一个提供对设备上本地文件系统访问的库。
expo-file-system 提供对存储在设备上的文件和目录的访问,或者将其作为资产捆绑到本地项目中。它还允许从网络下载文件。
安装
- npx expo install expo-file-systemIf you are installing this in an existing React Native app, make sure to install expo in your project.
用法
import { File, Directory, Paths } from 'expo-file-system';
File 和 Directory 实例持有对文件、内容或资产 URI 的引用。
文件或目录不需要存在 — 只有在使用错误的类来表示现有路径时才会从构造函数抛出错误(因此如果你试图创建一个 File 实例,传入一个已经存在的目录的路径)。
特性
- 同步和异步,读取和写入文件内容的访问
- 创建、修改和删除
- 可用属性,例如
type、size、creationDate等 - 以流的方式读取和写入文件,或使用
FileHandle类 - 使用
downloadFileAsync或expo/fetch轻松下载/上传文件
示例
写入和读取文本文件
import { File, Paths } from 'expo-file-system'; try { const file = new File(Paths.cache, 'example.txt'); file.create(); // 如果文件已经存在或没有权限创建它,可能会抛出错误 file.write('Hello, world!'); console.log(file.textSync()); // Hello, world! } catch (error) { console.error(error); }
使用系统选择器选择文件
与 expo-document-picker 的用法:
import { File } from 'expo-file-system'; import * as DocumentPicker from 'expo-document-picker'; try { const result = await DocumentPicker.getDocumentAsync({ copyToCacheDirectory: true }); const file = new File(result.assets[0]); console.log(file.textSync()); } catch (error) { console.error(error); }
在 Android 上使用内置的 pickFileAsync 或 pickDirectoryAsync 方法:
import { File } from 'expo-file-system'; try { const file = new File.pickFileAsync(); console.log(file.textSync()); } catch (error) { console.error(error); }
下载文件
使用 downloadFileAsync:
import { Directory, File, Paths } from 'expo-file-system'; const url = 'https://pdfobject.com/pdf/sample.pdf'; const destination = new Directory(Paths.cache, 'pdfs'); try { destination.create(); const output = await File.downloadFileAsync(url, destination); console.log(output.exists); // true console.log(output.uri); // 下载文件的路径,例如 '${cacheDirectory}/pdfs/sample.pdf' } catch (error) { console.error(error); }
或者使用 expo/fetch:
import { fetch } from 'expo/fetch'; import { File } from 'expo-file-system'; const url = 'https://pdfobject.com/pdf/sample.pdf'; const response = await fetch(url); const src = new File(Paths.cache, 'file.pdf'); src.write(await response.bytes());
使用 expo/fetch 上传文件
你可以通过 Expo 包内置的 fetch 直接将文件作为 blob 上传:
import { fetch } from 'expo/fetch'; import { File } from 'expo-file-system'; const file = new File(Paths.cache, 'file.txt'); file.write('Hello, world!'); const response = await fetch('https://example.com', { method: 'POST', body: file, });
或者使用 FormData 构造函数:
import { fetch } from 'expo/fetch'; import { File, Paths } from 'expo-file-system'; const file = new File(Paths.cache, 'file.txt'); file.write('Hello, world!'); const formData = new FormData(); formData.append('data', file); const response = await fetch('https://example.com', { method: 'POST', body: formData, });
移动和复制文件
import { Directory, File, Paths } from 'expo-file-system'; try { const file = new File(Paths.document, 'example.txt'); file.create(); console.log(file.uri); // '${documentDirectory}/example.txt' const copiedFile = new File(Paths.cache, 'example-copy.txt'); file.copy(copiedFile); console.log(copiedFile.uri); // '${cacheDirectory}/example-copy.txt' file.move(Paths.cache); console.log(file.uri); // '${cacheDirectory}/example.txt' file.move(new Directory(Paths.cache, 'newFolder')); console.log(file.uri); // '${cacheDirectory}/newFolder/example.txt' } catch (error) { console.error(error); }
使用旧版文件系统 API
import * as FileSystem from 'expo-file-system/legacy'; import { File, Paths } from 'expo-file-system'; try { const file = new File(Paths.cache, 'example.txt'); const content = await FileSystem.readAsStringAsync(file.uri); console.log(content); } catch (error) { console.error(error); }
递归列出目录内容
import { Directory, Paths } from 'expo-file-system'; function printDirectory(directory: Directory, indent: number = 0) { console.log(`${' '.repeat(indent)} + ${directory.name}`); const contents = directory.list(); for (const item of contents) { if (item instanceof Directory) { printDirectory(item, indent + 2); } else { console.log(`${' '.repeat(indent + 2)} - ${item.name} (${item.size} bytes)`); } } } try { printDirectory(new Directory(Paths.cache)); } catch (error) { console.error(error); }
API
Classes
Type: Class extends FileSystemDirectory
Represents a directory on the filesystem.
