Handle completion with asynchronous call in for loop [duplicate] - ios

Question

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Completion gets called soon
(2 answers)
Closed 2 years ago.
I have a function that should have a completion-handler which should only be called if everything inside of it is actually completed. That is my function:
static func getWishes(dataSourceArray: [Wishlist], completion: #escaping (_ success: Bool, _ dataArray: [Wishlist]) -> Void){
var dataSourceArrayWithWishes = dataSourceArray
let db = Firestore.firestore()
let userID = Auth.auth().currentUser!.uid
for list in dataSourceArray {
db.collection("users").document(userID).collection("wishlists").document(list.name).collection("wünsche").order(by: "wishCounter").getDocuments() { ( querySnapshot, error) in
if let error = error {
print(error.localizedDescription)
completion(false, dataSourceArrayWithWishes)
} else {
// append every Wish to array at wishIDX
for document in querySnapshot!.documents {
let documentData = document.data()
let imageUrlString = document["imageUrl"] as? String ?? ""
let imageView = UIImageView()
imageView.image = UIImage()
if let imageUrl = URL(string: imageUrlString) {
let resource = ImageResource(downloadURL: imageUrl)
imageView.kf.setImage(with: resource) { (result) in
switch result {
case .success(_):
dataSourceArrayWithWishes[wishIDX].wishes.append(Wish(name: name, link: link, price: price, note: note, image: imageView.image!, checkedStatus: false))
completion(true, dataSourceArrayWithWishes)
print("success")
case .failure(_):
print("fail")
}
}
} else {
dataSourceArrayWithWishes[wishIDX].wishes.append(Wish(name: name, link: link, price: price, note: note, image: imageView.image!, checkedStatus: false))
}
}
}
}
}
}
The problem lies in imageView.kf.setImage...
Right now I am calling completion after the first .success but the function should only be completed if the for-loop and all the setImages are being finished. I've tried a couple of things now but I can not make it work. So I wonder what's best practice for this case?

Answer 1

Here is how you use DispatchGroup for this... You need DispatchGroup to get notified when the asynchronous loop is finished
static func getWishes(dataSourceArray: [Wishlist], completion: #escaping (_ success: Bool, _ dataArray: [Wishlist]) -> Void){
var dataSourceArrayWithWishes = dataSourceArray
let db = Firestore.firestore()
let userID = Auth.auth().currentUser!.uid
let group = DispatchGroup()
for list in dataSourceArray {
group.enter()
db.collection("users").document(userID).collection("wishlists").document(list.name).collection("wünsche").order(by: "wishCounter").getDocuments() { ( querySnapshot, error) in
defer{ group.leave() }
if let error = error {
print(error.localizedDescription)
completion(false, dataSourceArrayWithWishes)
} else {
// append every Wish to array at wishIDX
for document in querySnapshot!.documents {
group.enter()
let documentData = document.data()
let imageUrlString = document["imageUrl"] as? String ?? ""
let imageView = UIImageView()
imageView.image = UIImage()
if let imageUrl = URL(string: imageUrlString) {
let resource = ImageResource(downloadURL: imageUrl)
imageView.kf.setImage(with: resource) { (result) in
defer{ group.leave() }
switch result {
case .success(_):
dataSourceArrayWithWishes[wishIDX].wishes.append(Wish(name: name, link: link, price: price, note: note, image: imageView.image!, checkedStatus: false))
case .failure(_):
print("fail")
}
}
} else {
dataSourceArrayWithWishes[wishIDX].wishes.append(Wish(name: name, link: link, price: price, note: note, image: imageView.image!, checkedStatus: false))
}
}
}
}
}
group.notify(queue: DispatchQueue.main) {
completion(true, dataSourceArrayWithWishes)
print("success")
}
}