url coming back from firebase storage is nil Swift4 - ios

Question

I'm trying to upload an image to firebase storage and get the download url to save it in database, but I get a nil value and the function returns upon checking it. I followed the documentation and solutions from other posts and I can't see where I'm mistaking.
The function is :
func uploadImage(completed: #escaping (Bool) -> (),_ image: UIImage ){
print(" ############## UPLOAD STARTED ###########")
// let stringURL: String?
// guard let uid = Auth.auth().currentUser?.uid else {return} // use the userUid to sign the alert
// Create a root reference
let storageRef = Storage.storage().reference()
// Create a reference to "mountains.jpg"
// let alertsRef = storageRef.child("userAlertImages.jpg")//("user/\(uid)") // change path for userAlertImages path
// Create a reference to 'images/mountains.jpg'
let alertsImagesRef = storageRef.child("Alert Images/userAlertImages.jpg")
// While the file names are the same, the references point to different files
// alertsRef.name == alertsImagesRef.name; // true
// alertsRef.fullPath == alertsImagesRef.fullPath; // false
let imageData = UIImageJPEGRepresentation(image, 0.5)
let metaData = StorageMetadata()
metaData.contentType = " jpeg " // data type
metaData.customMetadata = ["k1": "",
"k2" : " ",
"k3" : "",
"k4" : ""]
alertsImagesRef.putData(imageData! as Data , metadata: metaData) { metaData, error in
if(error != nil){
print(error as Any)
return
}
}
// Fetch the download URL
alertsImagesRef.downloadURL { (url,error) in
guard let downloadURL = url else {
print("########## downloaded url is: \(url) #############")
return
}
NewMapViewController.alertImageURL = (url?.absoluteString) ?? ""
// NewMapViewController.alertImageURL = (downloadURL)
print("######### url is:\(String(describing: url)) #########")
completed(true)
// self.postAlertNotification()
self.tapCounter = 0
self.performSegue(withIdentifier: "chooseIconSegue", sender: self)
}
}
can you see where's the error?
Many thanks.

Answer 1

Thinking about it I realised that downloadURL fetch was actually done before than the image upload was complete, that's because Firebase is asynchronous. So I added a completion block to the uploading part, and in the completion scope I put the downloadURL fetching part.
It's not blinking eyes fast and I will appreciate any suggestion on speeding up things, because this way there is a little lag before the seguegets performed.
It's not annoying at all an I could, and probably should, add a little spinning wheel to show users that the app has not frozen, but I rather just avoid the lag altogether if possible. I left the prints written in hope that this post will help others new to Firebase as I am, giving detailed almost step-by-step guidance, as this kind of answers really helped me before, and I haven't found any on the subject.
Rewritten function is:
func uploadImage(completed: #escaping (Bool) -> (),_ image: UIImage ){
print(" ############## UPLOAD STARTED ###########")
// Create a root reference
let storageRef = Storage.storage().reference()
// Create a reference to Images folder
let alertsImagesRef = storageRef.child("Alert Images")
// Create a reference for new images
let uuid = UUID()
let imageRef = alertsImagesRef.child("userAlertImage \(uuid).jpg")
let imageData = UIImageJPEGRepresentation(image, 0.5)
let metaData = StorageMetadata()
metaData.contentType = " jpeg " // data type
metaData.customMetadata = ["k1": "",
"k2" : " ",
"k3" : "",
"k4" : ""]
imageRef.putData(imageData! as Data , metadata: metaData, completion: { metaData, error in
if(error != nil){
print(error as Any)
return
}
print(" ####### image uploaded #######")
self.tapCounter = 0
self.performSegue(withIdentifier: "chooseIconSegue", sender: self)
// fetch url v2
imageRef.downloadURL(completion: { (url, err) in
if let err = err {
print("Error downloading image file, \(err.localizedDescription)")
return
}
guard let url = url else { return }
//Now you have the download URL for the image, and can do whatever you want with it.
NewMapViewController.alertImageURL = url.absoluteString
print(" ######### url is:\(String(describing: url)) #########")
completed(true)
// self.postAlertNotification()
// self.tapCounter = 0
// self.performSegue(withIdentifier: "chooseIconSegue", sender: self)
print(" ############## UPLOAD ENDED ###########")
})
})
}