useNativeState

A React hook that creates observable state shared between JavaScript and native Jetpack Compose views.

Android

Included in Expo Go

GitHub

npm

Changelog

Bundled version:

~56.0.2

useNativeState returns an ObservableState that maps to a Compose MutableState on the native side, so reads and writes to .value are tracked directly by Compose without going through the React render cycle. This lets you update the native view synchronously from a worklet on the UI thread.

Installation

Terminal

- npx expo install @expo/ui

If you are installing this in an existing React Native app, make sure to install expo in your project.

Usage

Note: Using worklets requires installing react-native-reanimated and react-native-worklets in your project. useNativeState itself works without them, but the synchronous UI-thread updates shown below depend on the worklet runtime.

The example below masks a phone number as the user types. The formatting and the writes to maskedPhone.value (text) and selection.value (cursor position) all happen synchronously on the UI thread, so there is no flicker between the typed value and the masked value.

WorkletPhoneMaskExample.tsx

import { Host, TextField, Text as ComposeText, useNativeState } from '@expo/ui/jetpack-compose';
import { fillMaxWidth } from '@expo/ui/jetpack-compose/modifiers';

export default function WorkletPhoneMaskExample() {
  const maskedPhone = useNativeState('');
  const selection = useNativeState({ start: 0, end: 0 });

  return (
    <Host matchContents>
      <TextField
        value={maskedPhone}
        selection={selection}
        keyboardOptions={{ keyboardType: 'phone' }}
        modifiers={[fillMaxWidth()]}
        onValueChange={v => {
          'worklet';
          const digits = v.replace(/\D/g, '').slice(0, 10);
          let formatted: string;
          if (digits.length === 0) {
            formatted = '';
          } else if (digits.length <= 3) {
            formatted = digits;
          } else if (digits.length <= 6) {
            formatted = `(${digits.slice(0, 3)}) ${digits.slice(3)}`;
          } else {
            formatted = `(${digits.slice(0, 3)}) ${digits.slice(3, 6)}-${digits.slice(6)}`;
          }
          if (formatted !== v) {
            maskedPhone.value = formatted;
            selection.value = { start: formatted.length, end: formatted.length };
          }
        }}>
        <TextField.Placeholder>
          <ComposeText>(555) 123-4567</ComposeText>
        </TextField.Placeholder>
      </TextField>
    </Host>
  );
}

API

import { useNativeState } from '@expo/ui/jetpack-compose';

Hooks

`useNativeState(initialValue)`

Android

Parameter	Type
initialValue	`T`

Creates an observable native state that is automatically cleaned up when the component unmounts.

Returns:

ObservableState<T>

Types

`ObservableState`

Android

Observable state shared between JavaScript and native views (Jetpack Compose on Android and SwiftUI on iOS).

Type: SharedObject extended by:

Property	Type	Description
value	`T`	The current value. Reads are safe from any thread; prefer writing from a worklet so the update runs on the native UI thread. Updating state from the JS thread might show a development warning.