Question 323002 in React native Question posted in
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Optimizing React Native App for Unnecessary Re-renders

I am currently working on a React Native app, and I’ve encountered performance issues related to unnecessary re-renders, especially when changing the state in the parent component. I have taken steps to optimize the code, such as using React.memo for memoization, but the problem persists.

In the UserProfileScreen component, I have a FlatList that renders a list of posts based on the active state. The child component RenderItem is memoized using React.memo, but changing the state in the parent component triggers re-renders for all child components, causing a noticeable slowdown in the app.

I’ve considered using useMemo for memoizing values that don’t depend on state changes and useCallback for event handlers, but I’m still facing performance issues.

I’m seeking advice on further optimizations or alternative approaches to prevent unnecessary re-renders and improve the overall performance of my React Native app.

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2

Answers


  1. 0

    There are various techniques you can use to minimize unnecessary re-renders. Here are some tips and alternative approaches:

    Avoid Inline Functions in Render:
    Ensure that any functions passed as props to child components are not created inline within the render method. Inline functions can cause re-renders because a new reference is created on each render. Use useCallback to memoize functions.

    const handleItemClick = useCallback(() => {
 // your logic
 }, [/* dependencies */]);

<RenderItem onItemClick={handleItemClick} />

    Optimize FlatList with PureComponent:
    You can try using the PureComponent for your RenderItem component instead of React.memo. PureComponent performs a shallow comparison of props and state, potentially reducing unnecessary re-renders.

      class RenderItem extends React.PureComponent {
  // component logic
  }

    Memoize Expensive Computations with useMemo:
    Use useMemo to memoize values that are computationally expensive and do not depend on state changes. This can prevent unnecessary calculations on each render.

        const expensiveValue = useMemo(() => computeExpensiveValue(), [/* 
dependencies */]);

    Avoid Passing Functions as Props:
    If your child components don’t need to trigger state changes in the parent, consider whether you can avoid passing functions as props. If the functions don’t change, it might reduce re-renders.

    Check Dependencies in useEffect:
    If you’re using useEffect, make sure to carefully list dependencies. If any dependency changes frequently and isn’t needed inside the effect, consider moving it inside the callback or using useCallback to memoize the callback.

    Use VirtualizedLists for Large Data Sets:
    If you’re dealing with a large number of items in your FlatList, consider using VirtualizedLists such as FlatList or SectionList, as they are optimized for large datasets.

    Redux or Context API:
    If your state management becomes complex, consider using a state management library like Redux or React Context API. These tools can provide more control over when and how components re-render.

    Profile and Optimize:
    Use the React DevTools Profiler to identify performance bottlenecks. Optimize the components that consume the most resources first.

    Consider PureComponent for the Parent:
    If the parent component frequently re-renders unnecessarily, you might consider using PureComponent for the parent as well

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  2. 0

    Since you didn’t post any code and it seems your question is more specific to a ‘FlatList’ re-rendering here are my stabs at potential problems:

    1. Make sure you are using a key prop on the list item so that the list can try to avoid renders. You can use keyExtractor if that is easier. https://reactnative.dev/docs/flatlist#keyextractor
    2. Check all props going into that list item for changes. That includes any state passed in and any functions or anything else.
    3. Are you using a context inside of the list item? That could be causing the re-render of every item. https://react.dev/reference/react/useContext

    One of the things I have used to figure out what is causing re-renders is a useEffect for each prop with a console log in the dependency array. Its powerful because it will log every time that dependency changes so you can check to see if the slow down is because your list isn’t just rendering the whole thing again but if its re-rendering 2+ times before it settles back down. https://react.dev/reference/react/useEffect

    Maybe you are expecting every item to re-render on the state change so I might be off on what you are expecting if that is the case you might want to adjust the FlatList props for performance such as "initialNumToRender", "removeClippedSubview", and "getItemLayout". https://reactnative.dev/docs/flatlist#initialnumtorender

    Hope this helps. Good Luck!

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