This is documentation for the next SDK version. For up-to-date documentation, see the latest version (SDK 51).
A library that provides access to the device's magnetometer sensor.
Magnetometer
from expo-sensors
provides access to the device magnetometer sensor(s) to respond to and measure the changes in the magnetic field measured in microtesla (μT
).
You can access the calibrated values with Magnetometer
and uncalibrated raw values with MagnetometerUncalibrated
.
-
npx expo install expo-sensors
If you are installing this in an existing React Native app (bare workflow), start by installing expo
in your project. Then, follow the additional instructions as mentioned by library's README under "Installation in bare React Native projects" section.
import React, { useState, useEffect } from 'react';
import { StyleSheet, Text, TouchableOpacity, View } from 'react-native';
import { Magnetometer } from 'expo-sensors';
export default function Compass() {
const [{ x, y, z }, setData] = useState({
x: 0,
y: 0,
z: 0,
});
const [subscription, setSubscription] = useState(null);
const _slow = () => Magnetometer.setUpdateInterval(1000);
const _fast = () => Magnetometer.setUpdateInterval(16);
const _subscribe = () => {
setSubscription(
Magnetometer.addListener(result => {
setData(result);
})
);
};
const _unsubscribe = () => {
subscription && subscription.remove();
setSubscription(null);
};
useEffect(() => {
_subscribe();
return () => _unsubscribe();
}, []);
return (
<View style={styles.container}>
<Text style={styles.text}>Magnetometer:</Text>
<Text style={styles.text}>x: {x}</Text>
<Text style={styles.text}>y: {y}</Text>
<Text style={styles.text}>z: {z}</Text>
<View style={styles.buttonContainer}>
<TouchableOpacity onPress={subscription ? _unsubscribe : _subscribe} style={styles.button}>
<Text>{subscription ? 'On' : 'Off'}</Text>
</TouchableOpacity>
<TouchableOpacity onPress={_slow} style={[styles.button, styles.middleButton]}>
<Text>Slow</Text>
</TouchableOpacity>
<TouchableOpacity onPress={_fast} style={styles.button}>
<Text>Fast</Text>
</TouchableOpacity>
</View>
</View>
);
}
const styles = StyleSheet.create({
container: {
flex: 1,
justifyContent: 'center',
paddingHorizontal: 10,
},
text: {
textAlign: 'center',
},
buttonContainer: {
flexDirection: 'row',
alignItems: 'stretch',
marginTop: 15,
},
button: {
flex: 1,
justifyContent: 'center',
alignItems: 'center',
backgroundColor: '#eee',
padding: 10,
},
middleButton: {
borderLeftWidth: 1,
borderRightWidth: 1,
borderColor: '#ccc',
},
});
import { Magnetometer, MagnetometerUncalibrated } from 'expo-sensors';
Magnetometer
Type: Class extends DeviceSensor<MagnetometerMeasurement>
Magnetometer Methods
addListener(listener)
Name | Type | Description |
---|---|---|
listener | Listener<MagnetometerMeasurement> | A callback that is invoked when a magnetometer update is available.
When invoked, the listener is provided with a single argument that is |
Subscribe for updates to the magnetometer.
EventSubscription
A subscription that you can call remove()
on when you would like to unsubscribe the listener.
hasListeners()
Returns boolean which signifies if sensor has any listeners registered.
boolean
isAvailableAsync()
You should always check the sensor availability before attempting to use it.
Check the availability of the device magnetometer. Requires at least Android 2.3 (API Level 9) and iOS 8.
Promise<boolean>
A promise that resolves to a boolean
denoting the availability of the sensor.
removeSubscription(subscription)
Name | Type | Description |
---|---|---|
subscription | EventSubscription | A subscription to remove. |
Removes the given subscription.
void
setUpdateInterval(intervalMs)
Name | Type | Description |
---|---|---|
intervalMs | number | Desired interval in milliseconds between sensor updates.
|
Set the sensor update interval.
void
PermissionResponse
An object obtained by permissions get and request functions.
PermissionResponse Properties
Name | Type | Description |
---|---|---|
canAskAgain | boolean | Indicates if user can be asked again for specific permission. If not, one should be directed to the Settings app in order to enable/disable the permission. |
expires | PermissionExpiration | Determines time when the permission expires. |
granted | boolean | A convenience boolean that indicates if the permission is granted. |
status | PermissionStatus | Determines the status of the permission. |
MagnetometerMeasurement
Each of these keys represents the strength of magnetic field along that particular axis measured in microteslas (μT
).
Name | Type | Description |
---|---|---|
timestamp | number | Timestamp of the measurement in seconds. |
x | number | Value representing strength of magnetic field recorded in X axis. |
y | number | Value representing strength of magnetic field recorded in Y axis. |
z | number | Value representing strength of magnetic field recorded in Z axis. |
PermissionExpiration
Literal Type: multiple types
Permission expiration time. Currently, all permissions are granted permanently.
Acceptable values are: 'never'
| number
Subscription
A subscription object that allows to conveniently remove an event listener from the emitter.
Name | Type | Description |
---|---|---|
remove | () => void | Removes an event listener for which the subscription has been created. After calling this function, the listener will no longer receive any events from the emitter. |
UNDETERMINED
PermissionStatus.UNDETERMINED = "undetermined"
User hasn't granted or denied the permission yet.