Async Future Promise not working in Swift 5 - swift

Question

I'm trying to implement an async call to a function loadUserFromFirebase and populate and return an array based on user attributes that I then use to write to a firebase collection.
I'm trying to use the Combine framework from Swift using future and promises but for some reason, the receiveCompletion and receiveValue don't get called and thus I get an empty array from my async function call.
Here is my code:
var cancellable = Set<AnyCancellable>()
func loadUserFromFirebase(groupUserIds: [String], handler: #escaping ([groupMate]) -> Void) {
var groupmateID = 0
var groupMates : [groupMate] = []
print("groupUserIds: \(groupUserIds)" )
for groupUserUID in groupUserIds {
print("groupUserUID: \(groupUserUID)" )
let future = Future<groupMate, Never> { promise in
self.ref.collection("Users").document(groupUserUID).getDocument(){
(friendDocument, err) in
if let err = err {
print("Error getting documents \(err)")
} else {
// print("friendDocument: \(String(describing: friendDocument?.data()))" )
let groupUsername = (friendDocument?.data()?["username"]) as! String
let groupUID = (friendDocument?.data()?["uid"]) as! String
let groupName = (friendDocument?.data()?["name"]) as! String
let groupPic = (friendDocument?.data()?["imageurl"]) as! String
promise(.success(groupMate(id: groupmateID, uid: groupUID , name: groupName , username: groupUsername, pic: groupPic)))
}
groupmateID += 1
}
}
print("in receiveCompletion")
future.sink(receiveCompletion: { completion in
print("in receiveCompletion")
print(1, completion)
switch completion {
case .failure(let error):
print(3, error)
handler([])
return
case .finished:
break
}
},
receiveValue: {
print("in receiveValue")
groupMates.append($0)
print(groupMates)
handler(groupMates)
}).store(in: &cancellable)
}
}
func creategroup(groupName: String){
addedTogroupUsers.append(self.uid)
print("here111")
loadUserFromFirebase(groupUserIds: addedTogroupUsers) { groupMates in
print("here222")
let groupData: [String: Any] = [
"groupName": "\(groupName)",
"groupmates": groupMates
]
print("here333 \(groupData)")
print("groupMates are \(self.groupMates)")
var groupref: DocumentReference? = nil
groupref = self.ref.collection("groups").addDocument(data: groupData) { err in
if let err = err {
print("Error adding document: \(err)")
} else {
print("Document added with ID: \(groupref!.documentID)")
for addedgroupUser in self.addedTogroupUsers {
self.ref.collection("Users").document(addedgroupUser).updateData([
"groups": FieldValue.arrayUnion([groupref!.documentID])
])
}
}
}
print("groupName is \(groupName) and addedTogroup are \(self.addedTogroupUsers)")
}
}
I'm trying to see if AnyCancellable is the way to go but since I'm using a chained array of future promises, I'm not sure how to implement it. Please let me know how you'd solve this problem so that the array does get populated since the documents do exist and the print inside the method call work but the groupMates array in the createGroup function prints an empty array afterwards. Thanks!
Edit: Added AnyCancallable to Code along with completion handler as suggested

Answer 1

dealing with async functions can be tricky. You are getting an empty array, because you are returning too early, in loadUserFromFirebase. Try this approach (untested) using the old style closure:
func loadUserFromFirebase(groupUserIds: [String], handler: #escaping ([groupMate]) -> Void) { // <-- here
var groupmateID = 0
var groupMates : [String] = []
print("groupUserIds: \(groupUserIds)" )
for groupUserUID in groupUserIds {
print("groupUserUID: \(groupUserUID)" )
let future = Future<groupMate, Never> { promise in
self.ref.collection("Users").document(groupUserUID).getDocument(){ (friendDocument, err) in
if let err = err {
print("Error getting documents \(err)")
} else {
print("friendDocument: \(String(describing: friendDocument?.data()))" )
let groupUsername = (friendDocument?.data()?["username"]) as! String
let groupUID = (friendDocument?.data()?["uid"]) as! String
let groupName = (friendDocument?.data()?["name"]) as! String
let groupPic = (friendDocument?.data()?["imageurl"]) as! String
promise(.success(groupMate(id: groupmateID, uid: groupUID , name: groupName , username: groupUsername, pic: groupPic)))
}
groupmateID += 1
}
}
future.sink(receiveCompletion: { completion in
print("in receiveCompletion")
print(1, completion)
switch completion {
case .failure(let error):
print(3, error)
handler([]) // <-- here
return // <-- here
case .finished:
break
}
},
receiveValue: {
print("in receiveValue")
groupMates.append($0)
print(groupMates)
handler(groupMates) // <-- here
})
}
// <-- do not return here
}
func creategroup(groupName: String) {
addedTogroupUsers.append(self.uid)
// -- here wait until you get the data
loadUserFromFirebase(groupUserIds: addedTogroupUsers) { groupMates in
let groupData: [String: Any] = [
"groupName": "\(groupName)",
"groupmates": groupMates // <-- here
]
print("groupMates are \(self.groupMates)")
var groupref: DocumentReference? = nil
groupref = ref.collection("groups").addDocument(data: groupData) { err in
if let err = err {
print("Error adding document: \(err)")
} else {
print("Document added with ID: \(groupref!.documentID)")
for addedgroupUser in self.addedTogroupUsers {
self.ref.collection("Users").document(addedgroupUser).updateData([
"groups": FieldValue.arrayUnion([groupref!.documentID])
])
}
}
}
print("groupName is \(groupName) and addedTogroup are \(addedTogroupUsers)")
}
}
Note, if you are targeting ios 15, macos 12, you are far better served if you use the swift 5.5 async/await/task features. They really work well.
EDIT: trying to return all results
func loadUserFromFirebase(groupUserIds: [String], handler: #escaping ([groupMate]) -> Void) {
var groupmateID = 0
var groupMates : [String] = []
print("groupUserIds: \(groupUserIds)" )
var arr: [Future<groupMate, Never>] = [Future<groupMate, Never>]()
var cancellable = Set<AnyCancellable>()
for groupUserUID in groupUserIds {
print("groupUserUID: \(groupUserUID)" )
let future = Future<groupMate, Never> { promise in
self.ref.collection("Users").document(groupUserUID).getDocument(){ (friendDocument, err) in
if let err = err {
print("Error getting documents \(err)")
} else {
print("friendDocument: \(String(describing: friendDocument?.data()))" )
let groupUsername = (friendDocument?.data()?["username"]) as! String
let groupUID = (friendDocument?.data()?["uid"]) as! String
let groupName = (friendDocument?.data()?["name"]) as! String
let groupPic = (friendDocument?.data()?["imageurl"]) as! String
promise(.success(groupMate(id: groupmateID, uid: groupUID , name: groupName , username: groupUsername, pic: groupPic)))
}
groupmateID += 1
}
}
arr.append(future)
}
Publishers.MergeMany(arr)
.collect()
.sink { _ in
print("-----> merging ")
} receiveValue: { value in
print("-----> value: \(value)")
groupMates = value // <--- maybe append?
print(groupMates)
handler(groupMates)
}
.store(in: &cancellable)
}