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How to fix slow performance with 100+ items React Native flatlist?

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When dealing with a large number of items in a React Native FlatList, performance can become an issue, especially on lower-end devices. Here are some strategies to improve the performance of a FlatList with 100+ items:

1. Use getItemLayout

Provide the getItemLayout prop to the FlatList component. This prop tells the FlatList how to calculate the height of items before they are rendered, which can improve scroll performance.

2. Virtualization

By default, FlatList virtualizes rendering, meaning it only renders items that are currently visible on the screen. Ensure that your data source is efficiently structured, and consider implementing getItemLayout or initialNumToRender to optimize the number of items rendered initially.

3. Optimize Render Item

Make sure the renderItem function is optimized. Avoid complex calculations or rendering large numbers of components within each item.

4. Use PureComponent or memo

If your item component doesn’t rely on props that change frequently, consider using PureComponent (class component) or React.memo (functional component) to prevent unnecessary re-renders.

5. KeyExtractor

Provide a unique keyExtractor function to the FlatList. This helps React Native optimize rendering by identifying each item uniquely.

6. Windowed Rendering

Implement a windowed rendering technique where only items within a certain window around the viewport are rendered. This reduces the number of items rendered at any given time, improving performance.

7. Data Pagination

If possible, paginate your data so that only a subset of items is loaded initially. Load additional items as the user scrolls.

8. Use PureComponent for renderItem

If you’re using class components, make sure your renderItem component is a PureComponent to prevent unnecessary re-renders.

9. Avoid Complex Operations in Render:

Avoid complex operations, calculations, or heavy computations within the renderItem function. Pre-calculate data or perform heavy operations outside the render function.

10. Avoid Inline Functions

Avoid defining inline functions within renderItem, as this can cause unnecessary re-renders.

Instead, define functions outside of the component or memoize them using useMemo or useCallback.

By implementing these strategies, you can significantly improve the performance of a FlatList with 100+ items in React Native.

By John Au-Yeung

Web developer specializing in React, Vue, and front end development.

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