如何完成将图像上传到Firebase存储，然后将imageUrl保存到Firebase数据库

Question

I didn't find an answer that satisfied me and hope you have any idea. I want to upload my images to the Firebase storage and save the imageUrls into the Firebase database.

     var imageUrls = [String]()

     func uploadImagesToStorage(imagesArray: [UIImage]) {


    for i in imagesArray {

        guard let uploadData = UIImageJPEGRepresentation(i, 0.3) else { return }
        let fileName = NSUUID().uuidString

         FIRStorage.storage().reference().child("post_Images").child(fileName).put(uploadData, metadata: nil) { (metadata, err) in

            if let err = err {
            return
            }

            guard let profileImageUrl = metadata?.downloadURL()?.absoluteString else { return }
            self.imageUrls.append(profileImageUrl)

        }.resume()

  } //..End loop
       saveToDatabaseWithImageUrl(imageUrls: imageUrls)

Uploading the images works with the uploadImagesToStorage(imagesArray: [UIImage]) method. This method gets an array as argument which contains the images that I want to upload. While uploading the images I'm downloading the imageUrl information from the metadata that firebase is giving me and save that imageUrl into the imageUrls array. For loop is necessary to save the imageUrl information for every single image. When the images are uploaded and the imageUrls Array is filled with the imageUrl information I call the function func saveToDatabaseWithImageUrl(imageUrls: [String]) to save the imageUrls into the database. Checking Firebase I see that the images are saved into the Firebase storage, but the imageUrls are not saved into the Firebase database. While debugging my code I found out that the reason for this behavior is that while the images are uploaded the code jumps to the next line. So it calls the saveToDatabaseWithImageUrls with an empty imageUrls array. I read the [Documentation][1] and tried to manage the upload with the .resume() method. Still it jumped to the saveToDatabaseWithImageUrl method. I don't know how to guarantee that the upload is finished and then the next line of code is executed. Thanks for your help.

Answer 1

Its happen because success block of your .child("post_Images").child(fileName).put call asynchronously. Rest of code go sync. So your for start uploading photos and after that you are saving URLs to database but urls are empty because you don't wait for finish uploading.

I give you a perfect solution based on DispathGroup

//Create DispatchGroup
let fetchGroup = DispatchGroup()

for i in imagesArray {
    guard let uploadData = UIImageJPEGRepresentation(i, 0.3) else { return }

    let fileName = NSUUID().uuidString
    //Before every iteration enter to group
    fetchGroup.enter()        
    FIRStorage.storage().reference().child("post_Images").child(fileName).put(uploadData, metadata: nil) { (metadata, err) in
        if let err = err {
        fetchGroup.leave()
        return
        }

        guard let profileImageUrl = metadata?.downloadURL()?.absoluteString else { return }
        self.imageUrls.append(profileImageUrl)
        //after every completion asynchronously task leave the group
        fetchGroup.leave()
    }.resume()
}

And know id magic

fetchGroup.notify(queue: DispatchQueue.main) {
    //this code will call when number of enter of group will be equal to number of leaves from group
    //save your url here
    saveToDatabaseWithImageUrl(imageUrls: imageUrls)
}

This solution don't block a thread, everything works asynchronously here.