可能未处理的 Promise Rejection (id:0) TypeError: undefined is not an object (evalating 'ImagePicker.Permissions.askAsync)答案

【问题标题】：Possible Unhandled Promise Rejection (id:0) TypeError: undefined is not an object (evaluating 'ImagePicker.Permissions.askAsync)可能未处理的 Promise Rejection (id:0) TypeError: undefined is not an object (evalating 'ImagePicker.Permissions.askAsync)
【发布时间】：2020-12-22 17:48:59
【问题描述】：

我正在使用 React-Native 和 Expo 构建一个 iOS 应用程序。我已经弄清楚如何访问用户的照片库，但无法从他们的设备请求权限。相反，它只是在不询问的情况下访问相机胶卷，这在 iOS 中显然是不允许的。以下是我的一些代码：

    import React, {useState, useEffect, useRef} from 'react';
    import * as ImagePicker from 'expo-image-picker';
    import Permissions, {usePermissions} from 'expo-permissions';
    import Constants from 'expo-constants'

//useEffect函数是检查异步函数是否被接受时运行的函数

const Screen = ({navigation}) => {

const [ imagePicker1, setImagePicker1 ] = useState(null);

useEffect(() => {
    const permission_get1 = async ()=> {
        if (Platform.OS !== 'web'){
            let { status } = await ImagePicker.Permissions.askAsync(Permissions.MEDIA_LIBRARY);
            if (status !== 'granted'){
                console.log('No permission given')
                alert('Camera roll required for to upload photo from your library');
                return;
            }
            /*if (status === 'granted'){
                console.log('Permission granted')*/

            let imagePicker1 = await ImagePicker.getMediaLibraryAsync()
                setImagePicker1(imagePicker1)
                console.log('It worked')
            }

    };
            permission_get1();
}, []);

【问题讨论】：

标签： react-native expo typeerror ios-permissions expo-permissions

【解决方案1】：

我最终用这个来让它工作：我相信前面的例子使用的是一种折旧的方法。

 import * as ImagePicker from 'expo-image-picker'

const pickImage = async ()=>{
  const { granted } = await Permissions.askAsync(Permissions.CAMERA_ROLL)
  if(granted){
    console.log('access granted')
    let data = await ImagePicker.launchImageLibraryAsync({
      mediaTypes:ImagePicker.MediaTypeOptions.Images,
      allowsEditing: true,
      aspect:[1,1],
      quality:0.5,
    })
    console.log(data)

    if (!data.cancelled){
    setImage(data.uri);
  }
  
  }else{
    Alert.alert('Permissions required to access camera roll.')
  }

}

【讨论】：