Expo ImageManipulator

提供用于在本地文件系统上进行图片操作的 API 的库。

Android

iOS

Web

Bundled version:

~13.1.7

expo-image-manipulator 提供了一个 API 来修改存储在本地文件系统上的图片。

¥expo-image-manipulator provides an API to modify images stored on the local file system.

安装

¥Installation

Terminal

- npx expo install expo-image-manipulator

If you are installing this in an existing React Native app, make sure to install expo in your project.

用法

¥Usage

这将首先将图片顺时针旋转 90 度，然后垂直翻转旋转的图片并将其另存为 PNG。

¥This will first rotate the image 90 degrees clockwise, then flip the rotated image vertically and save it as a PNG.

Basic ImageManipulator usage

import { useState } from 'react';
import { Button, Image, StyleSheet, View } from 'react-native';
import { Asset } from 'expo-asset';
import { FlipType, SaveFormat, useImageManipulator } from 'expo-image-manipulator';

const IMAGE = Asset.fromModule(require('./assets/snack-icon.png'));

export default function App() {
const [image, setImage] = useState(IMAGE);
const context = useImageManipulator(IMAGE.uri);

const rotate90andFlip = async () => {
  context.rotate(90).flip(FlipType.Vertical);
  const image = await context.renderAsync();
  const result = await image.saveAsync({
    format: SaveFormat.PNG,
  });

  setImage(result);
};

return (
  <View style={styles.container}>
    <View style={styles.imageContainer}>
      <Image source={{ uri: image.localUri || image.uri }} style={styles.image} />
    </View>
    <Button title="Rotate and Flip" onPress={rotate90andFlip} />
  </View>
);
}

const styles = StyleSheet.create({
container: {
  flex: 1,
  justifyContent: 'center',
},
imageContainer: {
  marginVertical: 20,
  alignItems: 'center',
  justifyContent: 'center',
},
image: {
  width: 300,
  height: 300,
  resizeMode: 'contain',
},
});

API

import * as ImageManipulator from 'expo-image-manipulator';

Constants

`ImageManipulator.ImageManipulator`

Type: ImageManipulator

Hooks

`useImageManipulator(source)`

Parameter	Type
source	`string \| SharedRef<'image'>`

Returns:

ImageManipulatorContext

Classes

`ImageManipulator`

Type: Class extends _default

ImageManipulator Methods

`manipulate(source)`

Parameter	Type
source	`string \| SharedRef<'image'>`

Loads an image from the given URI and creates a new image manipulation context.

Returns:

ImageManipulatorContext

`ImageManipulatorContext`

Type: Class extends SharedObject

A context for an image manipulation. It provides synchronous, chainable functions that schedule transformations on the original image to the background thread. Use an asynchronous renderAsync to await for all transformations to finish and access the final image.

ImageManipulatorContext Methods

`crop(rect)`

Parameter	Type	Description
rect	`{ height: number, originX: number, originY: number, width: number }`	Fields specify top-left corner and dimensions of a crop rectangle.

Crops the image to the given rectangle's origin and size.

Returns:

ImageManipulatorContext

`extent(options)`

Only for:

Web

Parameter	Type
options	`{ backgroundColor: null \| string, height: number, originX: number, originY: number, width: number }`

Set the image size and offset. If the image is enlarged, unfilled areas are set to the backgroundColor. To position the image, use originX and originY.

Returns:

ImageManipulatorContext

`flip(flipType)`

Parameter	Type	Description
flipType	`'vertical' \| 'horizontal'`	An axis on which image will be flipped. Only one flip per transformation is available. If you want to flip according to both axes then provide two separate transformations.

Flips the image vertically or horizontally.

Returns:

ImageManipulatorContext

`renderAsync()`

Awaits for all manipulation tasks to finish and resolves with a reference to the resulted native image.

Returns:

Promise<ImageRef>

`reset()`

Resets the manipulator context to the originally loaded image.

Returns:

ImageManipulatorContext

`resize(size)`

Parameter	Type	Description
size	`{ height: null \| number, width: null \| number }`	Values correspond to the result image dimensions. If you specify only one value, the other will be calculated automatically to preserve image ratio.

Resizes the image to the given size.

