https://felangel.github.io/bloc/#/flutterlogintutorial
我的代码在 GitHub 中: 链接 - https://github.com/mymomisacoder/bloc_login2
对于本教程,我想就如何在主页(登录时)添加/显示用户名寻求建议。
预期输入:
In login page, Login button is pressed after keying in username and password.
期望的事件:
Screen transit to the home page. Besides having a logout button in home page, username provided earlier is also shown.
我尝试了两种方法:
方法一:在userrepo类中创建一个getusername()
方法二:在userrepo类中赋值,通过blocprovider访问
class HomePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
final AuthenticationBloc authenticationBloc =
BlocProvider.of<AuthenticationBloc>(context);
final LoginBloc loginBloc = BlocProvider.of<LoginBloc>(context);
//method2
**//String username2 = loginBloc.usernamebloc;
//method1
String username2 = loginBloc.userRepository.getUserName().toString();**
print("$username2");
return Scaffold(
appBar: AppBar(
title: Text('Home'),
),
body: Container(
child: Center(
child: Column(
children: <Widget>[
RaisedButton(
child: Text('logout'),
onPressed: () {
authenticationBloc.dispatch(LoggedOut());
},
),
Center(
child: Text("Hello"),
**//child: Text("$username2"),**
),
],
),
),
),
);
}
}
用户 repo 类
class UserRepository {
String username1;
Future<String> authenticate({
@required String username,
@required String password,
}) async {
await Future.delayed(Duration(seconds: 1));
//method2
username1 = username;
return 'token';
}
Future<void> deleteToken() async {
/// delete from keystore/keychain
await Future.delayed(Duration(seconds: 1));
return;
}
Future<void> persistToken(String token) async {
/// write to keystore/keychain
await Future.delayed(Duration(seconds: 1));
return;
}
Future<bool> hasToken() async {
/// read from keystore/keychain
await Future.delayed(Duration(seconds: 1));
return false;
}
//method1
**Future<String> getUserName() async {
await Future.delayed(Duration(seconds: 1));
return username1;
}**
}
主页
class SimpleBlocDelegate extends BlocDelegate {
@override
void onEvent(Bloc bloc, Object event) {
super.onEvent(bloc, event);
print(event);
}
@override
void onTransition(Bloc bloc, Transition transition) {
super.onTransition(bloc, transition);
print(transition);
}
@override
void onError(Bloc bloc, Object error, StackTrace stacktrace) {
super.onError(bloc, error, stacktrace);
print(error);
}
}
void main() {
BlocSupervisor.delegate = SimpleBlocDelegate();
final userRepository = UserRepository();
runApp(
BlocProvider<AuthenticationBloc>(
builder: (context) {
return AuthenticationBloc(userRepository: userRepository)
..dispatch(AppStarted());
},
child: App(userRepository: userRepository),
),
);
}
class App extends StatelessWidget {
final UserRepository userRepository;
App({Key key, @required this.userRepository}) : super(key: key);
@override
Widget build(BuildContext context) {
return MaterialApp(
home: BlocBuilder<AuthenticationBloc, AuthenticationState>(
bloc: BlocProvider.of<AuthenticationBloc>(context),
builder: (BuildContext context, AuthenticationState state) {
if (state is AuthenticationUninitialized) {
return SplashPage();
}
if (state is AuthenticationAuthenticated) {
return HomePage();
}
if (state is AuthenticationUnauthenticated) {
return LoginPage(userRepository: userRepository);
}
if (state is AuthenticationLoading) {
return LoadingIndicator();
}
},
),
);
}
}
错误代码:
小部件库捕获的异常 以下断言被抛出构建主页(脏): 使用不包含 LoginBloc 类型的 Bloc 的上下文调用 BlocProvider.of()。 从传递给的上下文开始找不到祖先 BlocProvider.of()。 如果出现以下情况,就会发生这种情况: 1. 你使用的context来自BlocProvider上面的一个widget。 2. 您使用了 MultiBlocProvider 并且没有明确提供 BlocProvider 类型。
好:BlocProvider(构建器:(上下文)=> LoginBloc()) 错误:BlocProvider(构建器:(上下文)=> LoginBloc())。 使用的上下文是:HomePage(dirty)
最佳答案
我可以通过执行以下操作来解决问题。
更改了 UserRepository 中的 getUserName() 方法以返回 String(而不是 Future)。因此,代码如下所示:
String getUserName() {
return username1;
}
稍微修改了 HomePage 的定义以接受 UserRepository 参数。现在,定义如下所示:
class HomePage extends StatelessWidget {
final String userName;
HomePage({Key key, @required this.userName})
: super(key: key);
@override
Widget build(BuildContext context) {
// ...
最后,将 login bloc 行注释为恕我直言,它在您目前编写的整个主页代码中没有任何用处。新代码:
@override
Widget build(BuildContext context) {
final AuthenticationBloc authenticationBloc =
BlocProvider.of<AuthenticationBloc>(context);
//final LoginBloc loginBloc = BlocProvider.of<LoginBloc>(context);
//String username2 = loginBloc.usernamebloc;
String username2 = userName;
print("$username2");
这行得通。您将在控制台窗口中看到用户名。
关于Flutter Bloc 教程 - 如何显示用户名,即来自其他页面的值,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/57461821/