SignupPressed.swift

    @IBAction func signUpPressed(_ sender: UIButton) {
        // Validate the field, 先對textField做判斷
        let error = validateTextField()
        if error != nil {
            popAlert(title: "Error occured", message: error!, alertTitle: "OK") { (action) in
                self.emailTextField.text = ""
                self.passwordTextField.text = ""
                self.repasswordTextField.text = ""
                self.userNameTextField.text = ""
            }
        } else {
            // 將textField輸入的文字存入常數中
            if let email = emailTextField.text,
               let password = passwordTextField.text,
               let userName = userNameTextField.text {
                // 建立user
                Auth.auth().createUser(withEmail: email, password: password) { authResult, error in
                    if let error = error {
                        self.popAlert(title: "Error occured", message: error.localizedDescription, alertTitle: "OK") { (action) in
                            self.emailTextField.text = ""
                            self.passwordTextField.text = ""
                            self.repasswordTextField.text = ""
                            self.userNameTextField.text = ""
                        }
                    } else {
                        self.db.collection(Constant.FireStore.users).addDocument(data: [Constant.FireStore.userName: userName, Constant.FireStore.uid: authResult!.user.uid]) { (error) in
                            if let error = error {
                                print(error)
                            } else {
                                if let currentUser = Auth.auth().currentUser?.createProfileChangeRequest() {
                                    currentUser.displayName = userName
                                    currentUser.commitChanges { (error) in
                                        if let error = error {
                                            print(error)
                                        } else {
                                            if let user = Auth.auth().currentUser {
                                                self.uid = user.uid
                                                self.performSegue(withIdentifier: Constant.Segue.signupSegue, sender: self)
                                                print("sign up success!")
                                                print(currentUser.displayName!)
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }