Question

我需要在另一个提供者内部使用一个提供者，但我无法做到这一点，我试图使用ChangeNotifierProxyProvider，但未调用更新功能。

我有2个提供程序，UserProvider和RoleProvider，我需要在UserProvider内部调用RoleProvider或在用登录用户更新UserProvider之后调用RoleProvider。

providers: [
  ChangeNotifierProvider(create: (ctx) => UserProvider(),),
  ChangeNotifierProxyProvider<UserProvider, RoleProvider>(
    create: (_) => RoleProvider(null),
    update: (_, userProvider, roleProvider) => RoleProvider(userProvider),
  ),
],

class UserProvider with ChangeNotifier {
  User user;

  Future<void> login(String username, String password) async {  
    this.loginMessage = '';
    try {
      // Login Process
      this.user = new User();
      // When there is a new logged user, I need to doSomething in RoleProvider
    } catch (e) {
      print(e);
      this.loginMessage = 'ERROR';
    }
    notifyListeners();
  }
}

class RoleProvider with ChangeNotifier {
  final UserProvider userProvider;
  List<Student> students;

  RoleProvider(this.userProvider) {
    print('PARENT PROVIDER CONSTRUCTOR');
  }

  fetchData() {
    print('TEEEEEEEEST');
  }

}

Answer 1

providers: [
  ChangeNotifierProvider(create: (ctx) => UserProvider(),),
  ChangeNotifierProxyProvider<UserProvider, RoleProvider>(
    create: (_) => RoleProvider(),
    update: (_, userProvider, roleProvider) => roleprovider.userProvider = userProvider,
    // use the roleProvider reference instead of creating a new RoleProvider in the update
  ),
],

class RoleProvider with ChangeNotifier {
  UserProvider userProvider; // No final, if you want to consume one provider inside another
                             // then just leave it so you can then update its value
  List<Student> students;

  // No need to use the constructor if you're not going to do anything else besides declare userProvider

  fetchData() {
    print('TEEEEEEEEST');
  }

}

如何在另一个提供者内部消费提供者

1 个答案: