swift - ''Value of type ' AuthDataResult ?' has no member ' uid '''

Question

@IBAction func SignUpBtn_TouchUpInside(_ sender: Any) {

Auth.auth().createUser(withEmail: emailTextField.text!, password: passwordTextField.text!, completion:  { (user: AuthDataResult?, error:Error?) in
    if error != nil{
        print(error?.localizedDescription)
        return

}

let ref = Database.database().reference()
let usersRenfence = ref.child("users")

let uid = user.uid 
//(HERE IS WRONG, I DONT KNOW WHAT SHOULD I DO. It's my first time study code.)
let newUserRefernce = ref.child(uid)
newUserRefernce.setValue{["username": self.usernameTextField.text!, "email": self.emailTextField.text!]

print("description: \(newUserRefernce.description())")

Answer 1

替换

let uid = user.uid 

与

let uid = user!.user.uid 

看这里Docs