Returns:

ImageManipulatorContext

`rotate(degrees)`

Parameter	Type	Description
degrees	`number`	Degrees to rotate the image. Rotation is clockwise when the value is positive and counter-clockwise when negative.

Rotates the image by the given number of degrees.

Returns:

ImageManipulatorContext

`ImageRef`

Type: Class extends SharedRef<'image'>

A reference to a native instance of the image.

ImageRef Properties

`height`

Type: number

Height of the image.

`nativeRefType`

Type: string

The type of the native reference.

`width`

Type: number

Width of the image.

ImageRef Methods

`saveAsync(options)`

Parameter	Type	Description
options(optional)	`SaveOptions`	A map defining how modified image should be saved.

Saves the image to the file system in the cache directory.

Returns:

Promise<ImageResult>

Methods

Deprecated It has been replaced by the new, contextual and object-oriented API. Use ImageManipulator.manipulate or useImageManipulator instead.

`ImageManipulator.manipulateAsync(uri, actions, saveOptions)`

Parameter	Type	Description
uri	`string`	URI of the file to manipulate. Should be on the local file system or a base64 data URI.
actions(optional)	`Action[]`	An array of objects representing manipulation options. Each object should have only one of the keys that corresponds to specific transformation. Default:`[]`
saveOptions(optional)	`SaveOptions`	A map defining how modified image should be saved. Default:`{}`

Manipulate the image provided via uri. Available modifications are rotating, flipping (mirroring), resizing and cropping. Each invocation results in a new file. With one invocation you can provide a set of actions to perform over the image. Overwriting the source file would not have an effect in displaying the result as images are cached.

Returns:

Promise<ImageResult>

Promise which fulfils with ImageResult object.

Types

`Action`

Literal Type: union

Acceptable values are: ActionResize | ActionRotate | ActionFlip | ActionCrop | ActionExtent

`ActionCrop`

Property	Type	Description
crop	`{ height: number, originX: number, originY: number, width: number }`	Fields specify top-left corner and dimensions of a crop rectangle.

`ActionExtent`

Property	Type	Description
extent	`{ backgroundColor: string \| null, height: number, originX: number, originY: number, width: number }`	Only for: Web Set the image size and offset. If the image is enlarged, unfilled areas are set to the `backgroundColor`. To position the image, use `originX` and `originY`.

`ActionFlip`

Property	Type	Description
flip	`FlipType`	An axis on which image will be flipped. Only one flip per transformation is available. If you want to flip according to both axes then provide two separate transformations.

`ActionResize`

Property	Type	Description
resize	`{ height: number, width: number }`	Values correspond to the result image dimensions. If you specify only one value, the other will be calculated automatically to preserve image ratio.

`ActionRotate`

Property	Type	Description
rotate	`number`	Degrees to rotate the image. Rotation is clockwise when the value is positive and counter-clockwise when negative.

`ImageResult`

Property	Type	Description
base64(optional)	`string`	It is included if the `base64` save option was truthy, and is a string containing the JPEG/PNG (depending on `format`) data of the image in Base64. Prepend that with `'data:image/xxx;base64,'` to get a data URI, which you can use as the source for an `Image` element for example (where `xxx` is `jpeg` or `png`).
height	`number`	Height of the image or video.
uri	`string`	An URI to the modified image (usable as the source for an `Image` or `Video` element).
width	`number`	Width of the image or video.

`SaveOptions`

A map defining how modified image should be saved.

Property	Type	Description
base64(optional)	`boolean`	Whether to also include the image data in Base64 format.
compress(optional)	`number`	A value in range `0.0` - `1.0` specifying compression level of the result image. `1` means no compression (highest quality) and `0` the highest compression (lowest quality).
format(optional)	`SaveFormat`	Specifies what type of compression should be used and what is the result file extension. `SaveFormat.PNG` compression is lossless but slower, `SaveFormat.JPEG` is faster but the image has visible artifacts. Defaults to `SaveFormat.JPEG`

Enums

`FlipType`

`Horizontal`

FlipType.Horizontal ＝ "horizontal"

`Vertical`

FlipType.Vertical ＝ "vertical"

`SaveFormat`

`JPEG`

SaveFormat.JPEG ＝ "jpeg"

`PNG`

SaveFormat.PNG ＝ "png"

`WEBP`

SaveFormat.WEBP ＝ "webp"