未处理的异常：NoSuchMethodError：方法“findAncestorStateOfType”在 null 上被调用

Question

由于以下错误，我的应用卡在 HandleMainScreen。它第一次正确导航，但在控制台中出现错误，但是当我热重启时，导航不起作用，应用程序卡在 HandleMainScreen。

E/flutter ( 8785): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: NoSuchMethodError: The method 'findAncestorStateOfType' was called on null.
E/flutter ( 8785): Receiver: null
E/flutter ( 8785): Tried calling: findAncestorStateOfType<NavigatorState>()
E/flutter ( 8785): #0      Object.noSuchMethod  (dart:core-patch/object_patch.dart:53:5)
E/flutter ( 8785): #1      Navigator.of 
package:flutter/…/widgets/navigator.dart:2115
E/flutter ( 8785): #2      _HandleMainScreenState.checkAuthentication.<anonymous closure> 
package:monktree/main.dart:58
E/flutter ( 8785): #3      _rootRunUnary  (dart:async/zone.dart:1192:38)
E/flutter ( 8785): #4      _CustomZone.runUnary  (dart:async/zone.dart:1085:19)
E/flutter ( 8785): #5      _CustomZone.runUnaryGuarded  (dart:async/zone.dart:987:7)
E/flutter ( 8785): #6      _BufferingStreamSubscription._sendData  (dart:async/stream_impl.dart:339:11)
E/flutter ( 8785): #7      _BufferingStreamSubscription._add  (dart:async/stream_impl.dart:266:7)

以下代码是我正在使用的。如果您有任何更好的方式来处理用户，请在这个问题上回答它。

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      builder: (context, child) {
        return ScrollConfiguration(
          behavior: MyBehavior(),
          child: child,
        );
      },
      home: HandleMainScreen(),
      debugShowCheckedModeBanner: false,
    );
  }
}
class MyBehavior extends ScrollBehavior {
  @override
  Widget buildViewportChrome(
      BuildContext context, Widget child, AxisDirection axisDirection) {
    return child;
  }
}
class HandleMainScreen extends StatefulWidget {
  @override
  _HandleMainScreenState createState() => _HandleMainScreenState();
}

class _HandleMainScreenState extends State<HandleMainScreen> {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  bool isLoggedIn;
  FirebaseUser _user;
  String error;

  @override
  void initState() {
    super.initState();
    checkAuthentication();
  }

  checkAuthentication() async {
    _auth.onAuthStateChanged.listen((user) {
      _user = user;
      if (user == null) {
        Navigator.of(context).pushReplacement(
            MaterialPageRoute(builder: (context) => LoginPage()));
      } else if (user != null) {
        Navigator.of(context).pushReplacement(
            MaterialPageRoute(builder: (context) => HomePage(user)));
      }
    }).onError((e) {
      error = e.toString();
      print("Error in HandleMainScreen\n" + e.toString());
    });
  }

  @override
  Widget build(BuildContext context) {
    Constants.allocateSize(size: MediaQuery.of(context).size);
    return Scaffold(
      body: Center(
        child: CircularProgressIndicator(),
      ),
    );
  }
}

Answer 1

改变这个：

  checkAuthentication() async {
    _auth.onAuthStateChanged.listen((user) {
      _user = user;
      if (user == null) {
        Navigator.of(context).pushReplacement(
            MaterialPageRoute(builder: (context) => LoginPage()));
      } else if (user != null) {
        Navigator.of(context).pushReplacement(
            MaterialPageRoute(builder: (context) => HomePage(user)));
      }
    }).onError((e) {
      error = e.toString();
      print("Error in HandleMainScreen\n" + e.toString());
    });
  }

进入这个：

  checkAuthentication() async {
    _auth.onAuthStateChanged.listen((user) {
      _user = user;
      if (user == null) {
        Navigator.pushReplacement(
          context,
          MaterialPageRoute(builder: (context) => LoginPage()),
        );
      } else if (user != null) {
         Navigator.pushReplacement(
          context,
          MaterialPageRoute(builder: (context) => HomePage(user)),
        );
      }
    }).onError((e) {
      error = e.toString();
      print("Error in HandleMainScreen\n" + e.toString());
    });
  }