DEV Community


Posted on

What is "VirtualizedLists should never be nested inside plain ScrollViews" in React Native?

What is VirtualizedLists Error?

In React Native, when you encounter a "VirtualizedLists should never be nested" error while trying to wrap a FlatList inside a ScrollView, it means you are trying to nest multiple virtualized lists within each other, which is not supported by the framework.

Virtualized lists like FlatList and SectionList are optimized for rendering long lists efficiently by rendering only the visible items on the screen. Nesting them within a ScrollView can lead to conflicts in managing the scroll behavior, as both the ScrollView and the inner FlatList are trying to control the scrolling.

How to overcome this issue?

Use a Single Virtualized List: If your goal is to display a list of items, you can often achieve the desired layout and functionality using a single FlatList or SectionList without the need for a ScrollView. You can style and customize the list to have headers, footers, or other elements as needed.

Use a Header Component: If you need to include elements above the FlatList, you can add them as part of the ListHeaderComponent or ListFooterComponent props of the FlatList. This way, you can still achieve the desired layout without nesting virtualized Lists.

renderItem={({ item }) => <ItemComponent item={item} />}
ListHeaderComponent={<ComponentAboveFlatlist />}
ListFooterComponent={<ComponentBelowFlatlist />}

Use SectionList: If your data is organized into sections and you need a more complex layout, consider using SectionList, which allows you to create a list with section headers and items within each section.

renderItem={({ item }) => <ItemComponent item={item} />}
renderSectionHeader={({ section }) => <SectionHeaderComponent section={section} />}

Avoid nesting virtualized lists like FlatList or SectionList inside a ScrollView unless you have a specific and valid use case for it, as it can lead to performance issues and unpredictable behavior. Instead, try to structure your components and layout in a way that utilizes the capabilities of a single virtualized list or combines them with other components to achieve your desired UI.

What are the consequence on using Flatlist inside scrollview?

Performance Issues: Virtualized lists like FlatList are optimized for rendering only the items that are currently visible on the screen. When you nest a virtualized list within a ScrollView, both the ScrollView and the inner FlatList will attempt to manage scrolling independently. This can result in performance degradation as both components compete for control over the scroll behavior.

Unpredictable Scrolling Behavior: When you have nested scrolling components, it can lead to unpredictable scrolling behavior. Users may experience difficulties in smoothly scrolling through the content, and it can be challenging to coordinate the scroll positions of the two components effectively.

Difficulty in Handling Events: Handling touch events, such as taps and gestures, can become complicated when you have nested scroll views. It can be challenging to determine which component should respond to a particular event, leading to a less intuitive user experience.

Layout Issues: It can be challenging to create a consistent and responsive layout when using nested scroll views. The inner FlatList may not behave as expected, and it can be difficult to control the layout of elements within the ScrollView.

Performance Degradation: Rendering multiple virtualized lists within a ScrollView can consume more memory and CPU resources than necessary. This can result in slower app performance and increased battery consumption, especially on mobile devices.

Please do Comment if any queries, Thank you...!

Top comments (0)