Expo 相机

一个 React 组件，用于渲染设备前置或后置摄像头的预览。

Web

expo-camera 提供了一个 React 组件，可以渲染设备前置或后置摄像头的预览。相机的变焦、手电筒和闪光模式等参数均可调节。使用 CameraView，你可以拍摄照片和录制视频并保存到应用的缓存中。该组件还能够检测预览中出现的条形码。在你的设备上运行 example 以查看所有这些功能的协同工作。

¥expo-camera provides a React component that renders a preview of the device's front or back camera. The camera's parameters such as zoom, torch, and flash mode are adjustable. Using CameraView, you can take photos and record videos that are saved to the app's cache. The component is also capable of detecting bar codes appearing in the preview. Run the example on your device to see all these features working together.

安装

¥Installation

Terminal

- npx expo install expo-camera

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.

app.json/app.config.js 中的配置

¥Configuration in app.json/app.config.js

如果你在项目中使用配置插件（EAS 构建或 npx expo run:[android|ios]），则可以使用其内置的配置插件配置 expo-camera。该插件允许你配置无法在运行时设置的各种属性，并且需要构建新的应用二进制文件才能生效。

¥You can configure expo-camera 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

app.json

{
  "expo": {
    "plugins": [
      [
        "expo-camera",
        {
          "cameraPermission": "Allow $(PRODUCT_NAME) to access your camera",
          "microphonePermission": "Allow $(PRODUCT_NAME) to access your microphone",
          "recordAudioAndroid": true
        }
      ]
    ]
  }
}

Configurable properties

Name	Default	Description
`cameraPermission`	`"Allow $(PRODUCT_NAME) to access your camera"`	Only for: iOS A string to set the `NSCameraUsageDescription` permission message.
`microphonePermission`	`"Allow $(PRODUCT_NAME) to access your microphone"`	Only for: iOS A string to set the `NSMicrophoneUsageDescription` permission message.
`recordAudioAndroid`	`true`	Only for: Android A boolean that determines whether to enable the `RECORD_AUDIO` permission on Android.

Are you using this library in a bare React Native app?

了解如何在 expo-camera 存储库中的安装说明文件中配置原生项目。

¥Learn how to configure the native projects in the installation instructions in the expo-camera repository.

用法

¥Usage

在任何给定时间只能激活一个相机预览。如果你的应用中有多个屏幕，则只要屏幕未聚焦，你就应该卸载 Camera 组件。

Basic Camera Usage

import { CameraView, CameraType, useCameraPermissions } from 'expo-camera';
import { useState } from 'react';
import { Button, StyleSheet, Text, TouchableOpacity, View } from 'react-native';

export default function App() {
  const [facing, setFacing] = useState<CameraType>('back');
  const [permission, requestPermission] = useCameraPermissions();

  if (!permission) {
    // Camera permissions are still loading.
    return <View />;
  }

  if (!permission.granted) {
    // Camera permissions are not granted yet.
    return (
      <View style={styles.container}>
        <Text style={styles.message}>We need your permission to show the camera</Text>
        <Button onPress={requestPermission} title="grant permission" />
      </View>
    );
  }

  function toggleCameraFacing() {
    setFacing(current => (current === 'back' ? 'front' : 'back'));
  }

  return (
    <View style={styles.container}>
      <CameraView style={styles.camera} facing={facing}>
        <View style={styles.buttonContainer}>
          <TouchableOpacity style={styles.button} onPress={toggleCameraFacing}>
            <Text style={styles.text}>Flip Camera</Text>
          </TouchableOpacity>
        </View>
      </CameraView>
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
  },
  message: {
    textAlign: 'center',
    paddingBottom: 10,
  },
  camera: {
    flex: 1,
  },
  buttonContainer: {
    flex: 1,
    flexDirection: 'row',
    backgroundColor: 'transparent',
    margin: 64,
  },
  button: {
    flex: 1,
    alignSelf: 'flex-end',
    alignItems: 'center',
  },
  text: {
    fontSize: 24,
    fontWeight: 'bold',
    color: 'white',
  },
});

Web 支持

¥Web support

大多数浏览器都支持网络摄像头功能的版本，你可以查看网络摄像头浏览器支持在这里。图片 URI 始终以 base64 字符串形式返回，因为本地文件系统路径在浏览器中不可用。

¥Most browsers support a version of web camera functionality, you can check out the web camera browser support here. Image URIs are always returned as base64 strings because local file system paths are unavailable in the browser.

