Flutter 用户成功登录后的AlertDialog或SnackBar

我需要一点帮助来解决一个我似乎不能完全理解的问题。我正在练习AWS，我需要在用户登录后为我的登录屏幕显示一条消息，或者在登录失败时显示一条错误消息。该消息假定位于AlertDialog或SnackBar中，但我不知道如何在一个按钮上调用两个函数，一个函数用于检查用户是否成功登录，另一个函数用于显示AlertDialog或SnackBar，其中包含函数

loginToCognito（）

中的错误消息或成功消息。简而言之，当用户按下登录按钮时，必须以AlertDialog或SnackBar的形式返回消息。以下是我迄今为止完成的代码：

import 'package:flutter/material.dart';
import 'package:flutter_client/modules/module2/components/login_form_buttons.dart';
import 'package:flutter_client/modules/module2/constants/styles.dart';
import 'package:amazon_cognito_identity_dart_2/cognito.dart';


class User {
  String email;
  String name;
  String password;
  bool confirmed = false;
  bool hasAccess = false;

  User({this.email, this.name});

  factory User.fromUserAttributes(List<CognitoUserAttribute> attributes) {
    final user = User();
    attributes.forEach((attribute) {
      if (attribute.getName() == 'email') {
        user.email = attribute.getValue();
      } else if (attribute.getName() == 'name') {
        user.name = attribute.getValue();
      }
    });
    return user;
  }
}

class UserService {
  CognitoUserPool _userPool;
  CognitoUser _cognitoUser;
  CognitoUserSession _session;
  UserService(this._userPool);
  CognitoCredentials credentials;

  Future<User> login(String email, String password) async {
    print('login initiated');
    _cognitoUser = CognitoUser(email, _userPool, storage: _userPool.storage);

    final authDetails = AuthenticationDetails(
      username: email,
      password: password,
    );

    bool isConfirmed;
    try {
      _session = await _cognitoUser.authenticateUser(authDetails);
      isConfirmed = true;
      print('logged in successfully');
    } on CognitoClientException catch (e) {
      if (e.code == 'UserNotConfirmedException') {
        isConfirmed = false;
      } else {
        rethrow;
      }
    }

    if (!_session.isValid()) {
      return null;
    }

    final attributes = await _cognitoUser.getUserAttributes();
    final user = User.fromUserAttributes(attributes);
    user.confirmed = isConfirmed;
    user.hasAccess = true;
    print(user);
    return user;
  }
}

class LoginScreen extends StatefulWidget {
  static const String id = 'login_screen';
  @override
  _LoginScreenState createState() => _LoginScreenState();
}

class _LoginScreenState extends State<LoginScreen> {
  bool showSpinner = false;
  String email;
  String password;
  final _userService = UserService(userPool);
  User _user = User();

  void loginToCognito() async {
    print('login button pressed, loggin with email, password: ' +
        email +
        ', ' +
        password);
    String message;
    try {
      _user = await _userService.login(email, password);
      message = 'User successfully logged in!';
      if (!_user.confirmed) {
        message = 'Please confirm user account';
      }
    } on CognitoClientException catch (e) {
      if (e.code == 'InvalidParameterException' ||
          e.code == 'NotAuthorizedException' ||
          e.code == 'UserNotFoundException' ||
          e.code == 'ResourceNotFoundException') {
        message = e.message;
      } else {
        message = 'An unknown client error occurred';
      }
    } catch (e) {
      message = 'An unknown error occurred';
      print('Unknown error while logging in:');
      print(e);
    }
    print(message);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.white,
      body: Padding(
        padding: EdgeInsets.symmetric(horizontal: 24.0),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            Flexible(
              child: Hero(
                tag: 'login',
                child: Container(
                  height: 200.0,
                  child: Image.asset('lib/modules/module2/images/login.png'),
                ),
              ),
            ),
            SizedBox(
              height: 48.0,
            ),
            TextField(
              keyboardType: TextInputType.emailAddress,
              textAlign: TextAlign.center,
              onChanged: (value) {
                //Do something with the user input.
                email = value;
              },
              decoration:
                  kTextFieldDecoration.copyWith(hintText: 'Enter your email'),
            ),
            SizedBox(
              height: 8.0,
            ),
            TextField(
              obscureText: true,
              textAlign: TextAlign.center,
              onChanged: (value) {
                //Do something with the user input.
                password = value;
              },
              decoration: kTextFieldDecoration.copyWith(
                  hintText: 'Enter your password'),
            ),
            SizedBox(
              height: 24.0,
            ),
            LoginFormButtons(
              buttonColour: Colors.grey,
              buttonText: 'Log In',
              buttonTextColour: Colors.white,
              onButtonPress: () {
                loginToCognito();
              },
            ),
          ],
        ),
      ),
    );
  }
}

---

提前感谢您的时间和帮助

简单地说，您希望向用户显示成功/失败消息。但你的目的的解决方案取决于你如何解释它

对我来说，我会像下面这样编码

try {
  // Unless we jump to catch scopes, everything is okay
  // So, returning the function in try scope will decrease complexity 
  _user = await _userService.login(email, password);
  message = 'User successfully logged in!';
  if (!_user.confirmed) {
    message = 'Please confirm user account';
  }
  // <====== Show your success dialog/toast etc. then return
  return;
} 

试试看{
//除非我们抓到望远镜，否则一切都好
//因此，在try范围内返回函数将降低复杂性
_user=wait\u userService.login（电子邮件、密码）；
消息='用户成功登录！'；
如果（！\u用户已确认）{
消息='请确认用户帐户'；
}
//非常好，非常感谢！
try {
  // Unless we jump to catch scopes, everything is okay
  // So, returning the function in try scope will decrease complexity 
  _user = await _userService.login(email, password);
  message = 'User successfully logged in!';
  if (!_user.confirmed) {
    message = 'Please confirm user account';
  }
  // <====== Show your success dialog/toast etc. then return
  return;
} 

on CognitoClientException catch (e) {
  if (e.code == 'InvalidParameterException' ||
      e.code == 'NotAuthorizedException' ||
      e.code == 'UserNotFoundException' ||
      e.code == 'ResourceNotFoundException') {
    message = e.message;
  } else {
    message = 'An unknown client error occurred';
  }
} catch (e) {
  message = 'An unknown error occurred';
  print('Unknown error while logging in:');
  print(e);
}
// <====== Show your fail dialog/toast etc.