如何压缩刚用 React Native Expo 拍摄的图片答案

【问题标题】：How to compress picture just taken with React Native Expo如何压缩刚用 React Native Expo 拍摄的图片
【发布时间】：2020-05-16 17:05:00
【问题描述】：

我正在使用 expo 和 MediaLibrary 中的 Camera 组件来保存拍摄的照片。我的问题是，在画廊中使用 MediaLibrary 保存该图像时如何压缩该图像？我正在尝试压缩它，因为稍后我还将将该图像上传到 Firebase 存储。到目前为止，这是我现在没有压缩的代码：

import React, { useState, useEffect} from 'react';
import { Text, View, TouchableOpacity } from 'react-native';
import { Camera } from 'expo-camera';
import * as MediaLibrary from 'expo-media-library';
import { Dimensions } from 'react-native';
const {height, width} = Dimensions.get('window');

export default function App() {

  const [hasPermission, setHasPermission] = useState(null);
  const [cameraRef, setCameraRef] = useState(null)
  const [type, setType] = useState(Camera.Constants.Type.back);
  useEffect(() => {
    (async () => {
      const { status } = await Camera.requestPermissionsAsync();
      MediaLibrary.requestPermissionsAsync();
      setHasPermission(status === 'granted');
    })();
  }, []);

  if (hasPermission === null) {
    return <View />;
  }

  if (hasPermission === false) {
    return <Text>No access to camera</Text>;
  }

  return (
    <View style={{ flex: 1 }}>
      <Camera style={{ flex: 1 }} type={type} ref={ref => {
        setCameraRef(ref) ;
      }}>
        <View
          style={{
            flex: 1,
            backgroundColor: 'transparent',
            justifyContent: 'flex-end'
          }}>
          <TouchableOpacity style={{alignSelf: 'center', marginBottom: 20}} onPress={async() => {
            if(cameraRef){
              let photo = await cameraRef.takePictureAsync({ skipProcessing: true });
              MediaLibrary.saveToLibraryAsync(photo.uri);
            }
          }}>
            <View style={{ 
              borderWidth: 2,
              borderColor: 'white',
              height: 50,
              width:50,
              display: 'flex',
              justifyContent: 'center',
              alignItems: 'center',
              borderRadius: 25,
              }}
            >
              <View style={{
                borderWidth: 2,
                borderColor: 'white',
                height: 40,
                width:40,
                backgroundColor: 'white',
                borderRadius: 25}} >
              </View>
            </View>
          </TouchableOpacity>
        </View>
      </Camera>
    </View>
  );
}

【问题讨论】：

标签： react-native camera compression expo media-library

【解决方案1】：

ImageManipulator 自带 expo，你可以压缩、调整大小、旋转、裁剪等等。

import { ImageManipulator } from 'expo';

const manipResult = await ImageManipulator.manipulate(
    imageUri,
    [{ resize: { width: 640, height: 480 } }],
    { format: 'jpg' }
);

结帐https://docs.expo.io/versions/latest/sdk/imagemanipulator/

【讨论】：

【解决方案2】：

ImageManipulator 已移至 expo-image-manipulator 包。更新您的示例：

import React, { useState, useEffect } from 'react';
import { Text, View, TouchableOpacity } from 'react-native';
import { Camera } from 'expo-camera';
import * as MediaLibrary from 'expo-media-library';
import { Dimensions } from 'react-native';

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

const {height, width} = Dimensions.get('window');

export default function App() {

  // Same code as before

  return (
    <View style={{ flex: 1 }}>
      <Camera style={{ flex: 1 }} type={type} ref={ref => {
        setCameraRef(ref);
      }}>
        <View
          style={{
            flex: 1,
            backgroundColor: 'transparent',
            justifyContent: 'flex-end'
          }}>
          <TouchableOpacity style={{alignSelf: 'center', marginBottom: 20}} onPress={async() => {
            if(cameraRef) {
              let photo = await cameraRef.takePictureAsync({ skipProcessing: true });
              // New code here
              const manipResult = await ImageManipulator.manipulateAsync(
                photo.uri,
                [{ rotate: 90 }, { flip: ImageManipulator.FlipType.Vertical }],
                { compress: 1, format: ImageManipulator.SaveFormat.PNG }
          );
              MediaLibrary.saveToLibraryAsync(manipResult.uri);
            }
          }}>
            <View style={{ /* Same style properties here */ }}
              >
              </View>
            </View>
          </TouchableOpacity>
        </View>
      </Camera>
    </View>
  );
}

More details here.

【讨论】：