Chrome `iframe` 使用情况

¥Chrome iframe usage

使用 Chrome 版本 64+ 时，如果你尝试在跨源 iframe 中使用网络摄像头，则不会渲染任何内容。要在 iframe 中添加对摄像头的支持，只需将属性 allow="microphone; camera;" 添加到 iframe 元素即可：

¥When using Chrome versions 64+, if you try to use a web camera in a cross-origin iframe nothing will render. To add support for cameras in your iframe simply add the attribute allow="microphone; camera;" to the iframe element:

<iframe src="..." allow="microphone; camera;">
  <!-- <CameraView /> -->
</iframe>

API

import { CameraView } from 'expo-camera';

Component

`CameraView`

Type: React.Component<CameraProps>

CameraViewProps

Only for:

iOS

`active`

Optional • Type: boolean • Default: true

A boolean that determines whether the camera should be active. Useful in situations where the camera may not have unmounted but you still want to stop the camera session.

`animateShutter`

Optional • Type: boolean • Default: true

A boolean that determines whether the camera shutter animation should be enabled.

Only for:

iOS

`autofocus`

Optional • Type: FocusMode • Default: off

Indicates the focus mode to use.

`barcodeScannerSettings`

Optional • Type: BarcodeSettings

Example

<CameraView
  barcodeScannerSettings={{
    barcodeTypes: ["qr"],
  }}
/>

`enableTorch`

Optional • Type: boolean • Default: false

A boolean to enable or disable the torch

`facing`

Optional • Type: CameraType • Default: 'back'

Camera facing. Use one of CameraType. When front, use the front-facing camera. When back, use the back-facing camera.

`flash`

Optional • Type: FlashMode • Default: 'off'

Camera flash mode. Use one of FlashMode values. When on, the flash on your device will turn on when taking a picture. When off, it won't. Setting it to auto will fire flash if required.

`mirror`

Optional • Type: boolean • Default: false

A boolean that determines whether the camera should mirror the image when using the front camera.

`mode`

Optional • Type: CameraMode • Default: 'picture'

Used to select image or video output

`mute`

Optional • Type: boolean • Default: false

If present, video will be recorded with no sound.

`onBarcodeScanned`

Optional • Type: (scanningResult: BarcodeScanningResult) => void

Callback that is invoked when a barcode has been successfully scanned. The callback is provided with an object of the BarcodeScanningResult shape, where the type refers to the barcode type that was scanned, and the data is the information encoded in the barcode (in this case of QR codes, this is often a URL). See BarcodeType for supported values. for supported values.

`onCameraReady`

Optional • Type: () => void

Callback invoked when camera preview has been set.

`onMountError`

Optional • Type: (event: CameraMountError) => void

Callback invoked when camera preview could not start.

Only for:

iOS

`onResponsiveOrientationChanged`

Optional • Type: (event: ResponsiveOrientationChanged) => void

Callback invoked when responsive orientation changes. Only applicable if responsiveOrientationWhenOrientationLocked is true

`pictureSize`

Optional • Type: string

A string representing the size of pictures takePictureAsync will take. Available sizes can be fetched with getAvailablePictureSizesAsync. Setting this prop will cause the ratio prop to be ignored as the aspect ratio is determined by the selected size.

Only for:

Web

`poster`

Optional • Type: string

A URL for an image to be shown while the camera is loading.

Only for:

Android

`ratio`

Optional • Type: CameraRatio • Default: 1:1

A string representing the aspect ratio of the preview. For example, 4:3 and 16:9. Note: Setting the aspect ratio here will change the scaleType of the camera preview from FILL to FIT.

Only for:

iOS

`responsiveOrientationWhenOrientationLocked`

Optional • Type: boolean

Whether to allow responsive orientation of the camera when the screen orientation is locked (i.e. when set to true landscape photos will be taken if the device is turned that way, even if the app or device orientation is locked to portrait)

`videoQuality`

Optional • Type: VideoQuality

Specify the quality of the recorded video. Use one of VideoQuality possible values: for 16:9 resolution 2160p, 1080p, 720p, 480p : Android only and for 4:3 4:3 (the size is 640x480). If the chosen quality is not available for a device, the highest available is chosen.

Only for:

iOS

`videoStabilizationMode`

Optional • Type: VideoStabilization

The video stabilization mode used for a video recording. Use one of VideoStabilization.<value>. You can read more about each stabilization type in Apple Documentation.

`zoom`

Optional • Type: number • Default: 0

A value between 0 and 1 being a percentage of device's max zoom. 0 - not zoomed, 1 - maximum zoom.

