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Expo 媒体库
一个提供访问设备媒体库的库。
expo-media-library 提供对用户媒体库的访问,使他们能够在你的应用中访问现有的图像和视频,并保存新的内容。你还可以订阅用户媒体库中的任何更新。
Android 仅允许对媒体库进行完整访问(这也是此包的用途),且仅适用于需要广泛访问照片的应用。请参阅 Google Play 的照片和视频权限政策详情。
安装
If you are installing this in an existing React Native app, make sure to install expo in your project.
app 配置中的配置
如果你的项目使用配置插件(Continuous Native Generation(CNG)),你可以使用 expo-media-library 内置的 配置插件进行配置。该插件允许你配置各种无法在运行时设置、且需要重新构建新的应用二进制文件后才会生效的属性。如果你的应用没有使用 CNG,那么你需要手动配置此库。
Example app.json with config plugin
{ "expo": { "plugins": [ [ "expo-media-library", { "photosPermission": "Allow $(PRODUCT_NAME) to access your photos.", "savePhotosPermission": "Allow $(PRODUCT_NAME) to save photos.", "isAccessMediaLocationEnabled": true, "granularPermissions": ["audio", "photo"] } ] ] } }
Configurable properties
Are you using this library in an existing React Native app?
如果你没有使用 Continuous Native Generation(CNG),或者你正在手动使用原生 android 和 ios 项目,那么你需要向原生项目添加以下权限和配置:
Android
-
要访问资源位置(纬度和经度 EXIF 标签),请将
ACCESS_MEDIA_LOCATION权限添加到项目的 android/app/src/main/AndroidManifest.xml:<uses-permission android:name="android.permission.ACCESS_MEDIA_LOCATION" /> -
作用域存储 从 Android 10 开始可用。要让
expo-media-library在作用域存储下正常工作,你需要将以下配置添加到 android/app/src/main/AndroidManifest.xml:<manifest ... > <application android:requestLegacyExternalStorage="true" ...> </manifest>
iOS
-
将
NSPhotoLibraryUsageDescription和NSPhotoLibraryAddUsageDescription键添加到项目的 ios/[app]/Info.plist:<key>NSPhotoLibraryUsageDescription</key> <string>授予 $(PRODUCT_NAME) 访问你照片的权限</string> <key>NSPhotoLibraryAddUsageDescription</key> <string>授予 $(PRODUCT_NAME) 保存照片的权限</string>
用法
已知限制
空相册
由于 Android 的系统限制,无法创建空相册。必须传入一个现有资源以添加到相册,或者传入一个本地资源的 URI,系统会用它在相册中创建一个新资源。
在相册之间移动资源
Android 11 引入了权限变化,使得在相册之间移动资源的操作每次都需要用户确认。
因此,在创建新资源时,建议不要先创建资源再将其移动到相册,而是将 album 参数传递给 createAssetAsync 方法,这样会自动将资源添加到相册,而无需用户确认。
图片方向错误
在 Android 上,使用 getAssetsAsync 时如果没有设置 resolveWithFullInfo: true,图像方向可能不正确,因为 EXIF 数据(其中包含方向信息)只有在启用该选项时才会读取。
API
import * as MediaLibrary from 'expo-media-library';
Component
Type: React.Element<AlbumsOptions>
Queries for user-created albums in media gallery.
Constants
Type: SortByObject
Supported keys that can be used to sort getAssetsAsync results.
Hooks
Check or request permissions to access the media library.
This uses both requestPermissionsAsync and getPermissionsAsync to interact with the permissions.
[null | PermissionResponse, RequestPermissionMethod<PermissionResponse>, GetPermissionMethod<PermissionResponse>]Example
const [permissionResponse, requestPermission] = MediaLibrary.usePermissions();
Methods
Adds array of assets to the album.
On Android, by default it copies assets from the current album to provided one, however it's also
possible to move them by passing false as copyAssets argument. In case they're copied you
should keep in mind that getAssetsAsync will return duplicated assets.
Promise<boolean>Returns promise which fulfils with true if the assets were successfully added to
the album.
Checks if the album should be migrated to a different location. In other words, it checks if the
application has the write permission to the album folder. If not, it returns true, otherwise false.
Note: For Android below R, web or iOS, this function always returns
false.
Promise<boolean>Returns a promise which fulfils with true if the album should be migrated.
Creates an album with given name and initial asset. The asset parameter is required on Android,
since it's not possible to create empty album on this platform. On Android, by default it copies
given asset from the current album to the new one, however it's also possible to move it by
passing false as copyAsset argument.
In case it's copied you should keep in mind that getAssetsAsync will return duplicated asset.
On Android, it's not possible to create an empty album. You must provide an existing asset to copy or move into the album or an uri of a local file, which will be used to create an initial asset for the album.
