I am creating a project where I want to create a list of students and store it and then edit or delete whenever required. I am locally storing data and using sqlite. But while running the project I receive following error: Class 'Future' has no instance getter 'key'. Receiver: Instance of 'Future' Tried calling: key Getting error in if (studentList==null) E/flutter (11424): [ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: LateInitializationError: Field 'studentList' has not been initialized.

class StudentList extends StatefulWidget {
  final String? streenTitle;

  StudentList(this.streenTitle);
  State<StatefulWidget> createState() {
    return StudentState();
  }
}

class StudentState extends State<StudentList> {
  SQL_Helper? helper = SQL_Helper();
  late List<Student> studentList;
  int connt = 0;

  build(BuildContext context) async {
    **if (studentList==null) {**
      studentList = await <Student>[];
    }

    return Scaffold(
      appBar: AppBar(
        title: Text("Students"),
      ),
      body: getStudentsList(),
      floatingActionButton: FloatingActionButton(onPressed: () {
        NavigatorToStudend("Add New Studend");
      }),
    );
  }

  ListView getStudentsList() {
    return ListView.builder(
        itemCount: connt,
        itemBuilder: (BuildContext context, int pos) {
          return Card(
            color: Colors.red,
            elevation: 2.0,
            child: ListTile(
              leading: CircleAvatar(
                backgroundColor: isPassed(this.studentList[pos].pass),
                child: getIcon(this.studentList[pos].pass),
              ),
              title: Text(this.studentList[pos].name),
              subtitle: Text(this.studentList[pos].description  
                  " | "  
                  this.studentList[pos].date),
              trailing: GestureDetector(
                child: Icon(Icons.delete, color: Colors.green),
                onTap: () {
                  _delete(context, this.studentList[pos]);
                },
              ),
              onTap: () {
                NavigatorToStudend("Edit Sdudent");
              },
            ),
          );
        });
  }

  Color isPassed(int value) {
    switch (value) {
      case 1:
        return Colors.amber;
        break;
      case 2:
        return Color.fromARGB(255, 10, 95, 63);
        break;
    }
    return isPassed(value);
    //// stop in 15:28
  }

  Icon getIcon(int value) {
    switch (value) {
      case 1:
        return Icon(Icons.check);
        break;
      case 2:
        return Icon(Icons.close);
        break;
    }
    return getIcon(value);
  }

  void NavigatorToStudend(String appTitle) {
    Navigator.push(context, MaterialPageRoute(builder: (context) {
      return StudentDetil(appTitle);
    }));
  }
}

void _delete(BuildContext context, Student student) async {
  

  int result = await SQL_Helper.helper!.deleteStudent(student.id);
  if (result != 0) {
    _showSenchBar(context, " Student is been deleted");

    //listview
  }
}

void _showSenchBar(BuildContext context, String mag) async {
  final snackBar = await SnackBar(content: Text(mag));
  Scaffold.of(context).showSnackBar(snackBar);
}

//void NavigatorToStudend(String s) {}

CodePudding user response：

There's a few issues with your code. For starters: late List<Student> studentList; isn't nullable, so checking if (studentList==null) { will always be false. There's a few typos and code errors too (such as your build method not having an @override decorator. I highly suggest using an IDE (like Android Studio) if you aren't already.

If studentList is always going to be awaiting something, I suggest using a FutureBuilder