Inherited Props

ViewProps

Static Methods

Only for:

iOS

`dismissScanner()`

Dismiss the scanner presented by launchScanner.

Returns:

Promise<void>

Only for:

iOS

`getAvailableVideoCodecsAsync()`

Queries the device for the available video codecs that can be used in video recording.

Returns:

Promise<VideoCodec[]>

A promise that resolves to a list of strings that represents available codecs.

Only for:

Web

`isAvailableAsync()`

Check whether the current device has a camera. This is useful for web and simulators cases. This isn't influenced by the Permissions API (all platforms), or HTTP usage (in the browser). You will still need to check if the native permission has been accepted.

Returns:

Promise<boolean>

Only for:

iOS

`launchScanner(options)`

Name	Type
options (optional)	`ScanningOptions`

Presents a modal view controller that uses the DataScannerViewController available on iOS 16+.

Returns:

Promise<void>

Only for:

iOS

`onModernBarcodeScanned(listener)`

Name	Type	Description
listener	`(event: ScanningResult) => void`	Invoked with the ScanningResult when a bar code has been successfully scanned.

Invokes the listener function when a bar code has been successfully scanned. The callback is provided with an object of the ScanningResult shape, where the type refers to the bar code type that was scanned and the data is the information encoded in the bar code (in this case of QR codes, this is often a URL). See BarcodeType for supported values.

Returns:

EventSubscription

Component Methods

`getAvailablePictureSizesAsync()`

Get picture sizes that are supported by the device.

Returns:

Promise<string[]>

Returns a Promise that resolves to an array of strings representing picture sizes that can be passed to pictureSize prop. The list varies across Android devices but is the same for every iOS.

`pausePreview()`

Pauses the camera preview. It is not recommended to use takePictureAsync when preview is paused.

Returns:

Promise<void>

Only for:

Android

iOS

`recordAsync(options)`

Name	Type	Description
options (optional)	`CameraRecordingOptions`	A map of `CameraRecordingOptions` type.

Starts recording a video that will be saved to cache directory. Videos are rotated to match device's orientation. Flipping camera during a recording results in stopping it.

Returns:

Promise<undefined | { uri: string }>

Returns a Promise that resolves to an object containing video file uri property and a codec property on iOS. The Promise is returned if stopRecording was invoked, one of maxDuration and maxFileSize is reached or camera preview is stopped.

`resumePreview()`

Resumes the camera preview.

Returns:

Promise<void>

`stopRecording()`

Stops recording if any is in progress.

Returns:

void

`takePictureAsync(options)`

Name	Type	Description
options (optional)	`CameraPictureOptions`	An object in form of `CameraPictureOptions` type.

Takes a picture and saves it to app's cache directory. Photos are rotated to match device's orientation (if options.skipProcessing flag is not enabled) and scaled to match the preview.

Note: Make sure to wait for the onCameraReady callback before calling this method.

Returns:

Promise<undefined | CameraCapturedPicture>

Returns a Promise that resolves to CameraCapturedPicture object, where uri is a URI to the local image file on Android, iOS, and a base64 string on web (usable as the source for an Image element). The width and height properties specify the dimensions of the image.

base64 is included if the base64 option was truthy, and is a string containing the JPEG data of the image in Base64. Prepend it with 'data:image/jpg;base64,' to get a data URI, which you can use as the source for an Image element for example.

exif is included if the exif option was truthy, and is an object containing EXIF data for the image. The names of its properties are EXIF tags and their values are the values for those tags.

On native platforms, the local image URI is temporary. Use FileSystem.copyAsync to make a permanent copy of the image.

Note Avoid calling this method while the preview is paused. On iOS, this will take a picture of the last frame that is currently on screen, on Android, this will throw an error.

Hooks

`useCameraPermissions(options)`

Name	Type
options (optional)	`PermissionHookOptions<object>`

Check or request permissions to access the camera. This uses both requestCameraPermissionsAsync and getCameraPermissionsAsync to interact with the permissions.

Returns:

[null | PermissionResponse, RequestPermissionMethod<PermissionResponse>, GetPermissionMethod<PermissionResponse>]

Example

const [status, requestPermission] = useCameraPermissions();

`useMicrophonePermissions(options)`

Name	Type
options (optional)	`PermissionHookOptions<object>`

Check or request permissions to access the microphone. This uses both requestMicrophonePermissionsAsync and getMicrophonePermissionsAsync to interact with the permissions.

