flutter - Flutter - NoSuchMethodError：在 null 上调用了 getter 'focusScopeNode'

Question

尝试List从一个屏幕传递到另一个屏幕时出现以下错误。数据正在从async函数传递。我需要根据从数据库中获取的数据打开另一个屏幕。这里提到的答案对我不起作用。这是错误。

: [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: NoSuchMethodError: The 
getter 'focusScopeNode' was called on null.
E/flutter (26425): Receiver: null    
E/flutter (26425): Tried calling: focusScopeNode
E/flutter (26425): #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
E/flutter (26425): #1      Route.didPush.<anonymous closure> (package:flutter/src/widgets/navigator.dart:139:17)    

异步函数中的代码

 Navigator.push(context, MaterialPageRoute(builder: (context) {
    return ParentHome(childList);

家长主屏幕

      class ParentHome extends StatefulWidget {
  List childDataList;

  ParentHome(this.childDataList);

  @override
  State<StatefulWidget> createState() {
    return ParentHomeWidget();
    }
   }
class ParentHomeWidget extends State<ParentHome> {
  @override
  Widget build(BuildContext context) {
// TODO: implement build
return MaterialApp(
  home: Scaffold(
    body: Container(
      margin: EdgeInsets.all(5),
      child: ListView.builder(
          itemCount: widget.childDataList.length,
          itemBuilder: (BuildContext context, int index) => ListTile(
                title: Text(widget.childDataList[index]['title']),
              )),
    ),
      ),
    );
  }
}

我没有找到任何帮助。请帮我解决这个问题。我还是 Flutter 的新手。谢谢

颤振医生输出

Flutter（Channel stable，v1.12.13+hotfix.5，在 Linux 上，语言环境 en_US.UTF-8）
• Flutter 版本 1.12.13+hotfix.5，位于 /home/jamshaid/Documents/flutter_linux_v1.9.1+hotfix.4-stable /flutter
• 框架修订 27321ebbad（6 周前），2019-12-10 18:15:01 -0800 • 引擎修订 2994f7e1e6
• Dart 版本 2.7.0
完成同步功能

Future<void> requestLogin(String userType) async {
/*
final response =
    await http.get('http://10.0.2.2/php_to_flutter/login_validation.php');*/
String databaseAddress = "";

switch (userType) {
  case "Student":
    databaseAddress = AppUtils.studentLoginLink;
    break;
  case "Parent":
    databaseAddress = AppUtils.parentLoginLink;

    break;
  case "Teacher":
    databaseAddress = AppUtils.teacherLoginLink;
    break;
}

    final response = await http
    .post(databaseAddress, body: {"email": email, "password": password});
String responseBody = response.body;

if (response.statusCode == 200) {
  switch (userType) {
    case "Student":
      print("Registration # $responseBody");
      break;
    case "Parent":
      List childList = responseBody.split(",");
      //child list needs to be separated by :
      /*Navigator.of(context).push(
          MaterialPageRoute(builder: (context) => ParentHome(childList)));
      */
      Navigator.push(context, MaterialPageRoute(builder: (context) {
        return ParentHome(childList);
      }));
      //Navigator.pop(context);

      print("Child List= $responseBody");
      break;
    case "Teacher":
      print("Teacher id= $responseBody");
      break;
  }
  form_key.currentState.reset();
  //dismissing progress dialog
  Navigator.pop(context);
  Toast.show("Login Successful", context,
      duration: Toast.LENGTH_SHORT, gravity: Toast.CENTER);
 } else {
   Navigator.pop(context);
  print(databaseAddress);

  Toast.show("Error: " + response.statusCode.toString(), context,
      duration: Toast.LENGTH_SHORT, gravity: Toast.CENTER);

  print('error' + response.body);
  print(response.statusCode);
 }
 }

异步调用者代码 异步函数正在被onPressed调用RaisedButton。

Widget studentLoginButton() {
    return RaisedButton(
      onPressed: () {
        if (form_key.currentState.validate()) {
          form_key.currentState.save();
          //  pr.show();
          AppUtils.showProgressDialog(context, "Loggin in...");
          requestLogin("Student");
          form_key.currentState.reset();

          //pr.dismiss();
        }

        // form_key.currentState.reset();
      },
      child: Text('S Login'),
      color: Colors.lightBlue,
    );
  }

标签： flutterstatefulwidget

Answer 1

Navigator.pop(context);在 switch 块之后还有另一个。default如果没有任何案例匹配，则如果打算返回导航，请尝试删除该案例或设置案例。

switch (userType) {
    case "Student":
      print("Registration # $responseBody");
      break;
    case "Parent":
      List childList = responseBody.split(",");
      //child list needs to be separated by :
      /*Navigator.of(context).push(
          MaterialPageRoute(builder: (context) => ParentHome(childList)));
      */
      Navigator.push(context, MaterialPageRoute(builder: (context) {
        return ParentHome(childList);
      }));
      //Navigator.pop(context);

      print("Child List= $responseBody");
      break;
    case "Teacher":
      print("Teacher id= $responseBody");
      break;
  }
  form_key.currentState.reset();
  //dismissing progress dialog
  //Navigator.pop(context);
  Toast.show("Login Successful", context,
      duration: Toast.LENGTH_SHORT, gravity: Toast.CENTER);

或者

switch (userType) {
    case "Student":
      print("Registration # $responseBody");
      break;
    case "Parent":
      List childList = responseBody.split(",");
      //child list needs to be separated by :
      /*Navigator.of(context).push(
          MaterialPageRoute(builder: (context) => ParentHome(childList)));
      */
      Navigator.push(context, MaterialPageRoute(builder: (context) {
        return ParentHome(childList);
      }));
      //Navigator.pop(context);

      print("Child List= $responseBody");
      break;
    case "Teacher":
      print("Teacher id= $responseBody");
      break;
    default:
      form_key.currentState.reset();
      //dismissing progress dialog
      Navigator.pop(context);
      Toast.show("Login Successful", context,
        duration: Toast.LENGTH_SHORT, gravity: Toast.CENTER);
  }