react-native-intersection-observer

React Native implementation of the Intersection Observer API to tell you when an element enters or leaves the viewport.

Installation

Install using Yarn:

yarn add react-native-intersection-observer

or NPM:

npm install react-native-intersection-observer --save

Usage

You can pass any component to the <InView />, and it will handle creating the wrapping View component. Add a handler to the onChange method, and control the state in your own component. Any extra props you add to <InView> will be passed to the View component, allowing you to set the style, etc.

import React, { useRef } from 'react';
import { Text } from 'react-native';
import {
  IOScrollView,
  IOScrollViewController,
  InView,
} from 'react-native-intersection-observer';

function Demo() {
  const scrollViewRef = useRef<IOScrollViewController>(null);
  return (
    <IOScrollView ref={scrollViewRef}>
      <Text
        onPress={() => {
          scrollViewRef.current?.scrollToEnd();
        }}
      >
        Scroll to bottom
      </Text>
      <InView onChange={(inView: boolean) => console.log('Inview:', inView)}>
        <Text>
          Plain children are always rendered. Use onChange to monitor state.
        </Text>
      </InView>
    </IOScrollView>
  );
}

export default Demo;

You can also use the threshold prop to control how much of the element must be visible before it is considered in view. A value of 0 (default) triggers as soon as any part of the element is visible, while 1 requires the element to be fully visible within the viewport.

<IOScrollView threshold={0.5}>
  <InView onChange={(inView: boolean) => console.log('Inview:', inView)}>
    <Text>This triggers when at least 50% of the element is visible.</Text>
  </InView>
</IOScrollView>

Please note that the functionality of the InView component is dependent on the use of the withIO higher-order component to wrap your scrollable component. The react-native-intersection-observer library presently offers two frequently used scrollable components: IOScrollView and IOFlatList. It's imperative to utilize the InView component within one of these two components for it to work as intended. If neither IOScrollView nor IOFlatList suits your requirements, you have the flexibility to employ withIO to encapsulate your custom scrollable components.

// IOScrollView definition
import { ForwardRefExoticComponent, RefAttributes } from 'react';
import { ScrollView, ScrollViewProps } from 'react-native';
import { type IOComponentProps, withIO } from 'react-native-intersection-observer';

export type IOScrollViewController = ScrollView;

export type IOScrollViewProps = IOComponentProps & ScrollViewProps;

const IOScrollView = withIO(ScrollView, [
  'scrollTo',
  'scrollToEnd',
  'getScrollResponder',
  'getScrollableNode',
  'getInnerViewNode',
]);

export default IOScrollView as unknown as ForwardRefExoticComponent<
  IOScrollViewProps & RefAttributes<IOScrollViewController>
>;

Furthermore, InView cannot be used within nested scrollable components. It solely monitors the immediate parent's scroll behavior, and scrolling at higher ancestral levels does not trigger InView's visibility callback.

API

IOScrollView

• Props: Inherits ScrollView Props

  Name	Type	Default	Required	Description
  rootMargin	{ top: number; left: number; right: number; bottom: number }	undefined	false	Expands or shrinks the viewport bounds used for intersection detection.
  threshold	number	0	false	A value between 0 and 1 indicating what fraction of the element must be visible before it is considered in view.

• Methods: Inherits ScrollView Methods

IOFlatList Props

• Props: Inherits FlatList Props

  Name	Type	Default	Required	Description
  rootMargin	{ top: number; left: number; right: number; bottom: number }	undefined	false	Expands or shrinks the viewport bounds used for intersection detection.
  threshold	number	0	false	A value between 0 and 1 indicating what fraction of the element must be visible before it is considered in view.

• Methods: Inherits FlatList Methods

InView Props

The <InView /> component also accepts the following props:

Name	Type	Default	Required	Description
as	ComponentType	View	false	Render the wrapping element as this element. Defaults to View.
children	ReactNode		true	Children expects a plain child, to have the <InView /> deal with the wrapping element.
triggerOnce	boolean	false	false	Only trigger this method once
onChange	(inView: boolean) => void		false	Call this function whenever the in view state changes. It will receive the inView boolean, alongside the current IntersectionObserverEntry.

License

react-native-intersection-observer is MIT licensed.