Swift - Using a closure inside a repeat loop

Question

I am trying to implement a user registration system and I need to know whether a user id (generated randomly) has already been assigned to another user or not. To do so, I connect my Firebase database and use the observer() method to check to availability of the generated id.

However, since the Firebase database query runs asynchronously and I can only know the result once the query returns, I am not able to use the correct return value from within the calling method.

My approach here is

repeat {
  id = generateUniqueId()
  check availability
} while (id is not unique)

The implementation I have is

var id:String
var test = true
repeat {
    id = generateId()
    ref.child("\(databaseReferenceName)").observe(.value) { (snapshot) in
        test = snapshot.hasChild("\(id)")
    }
} while (test == true)

This loop keeps running even though the test variable is set to false by the hasChild() method.

How can I change the code so that I would be able to capture the right value of the test variable?

I am using Swift 4.1

Thanks

Answer 1

Since the process is asynchronous the loop will run until hit the first test = false , but i think you need this recursive way until find an available id

func checkID() {

       id = generateId()
       ref.child("\(databaseReferenceName)").observeSingleEvent(.value) { (snapshot) in
         let test = snapshot.hasChild("\(id)")

         if test {
           print("id exists")
           checkID() // check another one
         }
         else {
          print("this is the one \(id)")
         }
       }

}

another thing is that it should be observeSingleEvent instead of observe