A Directory instance can be created for any path, and does not need to exist on the filesystem during creation.
The constructor accepts an array of strings that are joined to create the directory URI. The first argument can also be a Directory instance (like Paths.cache).
Example
const directory = new Directory(Paths.cache, "subdirName");
Directory Properties
unionA size of the directory in bytes. Null if the directory does not exist, or it cannot be read.
Acceptable values are: null | number
stringRepresents the directory URI. The field is read-only, but it may change as a result of calling some methods such as move.
Directory Methods
Copies a directory.
void| Parameter | Type |
|---|---|
| options(optional) | DirectoryCreateOptions |
Creates a directory that the current uri points to.
voidDeletes a directory. Also deletes all files and directories inside the directory.
voidRetrieves an object containing properties of a directory.
DirectoryInfoAn object with directory metadata (for example, size, creation date, and so on).
Moves a directory. Updates the uri property that now points to the new location.
void| Parameter | Type | Description |
|---|---|---|
| initialUri(optional) | string | An optional uri pointing to an initial folder on which the directory picker is opened. |
A static method that opens a file picker to select a directory.
On iOS, the selected directory grants temporary read and write access for the current app session only. After the app restarts, you must prompt the user again to regain access.
a Directory instance. On Android, the underlying uri will be a content URI.
Type: Class extends FileSystemFile implements Blob
Represents a file on the filesystem.
A File instance can be created for any path, and does not need to exist on the filesystem during creation.
The constructor accepts an array of strings that are joined to create the file URI. The first argument can also be a Directory instance (like Paths.cache) or a File instance (which creates a new reference to the same file).
Example
const file = new File(Paths.cache, "subdirName", "file.txt");
File Properties
unionA creation time of the file expressed in milliseconds since epoch. Returns null if the file does not exist, cannot be read or the Android version is earlier than API 26.
Acceptable values are: null | number
booleanA boolean representing if a file exists. true if the file exists, false otherwise.
Also, false if the application does not have read access to the file.
unionA md5 hash of the file. Null if the file does not exist, or it cannot be read.
Acceptable values are: null | string
unionA last modification time of the file expressed in milliseconds since epoch. Returns a Null if the file does not exist, or it cannot be read.
Acceptable values are: null | number
numberA size of the file in bytes. 0 if the file does not exist, or it cannot be read.
stringA mime type of the file. An empty string if the file does not exist, or it cannot be read.
stringRepresents the file URI. The field is read-only, but it may change as a result of calling some methods such as move.
File Methods
The arrayBuffer() method of the Blob interface returns a Promise that resolves with the contents of the blob as binary data contained in an ArrayBuffer.
Promise<ArrayBuffer>Retrieves content of the file as base64.
Promise<string>A promise that resolves with the contents of the file as a base64 string.
Retrieves content of the file as base64.
stringThe contents of the file as a base64 string.
Retrieves byte content of the entire file.
Promise<Uint8Array<ArrayBuffer>>A promise that resolves with the contents of the file as a Uint8Array.
Retrieves byte content of the entire file.
Uint8ArrayThe contents of the file as a Uint8Array.
| Parameter | Type | Description |
|---|---|---|
| url | string | The URL of the file to download. |
| destination | Directory | File | The destination directory or file. If a directory is provided, the resulting filename will be determined based on the response headers. |
| options(optional) | DownloadOptions | Download options. When the destination already contains a file, the promise rejects with a |
A static method that downloads a file from the network.
On Android, the response body streams directly into the target file. If the download fails after it starts, a partially written file may remain at the destination. On iOS, the download first completes in a temporary location and the file is moved into place only after success, so no file is left behind when the request fails.
A promise that resolves to the downloaded file. When the server responds with
a non-2xx HTTP status, the promise rejects with an UnableToDownload error whose
message includes the status code. No file is created in that scenario.
Example
const file = await File.downloadFileAsync("https://example.com/image.png", new Directory(Paths.document));
| Parameter | Type |
|---|---|
| options(optional) | InfoOptions |
Retrieves an object containing properties of a file
FileInfoAn object with file metadata (for example, size, creation date, and so on).
Moves a directory. Updates the uri property that now points to the new location.
voidReturns A FileHandle object that can be used to read and write data to the file.
FileHandle| Parameter | Type | Description |
|---|---|---|
| initialUri(optional) | string | An optional URI pointing to an initial folder on which the file picker is opened. |
| mimeType(optional) | string | A mime type that is used to filter out files that can be picked out. |
ReadableStream<Uint8Array<ArrayBuffer>>| Parameter | Type |
|---|---|
| start(optional) | number |
| end(optional) | number |
| contentType(optional) | string |
The slice() method of the Blob interface creates and returns a new Blob object which contains data from a subset of the blob on which it's called.
BlobThe stream() method of the Blob interface returns a ReadableStream which upon reading returns the data contained within the Blob.
ReadableStream<Uint8Array<ArrayBuffer>>Retrieves text from the file.
Promise<string>A promise that resolves with the contents of the file as string.
Retrieves text from the file.
stringThe contents of the file as string.
WritableStream<Uint8Array>| Parameter | Type | Description |
|---|---|---|
| content | string | Uint8Array | The content to write into the file. |
Writes content to the file.
voidFileHandle Properties
unionA property that indicates the current byte offset in the file. Calling readBytes or writeBytes will read or write a specified amount of bytes starting from this offset. The offset is incremented by the number of bytes read or written.
The offset can be set to any value within the file size. If the offset is set to a value greater than the file size, the next write operation will append data to the end of the file.
Null if the file handle is closed.
Acceptable values are: null | number
FileHandle Methods
Closes the file handle. This allows the file to be deleted, moved or read by a different process. Subsequent calls to readBytes or writeBytes will throw an error.
void| Parameter | Type | Description |
|---|---|---|
| length | number | The number of bytes to read. |
Reads the specified amount of bytes from the file at the current offset.
Uint8Array<ArrayBuffer>| Parameter | Type | Description |
|---|---|---|
| bytes | Uint8Array | A |
Writes the specified bytes to the file at the current offset.
voidType: Class extends PathUtilities
Paths Properties
Record<string, Directory>numberA property that represents the available space on device's internal storage, represented in bytes.
DirectoryA property containing the bundle directory – the directory where assets bundled with the application are stored.
DirectoryA property containing the cache directory – a place to store files that can be deleted by the system when the device runs low on storage.
DirectoryA property containing the document directory – a place to store files that are safe from being deleted by the system.
Paths Methods
| Parameter | Type | Description |
|---|---|---|
| path | string | File | Directory | The path to get the base name from. |
| ext(optional) | string | An optional file extension. |
Returns the base name of a path.
stringA string representing the base name.
Returns the directory name of a path.
stringA string representing the directory name.
Returns the extension of a path.
stringA string representing the extension.
| Parameter | Type |
|---|---|
| ...uris | string[] |
Returns an object that indicates if the specified path represents a directory.
PathInfoChecks if a path is absolute.
booleantrue if the path is absolute, false otherwise.
Joins path segments into a single path.
stringA string representing the joined path.
Normalizes a path.
stringA string representing the normalized path.
Parses a path into its components.
{
base: string,
dir: string,
ext: string,
name: string,
root: string
}An object containing the parsed path components.
Methods
Deprecated Use
new File().copy()or import this method fromexpo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| options | RelocatingOptions |
Promise<void>Deprecated Import this method from
expo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| uri | string |
| fileUri | string |
| options(optional) | DownloadOptions |
| callback(optional) | FileSystemNetworkTaskProgressCallback<DownloadProgressData> |
| resumeData(optional) | string |
anyDeprecated Import this method from
expo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| url | string |
| fileUri | string |
| options(optional) | FileSystemUploadOptions |
| callback(optional) | FileSystemNetworkTaskProgressCallback<UploadProgressData> |
anyDeprecated Use
new File().delete()ornew Directory().delete()or import this method fromexpo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| fileUri | string |
| options(optional) | DeletingOptions |
Promise<void>Deprecated Use
File.downloadFileAsyncor import this method fromexpo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| uri | string |
| fileUri | string |
| options(optional) | DownloadOptions |
Promise<FileSystemDownloadResult>Deprecated Import this method from
expo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| fileUri | string |
Promise<string>Deprecated Use
Paths.availableDiskSpaceor import this method fromexpo-file-system/legacy. This method will throw in runtime.
Promise<number>Deprecated Use
new File().infoor import this method fromexpo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| fileUri | string |
| options(optional) | InfoOptions |
Deprecated Use
Paths.totalDiskSpaceor import this method fromexpo-file-system/legacy. This method will throw in runtime.
Promise<number>Deprecated Use
new Directory().create()or import this method fromexpo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| fileUri | string |
| options(optional) | MakeDirectoryOptions |
Promise<void>Deprecated Use
new File().move()or import this method fromexpo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| options | RelocatingOptions |
Promise<void>Deprecated Use
new File().text()or import this method fromexpo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| fileUri | string |
| options(optional) | ReadingOptions |
Promise<string>Deprecated Use
new Directory().list()or import this method fromexpo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| fileUri | string |
Promise<string[]>Deprecated Use
@expo/fetchor import this method fromexpo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| url | string |
| fileUri | string |
| options(optional) | FileSystemUploadOptions |
Promise<FileSystemUploadResult>Deprecated Use
new File().write()or import this method fromexpo-file-system/legacy. This method will throw in runtime.
| Parameter | Type |
|---|---|
| fileUri | string |
| contents | string |
| options(optional) | WritingOptions |
Promise<void>Types
| Property | Type | Description |
|---|---|---|
| idempotent(optional) | boolean | This flag controls whether the If Default: false |
| intermediates(optional) | boolean | Whether to create intermediate directories if they do not exist. Default: false |
| overwrite(optional) | boolean | Whether to overwrite the directory if it exists. Default: false |
| Property | Type | Description |
|---|---|---|
| creationTime(optional) | number | A creation time of the directory expressed in milliseconds since epoch. Returns null if the Android version is earlier than API 26. |
| exists | boolean | Indicates whether the directory exists. |
| files(optional) | string[] | A list of file names contained within a directory. |
| modificationTime(optional) | number | The last modification time of the directory expressed in milliseconds since epoch. |
| size(optional) | number | The size of the file in bytes. |
| uri(optional) | string | A |
| Property | Type | Description |
|---|---|---|
| headers(optional) | undefined | The headers to send with the request. |
| idempotent(optional) | boolean | This flag controls whether the If Default: false |
| Property | Type | Description |
|---|---|---|
| intermediates(optional) | boolean | Whether to create intermediate directories if they do not exist. Default: false |
| overwrite(optional) | boolean | Whether to overwrite the file if it exists. Default: false |
| Property | Type | Description |
|---|---|---|
| creationTime(optional) | number | A creation time of the file expressed in milliseconds since epoch. Returns null if the Android version is earlier than API 26. |
| exists | boolean | Indicates whether the file exists. |
| md5(optional) | string | Present if the |
| modificationTime(optional) | number | The last modification time of the file expressed in milliseconds since epoch. |
| size(optional) | number | The size of the file in bytes. |
| uri(optional) | string | A |
| Property | Type | Description |
|---|---|---|
| md5(optional) | boolean | Whether to return the MD5 hash of the file. Default: false |
| Property | Type | Description |
|---|---|---|
| exists | boolean | Indicates whether the path exists. Returns true if it exists; false if the path does not exist or if there is no read permission. |
| isDirectory | boolean | null | Indicates whether the path is a directory. Returns true or false if the path exists; otherwise, returns null. |
Expo 文件系统