Find if function has finished looping firebase - ios

Question

Okay, I have been dealing with something I really need some help with, so I am here. I have a simple function where it loops through firebase and adds data to arrays. Here is the problem, I need to know where the function has finished looping. I honestly need some help figuring this out, so here is an example.
func getUsers() {
let ref = Database.database.reference()
if let myAget = self.myAgel {
ref.child("newUsers").observeSingleEvent(of: .value, with: {(snapshoter) in
if let valuer = snapshoter.value as? [String : AnyObject] {
for (one,_) in valuer {
checkCount.append("one")
ref.child("users").child(one).child("age").observeSingleEvent(of: .value, with: {(snap) in
if let agerti = snap.value as? Int {
if myAget - agerti <= 1 && myAget - agerti >= -1 {
print("Add this user")
}
}
})
}
}
print("now do something with those users")
}
})
}
}
**Console Prints :
now do something with those users
Add this user
Add this user
Add this user
Add this user
AS you can see, the problem is I want to call a function after I simply check if the users age is close to yours : +- 1 yr. How can I have it print "now do something..." after "add the user". Thank you so much!, Please respond if you have anything helpful at all, I am in need of anything.

Answer 1

You can use a DispatchGroup for this. You need to enter the dispatch group before you start each unit of asynchronous work and leave when that unit is complete. You can establish as closure to be executed when all work is complete using notify.
func getUsers() {
let ref = Database.database.reference()
if let myAget = self.myAgel {
ref.child("newUsers").observeSingleEvent(of: .value, with: {(snapshoter) in
if let valuer = snapshoter.value as? [String : AnyObject] {
let dispatchGroup = DispatchGroup()
for (one,_) in valuer {
dispatchGroup.enter()
checkCount.append("one")
ref.child("users").child(one).child("age").observeSingleEvent(of: .value, with: {(snap) in
if let agerti = snap.value as? Int {
if myAget - agerti <= 1 && myAget - agerti >= -1 {
print("Add this user")
}
}
dispatchGroup.leave()
})
}
dispatchGroup.notify {
print("now do something with those users")
}
}
})
}
}