Expo DeviceMotionA library that provides access to a device's motion and orientation sensors.
DeviceMotion from expo-sensors provides access to the device motion and orientation sensors. All data is presented in terms of three axes that run through a device. According to portrait orientation: X runs from left to right, Y from bottom to top and Z perpendicularly through the screen from back to front.
Installation
- npx expo install expo-sensorsIf you are installing this in an existing React Native app, start by installing expo in your project. Then, follow the additional instructions as mentioned by the library's README under "Installation in bare React Native projects" section.
Configuration in app.json/app.config.js
You can configure DeviceMotion from expo-sensor using its built-in config plugin if you use config plugins in your project (EAS Build or npx expo run:[android|ios]). The plugin allows you to configure various properties that cannot be set at runtime and require building a new app binary to take effect.
Example app.json with config plugin
{
"expo": {
"plugins": [
[
"expo-sensors",
{
"motionPermission": "Allow $(PRODUCT_NAME) to access your device motion."
}
]
]
}
}
Configurable properties
| Name | Default | Description |
|---|---|---|
motionPermission | "Allow $(PRODUCT_NAME) to access your device motion" | Only for: iOS A string to set the |
Are you using this library in a bare React Native app?
Learn how to configure the native projects in the installation instructions in the expo-sensors repository.
API
import { DeviceMotion } from 'expo-sensors';
Constants
Gravity
Type: number
Constant value representing standard gravitational acceleration for Earth (9.80665 m/s^2).
Classes
DeviceMotion
Type: Class extends DeviceSensor<DeviceMotionMeasurement>
A base class for subscribable sensors. The events emitted by this class are measurements
specified by the parameter type Measurement.
DeviceMotion Properties
Gravity
number • Default: ExponentDeviceMotion.GravityConstant value representing standard gravitational acceleration for Earth (9.80665 m/s^2).
DeviceMotion Methods
addListener(listener)
| Parameter | Type | Description |
|---|---|---|
| listener | Listener<DeviceMotionMeasurement> | A callback that is invoked when a device motion sensor update is available. When invoked,
the listener is provided a single argument that is a |
Subscribe for updates to the device motion sensor.
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.
Returns whether the accelerometer is enabled on the device.
On mobile web, you must first invoke DeviceMotion.requestPermissionsAsync() in a user interaction (i.e. touch event) before you can use this module.
If the status is not equal to granted then you should inform the end user that they may have to open settings.
On web this starts a timer and waits to see if an event is fired. This should predict if the iOS device has the device orientation API disabled in
Settings > Safari > Motion & Orientation Access. Some devices will also not fire if the site isn't hosted with HTTPS as DeviceMotion is now considered a secure API.
There is no formal API for detecting the status of DeviceMotion so this API can sometimes be unreliable on web.
Promise<boolean>
A promise that resolves to a boolean denoting the availability of device motion sensor.
removeSubscription(subscription)
| Parameter | Type | Description |
|---|---|---|
| subscription | EventSubscription | A subscription to remove. |
Removes the given subscription.
void
requestPermissionsAsync()
Asks the user to grant permissions for accessing sensor.
setUpdateInterval(intervalMs)
| Parameter | Type | Description |
|---|---|---|
| intervalMs | number | Desired interval in milliseconds between sensor updates.
|
Set the sensor update interval.
void
Interfaces
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. |
Types
DeviceMotionMeasurement
| Name | Type | Description |
|---|---|---|
| acceleration | null | {
timestamp: number,
x: number,
y: number,
z: number
} | Device acceleration on the three axis as an object with |
| accelerationIncludingGravity | {
timestamp: number,
x: number,
y: number,
z: number
} | Device acceleration with the effect of gravity on the three axis as an object with |
| interval | number | Interval at which data is obtained from the native platform. Expressed in milliseconds (ms). |
| orientation | DeviceMotionOrientation | Device orientation based on screen rotation. Value is one of:
|
| rotation | {
alpha: number,
beta: number,
gamma: number,
timestamp: number
} | Device's orientation in space as an object with alpha, beta, gamma keys where alpha is for rotation around Z axis, beta for X axis rotation and gamma for Y axis rotation. |
| rotationRate | null | {
alpha: number,
beta: number,
gamma: number,
timestamp: number
} | Device's rate of rotation in space expressed in degrees per second (deg/s). |
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. |
Enums
LeftLandscape
DeviceMotionOrientation.LeftLandscape ＝ -90Portrait
DeviceMotionOrientation.Portrait ＝ 0RightLandscape
DeviceMotionOrientation.RightLandscape ＝ 90UpsideDown
DeviceMotionOrientation.UpsideDown ＝ 180UNDETERMINED
PermissionStatus.UNDETERMINED ＝ "undetermined"User hasn't granted or denied the permission yet.
Permissions
iOS
The following usage description keys are used by this library:
| Info.plist Key | Description |
|---|---|
| A message that tells the user why the app is requesting access to the device’s motion data. |