我的第一个屏幕是登录屏幕，它需要检查用户是否已登录才能直接打开主屏幕，但是使用此检查却出现错误。
我正在检查initState，条件返回的是true，所以看起来问题出在导航器上。
如果用户已登录，跳过第一个屏幕的正确方法是什么？
错误：
I/flutter (20803): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (20803): The following assertion was thrown building Navigator-[GlobalObjectKey<NavigatorState>
I/flutter (20803): _WidgetsAppState#8ce27](dirty, state: NavigatorState#db484(tickers: tracking 2 tickers)):
I/flutter (20803): 'package:flutter/src/widgets/navigator.dart': Failed assertion: line 2106 pos 12: '!_debugLocked':
I/flutter (20803): is not true.
I/flutter (20803): Either the assertion indicates an error in the framework itself, or we should provide substantially
I/flutter (20803): more information in this error message to help you determine and fix the underlying cause.
码：
class LoginScreen extends StatefulWidget {
@override
_LoginScreenState createState() => _LoginScreenState();
}
class _LoginScreenState extends State<LoginScreen> {
final _emailController = TextEditingController();
final _passController = TextEditingController();
final _formKey = GlobalKey<FormState>();
final _scaffoldKey = GlobalKey<ScaffoldState>();
@override
void initState() {
super.initState();
if(FirebaseAuth.instance.currentUser() != null){
Navigator.of(context).pushReplacement(MaterialPageRoute(
builder: (context) => HomeScreen()
));
}
}
@override
Widget build(BuildContext context) {
return Scaffold(
key: _scaffoldKey,
body: ScopedModelDescendant<UserModel>(
builder: (context, child, model){
if(model.isLoading)
return Center(
child: CircularProgressIndicator(),
);
return Form(
key: _formKey,
child: ListView(
padding: EdgeInsets.all(16),
children: <Widget>[
SizedBox(height: 67),
Icon(Icons.chrome_reader_mode, size: 150, color: Colors.blue,),
SizedBox(height: 16,),
TextFormField(
controller: _emailController,
decoration: InputDecoration(
hintText: "Digite seu e-mail",
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10),
),
fillColor: Colors.blueAccent
),
keyboardType: TextInputType.emailAddress,
validator: (text){
if(text.isEmpty || !text.contains("@"))
return "E-mail inválido!";
},
),
SizedBox(height: 16,),
TextFormField(
controller: _passController,
decoration: InputDecoration(
hintText: "Digite sua senha",
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(10),
),
fillColor: Colors.blueAccent
),
obscureText: true,
validator: (text){
if(text.isEmpty || text.length < 6)
return "Digite a senha!";
},
),
SizedBox(height: 16,),
FlatButton(
padding: EdgeInsets.all(13),
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(10)
),
color: Colors.blue,
child: Text("Entrar",
style: TextStyle(
color: Colors.white,
fontSize: 20
),
),
onPressed: (){
if(_formKey.currentState.validate()){
model.signIn(
email: _emailController.text,
pass: _passController.text,
onSuccess: _onSuccess,
onFail: _onFail,
);
}
},
),
SizedBox(height: 10,),
InkWell(
onTap: (){
if(_emailController.text.isEmpty || !_emailController.text.contains("@")){
_scaffoldKey.currentState.showSnackBar(
SnackBar(content: Text("Insira um e-mail válido para recuperação",
style: TextStyle(fontSize: 14),
),
backgroundColor: Colors.redAccent,
duration: Duration(seconds: 3),
)
);
} else {
model.recoverPass(_emailController.text);
_scaffoldKey.currentState.showSnackBar(
SnackBar(
content: Text("O e-mail de recuperação foi enviado!",
style: TextStyle(fontSize: 14),
),
backgroundColor: Colors.green,
duration: Duration(seconds: 3),
)
);
}
},
child: Text("Esqueci minha senha",
style: TextStyle(
color: Colors.black,
fontSize: 16,
fontWeight: FontWeight.w400
),
textAlign: TextAlign.center,
),
),
SizedBox(height: 30,),
InkWell(
onTap: (){
Navigator.of(context).push(MaterialPageRoute(
builder: (context)=> SignUpScreen())
);
},
child: Text("Não tem conta? Cadastre-se!",
style: TextStyle(
color: Colors.black,
fontSize: 16,
fontWeight: FontWeight.w600
),
textAlign: TextAlign.center,
),
),
],
),
);
},
),
);
}
}
好吧，您可以使用另一种方法来解决此类问题。而是检查您的loginScreen类中是否有用户登录，您可以在此之前执行此步骤，然后决定是否有用户登录时是否显示loginScreen或显示另一个屏幕（我假设是MainScreen）（如果用户已经登录） 。
我将简要介绍如何完成此操作。希望对您有所帮助。但是在我向您解释源代码中有什么问题之前，请先进行说明。
if(FirebaseAuth.instance.currentUser() != null){
// wrong call in wrong place!
Navigator.of(context).pushReplacement(MaterialPageRoute(
builder: (context) => HomeScreen()
));
}
您的代码已损坏，因为它currentUser()是一个异步函数，并且在您进行调用时，此函数将返回一个不完整的Future对象，该对象是一个非null的对象。因此，导航pushReplacement器始终被调用，并且由于小部件的状态尚未就绪而崩溃。
作为解决方案，您可以使用FutureBuilder并确定将打开哪个屏幕。
int main(){
runApp( YourApp() )
}
class YourApp extends StatelessWidget{
@override
Widget build(BuildContext context){
return FutureBuilder<FirebaseUser>(
future: FirebaseAuth.instance.currentUser(),
builder: (BuildContext context, AsyncSnapshot<FirebaseUser> snapshot){
if (snapshot.hasData){
FirebaseUser user = snapshot.data; // this is your user instance
/// is because there is user already logged
return MainScreen();
}
/// other way there is no user logged.
return LoginScreen();
}
);
}
}
使用这种方法，您可以避免LoginScreen类来验证是否有用户登录！
建议您可以将snapshot.connectionState属性与一起使用，switch case以实现更精细的控件。
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