如何等待 React Native Image Picker 回调函数响应？

Question

我想制作一个功能，将从 react-native-image-picker 中选取的照片上传到 firestore，然后 returns 上传图像的 URL 的值。照片上传成功，我可以在控制台打印下载 URL，问题是当我尝试 return 时，函数中的 URL 是未定义的。我尝试使用异步函数等待图像选择器响应在我 return 它的值之前完成，但它仍然 returns {"_U": 0, "_V": 0, "_W" : 空, "_X": 空}.

uploadImg: async () =>{
        await ImagePicker.launchImageLibrary({ mediaType: 'photo' }, response => {
            if (response.error) {
                alert('Something went wrong');
            } else {
                try {
                    const { path, uri } = response;
                    const fileSource = Platform.OS === 'android' ? uri : path;
                    const { fileName } = response;
                    const storageRef = storage().ref(fileName);
                    
                    storageRef.putFile(fileSource).on('state_changed', snapshot => {
                        switch (snapshot.state) {
                            case 'running':
                                setImageURI(null);
                                break;
                            case 'success':
                                snapshot.ref.getDownloadURL().then(downloadURL => {
                                    setImageURI(downloadURL);
                                    //This console log works, and actually prints the correct url
                                    console.log(`Download URL ${downloadURL}`); 
                                });
                                break;
                            default:
                                break;
                        }
                        
                    });
                } catch (error) {
                    console.log(error)
                }
            }
        }); 
        return imageURI;
    }

我很确定问题不在于状态、上传图片或图像选择器响应。这可能是异步函数的错误使用。

Answer 1

async/await 的一个非常基本的用法是这样的：

const someCuteAsyncFunc = async () => {
  try {
    let promise = new Promise((resolve, reject) => {
       setTimeout(() => resolve("done!"), 1000)
    });

    let result = await promise; // wait until the promise resolves (*)

    alert(result); // "done!"
  } catch (error) {
    console.error(error);
  }
}

基于this example.

鉴于您的代码，try/catch、if/else、开关和最后的 return，我认为您需要先简化函数以确保您 return 诺言中的图像。关于这个话题有一个很好的答案。

Answer 2

这是因为您在 firebase 调用完成执行之前从您的函数返回。我对您的代码进行了一些更新，以便函数可以等待 firebase 响应。

uploadToFirebase: ( fileName, filesource )=>new Promise((resolve, reject)=>{
  const storageRef = storage().ref(fileName);
  storageRef.putFile(fileSource).on('state_changed', snapshot => {
    switch (snapshot.state) {
      case 'running':
        setImageURI(null);
        break;
      case 'success':
        snapshot.ref.getDownloadURL().then(downloadURL => {
          setImageURI(downloadURL);
          //This console log works, and actually prints the correct url
          console.log(`Download URL ${downloadURL}`); 
        });
        break;
      default:
        break;
    }
    resolve();
  });
})

uploadImg: async () =>{
  let response = await ImagePicker.launchImageLibraryAsync({ mediaType: 'photo' });
  if (response.error) {
    alert('Something went wrong');
  } else {
    const { path, uri } = response;
    const fileSource = Platform.OS === 'android' ? uri : path;
    const { fileName } = response;
    await uploadToFirebase(fileName, fileSource)
  }
  return imageURI;
}

如何等待 React Native Image Picker 回调函数响应？

How to await for the react native Image Picker callback function response?

javascript

react-native

asynchronous

google-cloud-firestore

react-native-image-picker