FlatList Data, renderItem, and keyExtractor
Pass an array to FlatList's data prop, implement renderItem to return a styled row component, and provide a keyExtractor for stable list identity.
FlatList Data, renderItem, and keyExtractor is a free React Native Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the React Native Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Why FlatList Instead of ScrollView?
ScrollView renders all its children at once, which becomes slow when displaying hundreds of items. FlatList virtualizes the list — it only renders the items currently visible on screen plus a small buffer, dramatically reducing memory usage and improving scroll performance for large datasets.
The data Prop
Pass your array of items to the data prop. FlatList iterates over this array and calls renderItem for each element. The array can contain any kind of JavaScript objects. Changes to the data array trigger a re-render of affected list items.
const DATA = [
{ id: '1', name: 'Alice' },
{ id: '2', name: 'Bob' },
{ id: '3', name: 'Carol' },
];
<FlatList data={DATA} ... />The renderItem Prop
The renderItem prop is a function that receives an object with an item property (the current array element) and must return a React element. This is where you define how each row looks. Keep it as a stable reference using useCallback to avoid unnecessary re-renders.
const renderItem = ({ item }) => (
<View style={styles.row}>
<Text>{item.name}</Text>
</View>
);
<FlatList
data={DATA}
renderItem={renderItem}
/>The keyExtractor Prop
keyExtractor tells FlatList how to extract a unique string key from each item. React uses these keys to track which items changed during re-renders. Without a proper key extractor FlatList falls back to the array index, which can cause subtle bugs during data mutations.
<FlatList
data={DATA}
renderItem={renderItem}
keyExtractor={(item) => item.id}
/>A Complete FlatList Example
Combining data, renderItem, and keyExtractor gives you a fully functional, scrollable, virtualized list. You can style the rows inside renderItem just like any other component. FlatList automatically handles scroll and touch events.
import { FlatList, View, Text, StyleSheet } from 'react-native';
const DATA = [
{ id: '1', title: 'First Item' },
{ id: '2', title: 'Second Item' },
{ id: '3', title: 'Third Item' },
];
export default function App() {
return (
<FlatList
data={DATA}
keyExtractor={(item) => item.id}
renderItem={({ item }) => (
<View style={styles.item}>
<Text>{item.title}</Text>
</View>
)}
/>
);
}
const styles = StyleSheet.create({
item: { padding: 16, borderBottomWidth: 1, borderColor: '#eee' },
});Adding a List Header and Footer
Use ListHeaderComponent to render content above the list (such as a search bar or page title) and ListFooterComponent for content below (such as a loading spinner when fetching more data). These components scroll with the list, unlike a view placed outside FlatList.
<FlatList
data={DATA}
renderItem={renderItem}
keyExtractor={(item) => item.id}
ListHeaderComponent={() => <Text style={styles.header}>Users</Text>}
ListFooterComponent={() => <ActivityIndicator />}
/>Empty List with ListEmptyComponent
When the data array is empty, FlatList renders nothing by default. Provide a ListEmptyComponent to display a placeholder message or illustration when there are no items. This is much cleaner than wrapping FlatList in a conditional.
<FlatList
data={filteredData}
renderItem={renderItem}
keyExtractor={(item) => item.id}
ListEmptyComponent={() => (
<Text style={styles.empty}>No results found</Text>
)}
/>Item Separators with ItemSeparatorComponent
Instead of adding border styles directly to item rows, use ItemSeparatorComponent to render a separator between items. React Native only renders the separator between items, not before the first or after the last, which avoids double borders at the edges.
const Separator = () => (
<View style={{ height: 1, backgroundColor: '#eee' }} />
);
<FlatList
data={DATA}
renderItem={renderItem}
keyExtractor={(item) => item.id}
ItemSeparatorComponent={Separator}
/>Horizontal FlatList
Set the horizontal prop to true to render a horizontally scrolling list. This is useful for carousels, category chips, or story rows. The showsHorizontalScrollIndicator prop can hide the scroll bar for a cleaner look.
<FlatList
horizontal
showsHorizontalScrollIndicator={false}
data={categories}
renderItem={({ item }) => (
<View style={styles.chip}>
<Text>{item.label}</Text>
</View>
)}
keyExtractor={(item) => item.id}
/>Scrolling to an Index Programmatically
Use the ref on FlatList and call flatListRef.current.scrollToIndex({ index, animated: true }) to jump to a specific item. You can also use scrollToOffset for pixel-level control or scrollToEnd to scroll to the bottom of the list.
const flatListRef = useRef(null);
const scrollToTop = () => {
flatListRef.current.scrollToIndex({ index: 0, animated: true });
};
<FlatList ref={flatListRef} data={DATA} renderItem={renderItem} />Avoiding Common FlatList Mistakes
Avoid defining renderItem as an anonymous arrow function directly in JSX (renderItem={() => ...}). This creates a new function reference on every render, causing every row to re-render unnecessarily. Define it outside the JSX or memoize it with useCallback. Also never use an array index as the key — always use a stable unique ID.
// Bad: anonymous function in JSX
<FlatList renderItem={({ item }) => <Row item={item} />} />
// Good: stable reference
const renderItem = useCallback(({ item }) => <Row item={item} />, []);
<FlatList renderItem={renderItem} />Quick Check
Test your understanding of FlatList data, renderItem, and keyExtractor from this lesson.
Lesson Recap
In this lesson you learned: FlatList virtualizes large lists by only rendering visible items, renderItem defines the appearance of each row, and keyExtractor provides stable unique keys for efficient React reconciliation. Next up we explore pull-to-refresh and infinite scroll with load more.
Frequently asked questions
Is the “FlatList Data, renderItem, and keyExtractor” lesson free?
Yes — the full text of “FlatList Data, renderItem, and keyExtractor” is free to read here on the web, and the React Native Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the React Native Academy course, upgrade to CoddyKit PRO.
What will I learn in “FlatList Data, renderItem, and keyExtractor”?
Pass an array to FlatList's data prop, implement renderItem to return a styled row component, and provide a keyExtractor for stable list identity. You practise React Native Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start React Native Academy?
No prior experience is required. React Native Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “FlatList Data, renderItem, and keyExtractor” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this React Native Academy lesson?
Yes. Every React Native Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- FlatList Data, renderItem, and keyExtractor
- Pull-to-Refresh and Load More
- SectionList with Headers
- Building a Contacts List App