Flutter中利用SharedPreferences实现用户登录状态持久化的方法求助

Hey there! Let's get that login persistence sorted out for you. The core issue here is that while you're saving user data to SharedPreferences after a successful login, your app isn't checking that saved data when it starts up. Here's how to fix this step by step:

1. Check Login Status on App Startup #

First, we need to verify if there's a saved user session when the app launches. Modify your main.dart to check SharedPreferences before deciding which screen to show:

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'login.dart';
import 'my_widget.dart';

void main() async {
  // Required to use SharedPreferences before runApp()
  WidgetsFlutterBinding.ensureInitialized();
  
  SharedPreferences prefs = await SharedPreferences.getInstance();
  // Check if we have a saved user object
  String savedUser = prefs.getString('user');

  runApp(MaterialApp(
    title: 'Your App',
    // Navigate to home if user exists, else login screen
    home: savedUser != null ? MyWidget() : Login(),
    debugShowCheckedModeBanner: false,
  ));
}

2. Improve Login Success Navigation #

Right now, you're using Navigator.push() which keeps the login screen in the navigation stack. Use pushReplacement() instead so users can't navigate back to the login screen after logging in:

Update the login success logic in your loginUser() method:

authentication.login(email, password).then((user) {
  if (user != null) {
    Navigator.pushReplacement( // Use pushReplacement here
      context,
      MaterialPageRoute(builder: (context) => MyWidget())
    );
  }
}).catchError((error) {
  ScaffoldMessenger.of(context)
    .showSnackBar(SnackBar(content: Text(error.toString())));
});

3. Add a Logout Functionality #

To let users properly end their session, add a logout method that clears saved data from SharedPreferences and navigates back to the login screen. For example, in your MyWidget:

void logout() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  // Clear all saved session data (or remove specific keys if needed)
  await prefs.remove('user');
  await prefs.remove('access_token');
  await prefs.remove('id');
  
  Navigator.pushReplacement(
    context,
    MaterialPageRoute(builder: (context) => Login())
  );
}

You can call this method from a button in MyWidget:

ElevatedButton(
  onPressed: logout,
  child: Text('Se déconnecter'),
)

4. Verify SharedPreferences Saving #

Double-check that your login function is correctly saving the user data. Add a quick print statement to confirm the data is being stored:

In your login API function:

if (body['code'] == 0) {
  SharedPreferences localStorage = await SharedPreferences.getInstance();
  localStorage.setInt('id', body['user']['id']);
  localStorage.setString('adress', body['user']['adress']);
  localStorage.setString('phone', body['user']['phone']);
  localStorage.setString('access_token', body['access_token']);
  localStorage.setString('user', json.encode(body['user']));
  
  // Verify the save
  String savedUser = localStorage.getString('user');
  print('Saved User Data: $savedUser'); // Check console for this output
  return user;
}

Key Notes #

• Make sure your User.fromJson method correctly parses the saved JSON string if you need to reconstruct the User object later.
• Always use WidgetsFlutterBinding.ensureInitialized() when accessing SharedPreferences before runApp().
• For added security, consider encrypting sensitive data like access tokens before storing them in SharedPreferences.

Give these changes a go, and your users should stay logged in across app restarts until they choose to log out. Let me know if you hit any snags along the way!

内容的提问来源于stack exchange，提问作者lucky