Android studio flatter SQFlite：在使用数据库内容更新listview时遇到问题

我确实设法通过listview显示了数据库内容。然而，它没有做得很好。只要我运行模拟器，数据库中存储的内容就会出现，但不会出现。它还显示数据库是空的，尽管它显然不是空的。但是，一旦我向数据库中添加了一个新项目并单击“保存”，所有内容都会显示出来（除了上次添加的项目，它会在下次更新时显示）。我不知道如何解决这个问题，我尝试将_listtoos（）放在任何地方，看看它是否在小部件之前执行，但没有任何改进我想问题出在ListDisplay类中，因此您可以跳过其余部分，为了方便起见，我只需要完整的代码

import 'package:flutter/material.dart';

import 'model/todo_model.dart';
import 'model/todo.dart';

class ListGradesPage extends StatefulWidget {
  final String title;

  ListGradesPage({this.title, Key key}) : super(key: key);

  _ListGradesPageState createState() => _ListGradesPageState();
}

var _todoItem;
var _lastInsertedId = 0;
final _model = TodoModel();

Future<void> _deleteTodo() async {
  _model.deleteAllTodo();
}

class _ListGradesPageState extends State<ListGradesPage> {
  //final _model = TodoModel();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
        actions: <Widget>[
          IconButton(
              icon: Icon(Icons.edit),
              onPressed: () {
                print('editing...');
                //_listTodos();
              }),
          IconButton(
              icon: Icon(Icons.delete),
              onPressed: () {
                print('deleting all...');
                setState(() {
                  _deleteTodo();
                });
              }),
        ],
      ),
      body: ListDisplayPage(),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          Navigator.push(
            context,
            MaterialPageRoute(builder: (context) => AddGrade()),
          );
        },
        child: Icon(Icons.add),
        backgroundColor: Colors.blue,
      ),
    );
  }
}

class ListDisplayPage extends StatefulWidget {
  ListDisplay createState() => ListDisplay();
}

class ListDisplay extends State<ListDisplayPage> {
  int _selectedIndex;

  List<Todo> todos = new List<Todo>();

  Future<void> _listTodos() async {
    todos = await _model.getAllTodos();

    if (todos.isEmpty) {
      print('it is empty-2.');
    } else {
      print("not empty-2");
    }

    print('To Dos:');
    for (Todo todo in todos) {
      print(todo);
    }
  }

  _onSelected(int index) {
    _selectedIndex = index;
  }

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


    _listTodos();

    // _listTodos() is not calling the function above for some reason, but executes everything below it
    // In the database there are items stored however it says the databse is empty...
    // until i add a new item and everything shows up except the item i recently added


    if (todos.isEmpty) {

      print('To Dos:');
      for (Todo todo in todos) {
        print(todo);
      }

      print('it is empty.');
    } else {
      print("not empty");
    }
  }

  @override
  Widget build(BuildContext context) {
    //Color clr = Colors.transparent;

    return todos.isEmpty
        ? Center(
            child: Text(
                'Nothing to show! Is it empty? ' + (todos.isEmpty).toString()))
        : ListView.builder(
            itemCount: todos.length,
            itemBuilder: (context, index) {
              return Card(
                //                           <-- Card widget
                child: Container(
                  color: _selectedIndex != null && _selectedIndex == index
                      ? Colors.lightBlueAccent
                      : Colors.transparent,
                  child: ListTile(
                    leading: GestureDetector(
                      onTap: () {
                        setState(() {
                          _onSelected(index);
                          print(index);
                        });
                      },
                      child: Container(

                        width: MediaQuery.of(context).size.width / 2,
                        child:
                            Text(todos[index].sid + '\n' + todos[index].grade),
                      ),
                    ),
                  ),
                ),
              );
            },
          );
  }
}

class AddGrade extends StatelessWidget {
  String _sid, _grade;

  final _formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Add Grade"),
      ),
      body: Form(
        key: _formKey,
        child: Column(
          children: <Widget>[
            Padding(
              padding: const EdgeInsets.all(15.0),
              child: TextFormField(
                decoration: const InputDecoration(
                  hintText: 'Student ID',
                  labelText: 'SID',
                ),
                onSaved: (String value) {
                  print('Saving SID $value');
                  _sid = value.toString();
                },
              ),
            ),
            Padding(
              padding: const EdgeInsets.all(15.0),
              child: TextFormField(
                decoration: const InputDecoration(
                  hintText: 'Student Grade',
                  labelText: 'Grade',
                ),
                onSaved: (String value) {
                  print('Saving Grade $value');
                  _grade = value.toString();
                },
              ),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          _formKey.currentState.save();
          _addTodo();
          //_listTodos();
          Navigator.pop(context);
        },
        child: Icon(Icons.save),
        backgroundColor: Colors.blue,
      ),
    );
  }

  Future<void> _addTodo() async {
    Todo newTodo = Todo(sid: _sid, grade: _grade);
    _lastInsertedId = await _model.insertTodo(newTodo);
  }
}

emulator的屏幕截图，添加新学生之前和添加新学生之后（在我再次添加另一个学生之前，最近的一个也不会显示）

如果我没有遵循指导原则，以前从未在这里发布过问题，我深表歉意。

你知道吗？我建议将您的

ListView.builder

包装到未来的生成器中，并将

\u loadTodos

函数作为未来的生成器传递。然后可以删除初始化TODO的所有initState代码

通常，我发现在

initState

中执行异步工作并不总是有效的。UI已经生成，不知道在异步工作完成时重建。另一个选项可能只是在异步函数完成TODO后调用

setState

。我认为FutureBuilder是更好的方法

如果你需要额外的帮助，请告诉我。我可能会给你写一些

Restarted application in 1,607ms.
I/flutter (14196): To Dos:
I/flutter (14196): it is empty.
I/flutter (14196): not empty-2
I/flutter (14196): To Dos:
I/flutter (14196): Todo{id: 1, sid: q, grade: qq}
I/flutter (14196): Todo{id: 2, sid: w, grade: ww}
I/flutter (14196): Todo{id: 3, sid: e, grade: ee}
I/flutter (14196): Todo{id: 4, sid: r, grade: }
I/flutter (14196): Todo{id: 5, sid: hh, grade: kk}