await response of image upload before continue fun

问题:

So I am working on a upload function for multiple images in an array. After a lot of struggling I have finally got my upload function to work and the images are showing up in the Firebase Database. However I have yet to find out a working way to make sure my upload function completes before continuing.

Below is the part were I am calling the upload function and try to store the response in uploadurl, the uploadurl variable is later used in the dispatch function to store the url with other data.

   try {
            uploadurl = await uploadImages()
            address = await getAddress(selectedLocation)
            console.log(uploadurl)
            if (!uploadurl.lenght) {
                Alert.alert('Upload error', 'Something went wrong uploading the photo, plase try again', [
                    { text: 'Okay' }
                ]);
                setIsLoading(true);
                return;
            }

            dispatch(

So the image upload function is below. This works to the point that the images are uploaded, however the .then call to get the DownloadURL is not started correctly and the .then images also is not working.

uploadImages = () => {
    const provider = firebase.database().ref(`providers/${uid}`);
    let imagesArray = [];
    try {
        Promise.all(photos)
            .then(photoarray => {
                console.log('all responses are resolved succesfully')
                for (let photo of photoarray) {
                    let file = photo.data;
                    const path = "Img_" + uuid.v4();
                    const ref = firebase
                        .storage()
                        .ref(`/${uid}/${path}`);
                    var metadata = {
                        contentType: 'image/jpeg',
                    };
                    ref.putString(file, 'base64', metadata).then(() => {
                        ref
                            .getDownloadURL()
                            .then(images => {
                                imagesArray.push({
                                    uri: images
                                });
                                console.log("Out-imgArray", imagesArray);

                            })
                    })
                };
                return imagesArray
            })
    } catch (e) {
        console.error(e);
    }
};

So I want to return the imagesArray, AFTER, all the photos are uploaded. So the imagesArray is then set as uploadURL in the first function? After all images URL are set in imagesArray and passed to uploadURL, only then my dispatch function to upload the rest of the data should continue. How can I make sure this is happening as expected?

I have changed this so many times now because I keep getting send to different ways of doing this that I am completely at a loss how to continue now :(

回答1:

Most of your uploadImages() code was correct, however in many places you didn't return the promise from each asynchronous action.

Quick sidestep: Handling many promises

When working with lots of asynchronous tasks based on an array, it is advised to map() the array to an array of Promises rather than use a for loop. This allows you to build an array of promises that can be fed to Promise.all() without the need to initialise and push to another array.

let arrayOfPromises = someArray.map((entry) => {
    // do something with 'entry'
    return somePromiseRelatedToEntry();
  });

Promise.all(arrayOfPromises)
  .then((resultsOfPromises) => {
    console.log('All promises resolved successfully');
  })
  .catch((err) => {
    // an error in one of the promises occurred
    console.error(err);
  })

The above snippet will fail if any of the contained promises fail. To silently ignore individual errors or defer them to handle later, you just add a catch() inside the mapped array step.

let arrayOfPromises = someArray.map((entry) => {
    // do something with 'entry'
    return somePromiseRelatedToEntry()
      .catch(err => ({hasError: true, error: err})); // silently ignore errors for processing later
  });

Updated uploadImages() code

Updating your code with these changes, gives the following result:

uploadImages = () => {
    const provider = firebase.database().ref(`providers/${uid}`);
    // CHANGED: removed 'let imagesArray = [];', no longer needed

    return Promise.all(photos) // CHANGED: return the promise chain
        .then(photoarray => {
            console.log('all responses are resolved successfully');
            // take each photo, upload it and then return it's download URL
            return Promise.all(photoarray.map((photo) => { // CHANGED: used Promise.all(someArray.map(...)) idiom
              let file = photo.data;
              const path = "Img_" + uuid.v4();
              const storageRef = firebase // CHANGED: renamed 'ref' to 'storageRef'
                    .storage()
                    .ref(`/${uid}/${path}`);
              let metadata = {
                  contentType: 'image/jpeg',
              };

              // upload current photo and get it's download URL
              return storageRef.putString(file, 'base64', metadata) // CHANGED: return the promise chain
                .then(() => {
                  console.log(`${path} was uploaded successfully.`);
                  return storageRef.getDownloadURL() // CHANGED: return the promise chain
                    .then(fileUrl => ({uri: fileUrl}));
                });
            }));
        })
        .then((imagesArray) => {                       // These lines can
          console.log("Out-imgArray: ", imagesArray)   // safely be removed.
          return imagesArray;                          // They are just
        })                                             // for logging.
        .catch((err) => {
          console.error(err);
        });
};