Newly created Album.
Creates an asset from existing file. The most common use case is to save a picture taken by Camera.
This method requires CAMERA_ROLL permission.
A promise which fulfils with an object representing an Asset.
Example
const { uri } = await Camera.takePictureAsync(); const asset = await MediaLibrary.createAssetAsync(uri);
Deletes given albums from the library. On Android by default it deletes assets belonging to given
albums from the library. On iOS it doesn't delete these assets, however it's possible to do by
passing true as deleteAssets.
Promise<boolean>Returns a promise which fulfils with true if the albums were successfully deleted from
the library.
Deletes assets from the library. On iOS it deletes assets from all albums they belong to, while on Android it keeps all copies of them (album is strictly connected to the asset). Also, there is additional dialog on iOS that requires user to confirm this action.
Promise<boolean>Returns promise which fulfils with true if the assets were successfully deleted.
Checks user's permissions for accessing media library.
Promise<PermissionResponse>A promise that fulfils with PermissionResponse object.
Returns whether the Media Library API is enabled on the current device.
Promise<boolean>A promise which fulfils with a boolean, indicating whether the Media Library API is
available on the current device.
Moves album content to the special media directories on Android R or above if needed.
Those new locations are in line with the Android scoped storage - so your application won't
lose write permission to those directories in the future.
This method does nothing if:
- app is running on iOS, web or Android below R
- app has write permission to the album folder
The migration is possible when the album contains only compatible files types.
For instance, movies and pictures are compatible with each other, but music and pictures are not.
If automatic migration isn't possible, the function rejects.
In that case, you can use methods from the expo-file-system to migrate all your files manually.
Why do you need to migrate files?
Android R introduced a lot of changes in the storage system. Now applications can't save
anything to the root directory. The only available locations are from the MediaStore API.
Unfortunately, the media library stored albums in folders for which, because of those changes,
the application doesn't have permissions anymore. However, it doesn't mean you need to migrate
all your albums. If your application doesn't add assets to albums, you don't have to migrate.
Everything will work as it used to. You can read more about scoped storage in the Android documentation.
Promise<void>A promise which fulfils to void.
Allows the user to update the assets that your app has access to.
The system modal is only displayed if the user originally allowed only limited access to their
media library, otherwise this method is a no-op.
Promise<void>A promise that either rejects if the method is unavailable, or resolves to void.
Note: This method doesn't inform you if the user changes which assets your app has access to. That information is only exposed by iOS, and to obtain it, you need to subscribe for updates to the user's media library using
addListener(). IfhasIncrementalChangesisfalse, the user changed their permissions.
Removes given assets from album.
On Android, album will be automatically deleted if there are no more assets inside.
Promise<boolean>Returns promise which fulfils with true if the assets were successfully removed from
the album.
Asks the user to grant permissions for accessing media in user's media library.
Promise<PermissionResponse>A promise that fulfils with PermissionResponse object.
Saves the file at given localUri to the user's media library. Unlike createAssetAsync(),
This method doesn't return created asset.
On iOS 11+, it's possible to use this method without asking for CAMERA_ROLL permission,
however then yours Info.plist should have NSPhotoLibraryAddUsageDescription key.
Promise<void>Event subscriptions
Subscribes for updates in user's media library.
EventSubscriptionAn Subscription object that you can call remove() on when you would
like to unsubscribe the listener.
Interfaces
A subscription object that allows to conveniently remove an event listener from the emitter.
Types
Literal type: string
Determines the type of media that the app will ask the OS to get access to.
Acceptable values are: 'audio' | 'photo' | 'video'
Literal type: string
Constants identifying specific variations of asset media, such as panorama or screenshot photos,
and time-lapse or high-frame-rate video. Maps to PHAssetMediaSubtype.
Acceptable values are: 'depthEffect' | 'hdr' | 'highFrameRate' | 'livePhoto' | 'panorama' | 'screenshot' | 'stream' | 'timelapse' | 'spatialMedia' | 'videoCinematic'
Literal type: string
Represents the possible types of media that the app will ask the OS to get access to when calling presentPermissionsPickerAsync().
Acceptable values are: 'photo' | 'video'
Literal type: string
Acceptable values are: 'audio' | 'photo' | 'video' | 'unknown' | 'pairedVideo'
Literal type: union
Permission expiration time. Currently, all permissions are granted permanently.
Acceptable values are: 'never' | number
Literal type: union
Acceptable values are: PermissionHookBehavior | Options
Literal type: string
Acceptable values are: 'default' | 'mediaType' | 'width' | 'height' | 'creationTime' | 'modificationTime' | 'duration'
Enums
权限
Android
以下权限会通过此库的 AndroidManifest.xml 自动添加:
iOS
以下使用说明键会被此库使用: