Retrieving value from database - swift3

Question

Hi I have a problem and would be grateful to any advice or answer.
func getUserProfileMDP(){
// set attributes to textField
var ref: DatabaseReference!
ref = Database.database().reference()
let user = Auth.auth().currentUser
print(user!.uid)
ref.child("users").child((user?.uid)!).observeSingleEvent(of: .value, with: { (snapshot) in
// Get user value
guard let value = snapshot.value as? [String: String] else { return }
print(value)
let passwordValue = value["password"]!as! String
print(passwordValue)
self.MDP = passwordValue // prints the right value from database
}){ (error) in
print(error.localizedDescription)
}
print(self.MDP) // prints the value innitialised in class(nope)
}
Here is the function that gets the value from database. It works (the first print gets the right value)
#IBAction func register(_ sender: Any) {
print(self.MDP)// prints the value innitialised in class(nope)
getUserProfileMDP()
print(self.MDP) // prints the value innitialised in class(nope)
let MDP = self.MDP
That is were I need the password to compare it. It doesn't get me the value of the database but the value initialized in class above:
var MDP = "nope"
Have a nice day

Answer 1

Given your last comment, I'd say that you're almost there, but here's an example. I did not fix the other parts of your code, I only added the completion handler in the method signature, and passed the password value to the handler, to show you how this works. The handler must be called inside the async closure.
func getUserProfileMDP(completion: #escaping (String)->()) {
// set attributes to textField
var ref: DatabaseReference!
ref = Database.database().reference()
let user = Auth.auth().currentUser
print(user!.uid)
ref.child("users").child((user?.uid)!).observeSingleEvent(of: .value, with: { (snapshot) in
// Get user value
guard let value = snapshot.value as? [String: String] else { return }
print(value)
let passwordValue = value["password"]!as! String
completion(passwordValue)
}){ (error) in
print(error.localizedDescription)
}
}
And you call it like that:
getUserProfileMDP() { pass in
print(pass)
self.MDP = pass
}