如何更新用户资料

Question

当我的用户登录到用户配置文件时，用户名是默认用户名，它将保留为“ username”而不是该用户的自定义用户名 从firebase数据库注册。您如何解决此代码以从Firebase数据库上载用户名？

let displayName = displayNameText.text
        DatabaseRef = Database.database().reference()
            let changeRequest = Auth.auth().currentUser?.createProfileChangeRequest()
            changeRequest?.displayName = displayName
            changeRequest?.commitChanges { (error) in
              // ...
            }
            if let userID = Auth.auth().currentUser?.uid{
                DatabaseRef.child("users").child(userID).observeSingleEvent(of: .value, with: { (snapshot) in
                    let dictionary = snapshot.value as? NSDictionary
                    let username = dictionary?["username"] as? String ?? "username"
                    self.displayNameText.text = username