Reload TableView data only after downloading everything from the firebase database Swift - swift

Question

I have been searching for a while now, but I don't know how to deal with this problem.
I have a Firebase Database with some data and the links to images stored into the Storage.
I want my UICollectionView to be reloaded after I downloaded every single image from the database, and not only the first one.
newRef.observeSingleEvent(of: .value, with: { (snapshotOne) in
for child in snapshotOne.children {
let snap = child as! DataSnapshot
let key = snap.key
newRef.child(key).observeSingleEvent(of: .value, with: { (snapshotTwo) in
for child in snapshotTwo.children {
let snappotto = child as! DataSnapshot
var imageDownloaded: UIImage?
if let dictionary = snappotto.value as? [String : AnyObject] {
let url = URL(string: dictionary["imageURL"] as! String)
URLSession.shared.dataTask(with: url!) { (data, response, error) in
if error != nil {
print("[Error]: \(String(describing: error))")
return
}
imageDownloaded = UIImage(data: data!)
let person = Person(name: dictionary["name"] as! String, surname: dictionary["surname"] as! String, tags: [.castana], image: imageDownloaded!)
self.storedData.append(person)
self.filteredData = self.storedData
DispatchQueue.main.sync {
UIApplication.shared.endIgnoringInteractionEvents()
self.collectionView.reloadData()
self.dismiss(animated: false, completion: nil)
}
}.resume()
}
}
}) { (error) in
print("[Error]: \(String(describing: error))")
}
}
}) { (error) in
print("[Error]: \(error)")
}
This is the code I use, but this updates my UICollectionView after only the first image is downloaded, and with that it endsIgnoringInteractionEvents - and allows the user to reload the data again and again and this causes a lot of images to duplicate.
How can I move the reloading and the endIgnoringInteractionEvents after every single item from my database is downloaded?
The database is structured like this:
| folder
-| user
--| autoId
---| name
---| surname
---| imageUrl
--|autoId
---| name
---| surname
---| imageUrl
-| user
--| autoId
---| name
---| surname
---| imageUrl
Thanks a lot, NicopDev

Answer 1

You're nesting observers on nested data, which seems like a waste of code. When you attach an observer to a location, all data under that location is loaded already.
So you can just loop over the nested snapshot to get the same result:
newRef.observeSingleEvent(of: .value, with: { (snapshot) in
for child in snapshot.children {
let userSnapshot = child as! DataSnapshot
let userKey = userSnapshot.key
for child in userSnapshot.children {
let imageSnapshot = child as! DataSnapshot
var imageDownloaded: UIImage?
...
With that out of the way, let's move on to your real question: how can you detect when all images have loaded.
One simple, cross-platform way to do this is by simply counting how many images you have loaded, and compare that to how many images you know exist. Since you have a tree of only existing images, you can do both in a iteration over the double nested structure
let knownImageCount = 0 // we start with no knowledge of any image
let loadedImageCount = 0 // we also haven't loaded any image yet
for child in snapshot.children {
let userSnapshot = child as! DataSnapshot
let userKey = userSnapshot.key
knownImageCount = knownImageCount + userSnapshot.childrenCount // we've found out about N more images
for child in userSnapshot.children {
let imageSnapshot = child as! DataSnapshot
var imageDownloaded: UIImage?
...
URLSession.shared.dataTask(with: url!) { (data, response, error) in
...
loadedImageCount = loadedImageCount + 1 // we loaded an additional image
if loadedImageCount == knownImageCount {
... // we've loaded all known images, we're done!
}
}.resume()