Returns:

[null | PermissionResponse, RequestPermissionMethod<PermissionResponse>, GetPermissionMethod<PermissionResponse>]

Example

const [status, requestPermission] = Camera.useMicrophonePermissions();

Methods

`Camera.scanFromURLAsync(url, barcodeTypes)`

Name Type Description

Name	Type	Description
url	`string`	URL to get the image from.
barcodeTypes (optional)	`BarcodeType[]`	An array of bar code types. Defaults to all supported bar code types on the platform. Note: Only QR codes are supported on iOS. On android, the barcode should take up the majority of the image for best results.

url

string

URL to get the image from.

barcodeTypes
(optional)

BarcodeType[]

An array of bar code types. Defaults to all supported bar code types on the platform.

Note: Only QR codes are supported on iOS. On android, the barcode should take up the majority of the image for best results.

Scan bar codes from the image at the given URL.

Returns:

Promise<BarcodeScanningResult[]>

A possibly empty array of objects of the BarcodeScanningResult shape, where the type refers to the barcode type that was scanned and the data is the information encoded in the barcode.

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

`BarcodeBounds`

Name	Type	Description
origin	`BarcodePoint`	The origin point of the bounding box.
size	`BarcodeSize`	The size of the bounding box.

`BarcodePoint`

Type: Point

These coordinates are represented in the coordinate space of the camera source (e.g. when you are using the camera view, these values are adjusted to the dimensions of the view).

`BarcodeScanningResult`

Name	Type	Description
bounds	`BarcodeBounds`	The BarcodeBounds object. `bounds` in some case will be representing an empty rectangle. Moreover, `bounds` doesn't have to bound the whole barcode. For some types, they will represent the area used by the scanner.
cornerPoints	`BarcodePoint[]`	Corner points of the bounding box. `cornerPoints` is not always available and may be empty. On iOS, for `code39` and `pdf417` you don't get this value.
data	`string`	The parsed information encoded in the barcode.
type	`string`	The barcode type.

`BarcodeSettings`

Name	Type	Description
barcodeTypes	`BarcodeType[]`	-

`BarcodeSize`

Name	Type	Description
height	`number`	The height value.
width	`number`	The width value.

`BarcodeType`

Literal Type: string

The available barcode types that can be scanned.

`CameraCapturedPicture`

Name	Type	Description
base64 (optional)	`string`	A Base64 representation of the image.
exif (optional)	`Partial<MediaTrackSettings> \| any`	On Android and iOS this object may include various fields based on the device and operating system. On web, it is a partial representation of the `MediaTrackSettings` dictionary.
height	`number`	Captured image height.
uri	`string`	On web, the value of `uri` is the same as `base64` because file system URLs are not supported in the browser.
width	`number`	Captured image width.

`CameraMode`

Literal Type: string

Acceptable values are: 'picture' | 'video'

`CameraMountError`

Name	Type	Description
message	`string`	-

`CameraOrientation`

Literal Type: string

Acceptable values are: 'portrait' | 'portraitUpsideDown' | 'landscapeLeft' | 'landscapeRight'

`CameraPictureOptions`

Name	Type	Description
additionalExif (optional)	`Record<string, any>`	Only for: Android iOS Additional EXIF data to be included for the image. Only useful when `exif` option is set to `true`.
base64 (optional)	`boolean`	Whether to also include the image data in Base64 format.
exif (optional)	`boolean`	Whether to also include the EXIF data for the image.
imageType (optional)	`ImageType`	-
isImageMirror (optional)	`boolean`	-
mirror (optional)	`boolean`	Deprecated Use `mirror` prop on `CameraView` instead. Only for: iOS Android When set to `true`, the output image will be flipped along the vertical axis when using the front camera. Default: `false`
onPictureSaved (optional)	`(picture: CameraCapturedPicture) => void`	A callback invoked when picture is saved. If set, the promise of this method will resolve immediately with no data after picture is captured. The data that it should contain will be passed to this callback. If displaying or processing a captured photo right after taking it is not your case, this callback lets you skip waiting for it to be saved.
quality (optional)	`number`	Specify the compression quality from `0` to `1`. `0` means compress for small size, and `1` means compress for maximum quality.
scale (optional)	`number`	-
skipProcessing (optional)	`boolean`	If set to `true`, camera skips orientation adjustment and returns an image straight from the device's camera. If enabled, `quality` option is discarded (processing pipeline is skipped as a whole). Although enabling this option reduces image delivery time significantly, it may cause the image to appear in a wrong orientation in the `Image` component (at the time of writing, it does not respect EXIF orientation of the images). Note: Enabling `skipProcessing` would cause orientation uncertainty. `Image` component does not respect EXIF stored orientation information, that means obtained image would be displayed wrongly (rotated by 90°, 180° or 270°). Different devices provide different orientations. For example some Sony Xperia or Samsung devices don't provide correctly oriented images by default. To always obtain correctly oriented image disable `skipProcessing` option.

