
        <ScrollView className="flex-1">
          {/* Content */}
        </ScrollView>

        {/* Footer with safe bottom padding */}
        <Box
          style={{ paddingBottom: insets.bottom }}
          className="p-4 border-t border-border"
        >
          <Button>
            <ButtonText>Submit</ButtonText>
          </Button>
        </Box>
      </VStack>
    </SafeAreaView>
  );
};

Performance Checklist

• TypeScript types defined for all components and props
• Expensive components wrapped with React.memo
• Callbacks memoized with useCallback
• Animations use Reanimated worklets
• Safe areas handled with SafeAreaView or useSafeAreaInsets
• Long lists use FlatList instead of ScrollView + map
• Platform-specific code uses Platform.select
• Tested on real devices (not just simulators)
• Performance profiled and optimized
• Cross-platform compatibility verified (native + web)

Common Performance Pitfalls

❌ Don't: Use ScrollView for Long Lists

// ❌ INCORRECT: No virtualization
<ScrollView>
  {items.map(item => <Item key={item.id} {...item} />)}
</ScrollView>

// ✅ CORRECT: Use FlatList
<FlatList
  data={items}
  renderItem={({ item }) => <Item {...item} />}
  keyExtractor={(item) => item.id}
/>

❌ Don't: Create Callbacks Without useCallback

// ❌ INCORRECT: New function on every render
<Button onPress={() => handlePress(id)}>
  <ButtonText>Press</ButtonText>
</Button>

// ✅ CORRECT: Memoized callback
const memoizedPress = useCallback(() => {
  handlePress(id);
}, [id, handlePress]);

<Button onPress={memoizedPress}>
  <ButtonText>Press</ButtonText>
</Button>

❌ Don't: Use Animated API for Complex Animations

// ❌ INCORRECT: Runs on JavaScript thread
import { Animated } from 'react-native';
const animValue = new Animated.Value(0);

// ✅ CORRECT: Use Reanimated (runs on UI thread)
import { useSharedValue } from 'react-native-reanimated';
const animValue = useSharedValue(0);

Reference

• Reanimated Documentation: https://docs.swmansion.com/react-native-reanimated/
• React Native Performance: https://reactnative.dev/docs/performance
• Expo Router: https://docs.expo.dev/router/introduction/