在null上调用getter“uid”。接收者：null尝试调用：uid

Question

此错误“”getter'uid'在null上被调用。receiver：null尝试调用：uid“

class Wrapper extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final user = Provider.of<User_fb>(context);

    // return home or login
    if (user == null) {
      return Login();
    } else {
      print(user.uid);

      return Home();
    }
  }
}

Future Signinwithemailandpassword(var Res_email,var Res_Password) async{

    try{
        UserCredential result= await _auth.signInWithEmailAndPassword(email: Res_email, password: Res_Password);
        User user = result.user;
        return _userfromfirebase(user);
    }catch(e){
      return null;
    }

}

Future signOut () async{
try{
  return await _auth.signOut();
}
catch(e){
print(e.toString());
print("error at signOut ");
return null;
}
}

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  await Firebase.initializeApp();

  runApp(Main());
}

class Main extends StatefulWidget {
  @override
  _MainState createState() => _MainState();
}

class _MainState extends State<Main> {
  @override
  Widget build(BuildContext context) {

    return StreamProvider<User_fb>.value(
      value: Authservice().user,
      child: MaterialApp(
        debugShowCheckedModeBanner: false,
        theme: ThemeData(
            primaryColor: Color.fromRGBO(255, 255, 255, 1),
            shadowColor: Colors.transparent,
            highlightColor: Colors.transparent),
        home: Wrapper(),

      ),
    );
  }
}

退出按钮：

ListTile(
                       leading: Icon(Ionicons.log_out_outline,
                           color: Color.fromRGBO(86, 197, 150, 1)),
                       title: Text('Log out'),
                       onTap: () async {
                         await _auth.signOut();
                       },
                     ),

html" target="_blank">控制台：

widgets库捕获的异常接收者：null尝试调用：uid

相关的导致错误的小部件是：Qr file://g://androidstudioprojects/facem/lib/screens/home/home.dart:687:67当抛出异常时，这是堆栈:#0 object.nosuchmethod(dart:core-patch/object_patch.dart:54:5)#1_qrstate.build（包:my_compound/screens/Qr/Qr.dart:99:45)#2 statefulelement.build（包Fulelement.performRebuild（包:flutter/src/widgets/framework.dart:4746:11)...

Answer 1

发生这种情况是因为user为null，所以使用null检查运算符。像这样的用户？。uid或user.uid？？''，

提示：在使用颤振时，始终使用省道零安全。