`CameraRatio`

Literal Type: string

Acceptable values are: '4:3' | '16:9' | '1:1'

`CameraRecordingOptions`

Name	Type	Description
codec (optional)	`VideoCodec`	Only for: iOS This option specifies what codec to use when recording the video. See `VideoCodec` for the possible values.
maxDuration (optional)	`number`	Maximum video duration in seconds.
maxFileSize (optional)	`number`	Maximum video file size in bytes.
mirror (optional)	`boolean`	Deprecated Use `mirror` prop on `CameraView` instead. If `true`, the recorded video will be flipped along the vertical axis. iOS flips videos recorded with the front camera by default, but you can reverse that back by setting this to `true`. On Android, this is handled in the user's device settings.

`CameraType`

Literal Type: string

Acceptable values are: 'front' | 'back'

`FlashMode`

Literal Type: string

Acceptable values are: 'off' | 'on' | 'auto'

`FocusMode`

Literal Type: string

This option specifies the mode of focus on the device.

on - Indicates that the device should autofocus once and then lock the focus.
off - Indicates that the device should automatically focus when needed.

Acceptable values are: 'on' | 'off'

`ImageType`

Literal Type: string

Acceptable values are: 'png' | 'jpg'

`PermissionExpiration`

Literal Type: multiple types

Permission expiration time. Currently, all permissions are granted permanently.

Acceptable values are: 'never' | number

`PermissionHookOptions`

Literal Type: multiple types

Acceptable values are: PermissionHookBehavior | Options

`Point`

Name	Type	Description
x	`number`	-
y	`number`	-

`ResponsiveOrientationChanged`

Name	Type	Description
orientation	`CameraOrientation`	-

Only for:

iOS

`ScanningOptions`

Name	Type	Description
barcodeTypes	`BarcodeType[]`	The type of codes to scan for.
isGuidanceEnabled (optional)	`boolean`	Guidance text, such as “Slow Down,” appears over the live video. Default: `true`
isHighlightingEnabled (optional)	`boolean`	Indicates whether the scanner displays highlights around recognized items. Default: `false`
isPinchToZoomEnabled (optional)	`boolean`	Indicates whether people can use a two-finger pinch-to-zoom gesture. Default: `true`

`ScanningResult`

Type: Omit<BarcodeScanningResult, 'bounds'>

`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.

Only for:

iOS

`VideoCodec`

Literal Type: string

This option specifies what codec to use when recording a video.

Acceptable values are: 'avc1' | 'hvc1' | 'jpeg' | 'apcn' | 'ap4h'

`VideoQuality`

Literal Type: string

Acceptable values are: '2160p' | '1080p' | '720p' | '480p' | '4:3'

Only for:

iOS

`VideoStabilization`

Literal Type: string

This option specifies the stabilization mode to use when recording a video.

Acceptable values are: 'off' | 'standard' | 'cinematic' | 'auto'

Enums

`PermissionStatus`

PermissionStatus Values

`DENIED`

PermissionStatus.DENIED ＝ "denied"

User has denied the permission.

`GRANTED`

PermissionStatus.GRANTED ＝ "granted"

User has granted the permission.

`UNDETERMINED`

PermissionStatus.UNDETERMINED ＝ "undetermined"

User hasn't granted or denied the permission yet.

权限

¥Permissions

安卓

¥Android

此包会自动向你的应用添加 CAMERA 权限。如果你想录制带有音频的视频，则必须将 RECORD_AUDIO 包含在 app.json 的 expo.android.permissions 数组内。

¥This package automatically adds the CAMERA permission to your app. If you want to record videos with audio, you have to include the RECORD_AUDIO in your app.json inside the expo.android.permissions array.

Android Permission	Description
`CAMERA`	Required to be able to access the camera device.
`RECORD_AUDIO`	Allows an application to record audio.

iOS 系统

¥iOS

该库使用以下用法描述键：

¥The following usage description keys are used by this library:

Info.plist Key	Description
`NSCameraUsageDescription`	A message that tells the user why the app is requesting access to the device’s camera.
`NSMicrophoneUsageDescription`	A message that tells the user why the app is requesting access to the device’s microphone.