Function will not call Swift 3 - swift

Question

#IBAction func signup(_ sender: Any) {
print("began signup process")
guard let fullname = fullnameField.text, fullname != "" else {
print("FULLNAME field is empty")
return
}
guard let username = usernameField.text, username != "" else {
print("USERNAME field is empty")
return
}
guard let email = emailField.text, email != "" else {
print("EMAIL field is empty")
return
}
guard let password = passwordField.text, password != "" else {
print("PASSWORD field is empty")
return
}
print("all fields good")
mainActivityIndicator.startAnimating()
self.checkUsernameAvailability(username: username, completion: {
result in
print("starting check")
...
})
print("finished the function")
}
The issue is basically that nothing inside of the checkUsernameAvailability function will call.
The console looks like this:
began signup process
all fields good
finished the function
it does not print 'starting check' or run any code at all inside of the function.
This is probably a rookie error and I am sorry if it is a stupid question.
Future thanks.
P.S I checked the entire console and there is no error relating to this.
EDIT: Here is the code inside the function
func checkUsernameAvailability(username: String, completion: #escaping (Bool) -> Void) {
_ = Database.database().reference().child("usernames").observe(.childAdded, with: {
snapshot in
print("checking username availability")
print(snapshot)
completion(true)
let dict = snapshot.value as? [String: AnyObject]
for handled in (dict?.values)! {
print("stumbled")
print(handled)
if username.lowercased() == handled.lowercased {
completion(false)
}
}
})
}
And...
self.checkUsernameAvailability(username: username, completion: {
result in
print("starting check")
if result == false {
print("username is taken")
self.mainActivityIndicator.stopAnimating()
return
} else {
Auth.auth().createUser(withEmail: email, password: password, completion: {
(user, error) in
if error != nil {
print(error ?? "ERROR OCCURED")
self.mainActivityIndicator.stopAnimating()
return
}
let ref = Database.database().reference()
ref.child("~/users/\(user?.uid ?? "0")/username").setValue(username.lowercased())
ref.child("~/users/\(user?.uid ?? "0")/fullname").setValue(fullname)
ref.child("usernames/\(user?.uid ?? "0")").setValue(username.lowercased())
self.mainActivityIndicator.stopAnimating()
})
}
})

Answer 1

The Database.database().reference().child("usernames").observe call simply never calls the with block. I would assume that block is called when the event .childAdded is observed, but I see no code that would add a child. To me this looks like you are setting up an asynchronous observer, so this code will not run when you make the call, it will run when the monitored event takes place.