Flutter 吸气剂'；名称'；被调用为空_Flutter_Dart

Flutter 吸气剂'；名称'；被调用为空

flutter dart

Flutter 吸气剂'；名称'；被调用为空,flutter,dart,Flutter,Dart,我正在尝试制作一个与简单的todo应用程序具有基本相同的机制的应用程序。我的问题是，当我试图打开可以创建新项目/todo（new_project_screen）的屏幕时，应该会加载一些文本字段，但它们不会。相反，会发生此错误。我尝试了stackoverflow的几种解决方案，但都不起作用，我也不知道为什么它不起作用这是我的密码： main.dart: import 'package:flutter/material.dart'; import 'package:leisy/surface/ma

我正在尝试制作一个与简单的todo应用程序具有基本相同的机制的应用程序。我的问题是，当我试图打开可以创建新项目/todo（new_project_screen）的屏幕时，应该会加载一些文本字段，但它们不会。相反，会发生此错误。我尝试了stackoverflow的几种解决方案，但都不起作用，我也不知道为什么它不起作用

这是我的密码： main.dart:

import 'package:flutter/material.dart';
import 'package:leisy/surface/main_screen.dart';

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(App());
}

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Leisy',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MainScreen(),
    );
  }
}

import 'package:flutter/material.dart';
import 'dart:async';

import 'package:sqflite/sqflite.dart';

import 'package:leisy/db/database_helper.dart';
import 'package:leisy/model/project.dart';
import 'package:leisy/surface/settings_screen.dart';
import 'package:leisy/surface/new_project_screen.dart';

class MainScreen extends StatefulWidget {
  @override
  _MainScreenState createState() => _MainScreenState();
}

class _MainScreenState extends State<MainScreen> {
  DatabaseHelper databaseHelper = DatabaseHelper();
  List<Project> projectList = [];
  int count = 0;

  @override
  Widget build(BuildContext context) {
    if (projectList == null) {
      projectList = <Project>[];
      updateListView();
    }
    debugPrint("Building entire main screen scaffold");
    return Scaffold(
      appBar: AppBar(
        title: Text("Leisy"),
      ),
      drawer: Drawer(
        child: ListView(
          padding: EdgeInsets.zero,
          children: <Widget>[
            DrawerHeader(
              child: Center(
                child: Text(
                  "Menü",
                  textAlign: TextAlign.center,
                  style: TextStyle(
                    color: Colors.white,
                    fontSize: 25,
                  ),
                ),
              ),
              decoration: BoxDecoration(color: Colors.blue),
            ),
            ListTile(
              leading: Icon(Icons.home),
              title: Text('Home'),
              onTap: () => {Navigator.of(context).pop()},
            ),
            ListTile(
              leading: Icon(Icons.add),
              title: Text('Neues Projekt'),
              onTap: () => {
                Navigator.of(context).push(new MaterialPageRoute(
                    builder: (context) => new NewProjectScreen()))
              },
            ),
            ListTile(
              leading: Icon(Icons.settings),
              title: Text('Einstellungen'),
              onTap: () => {
                Navigator.of(context).push(
                    MaterialPageRoute(builder: (context) => SettingsScreen()))
              },
            )
          ],
        ),
      ),
      body: getProjectListView(),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: navigateToNewProject,
      ),
    );
  }

  ListView getProjectListView() {
    TextStyle titleStyle = Theme.of(context).textTheme.subtitle1;

    return ListView.builder(
        itemCount: count,
        itemBuilder: (BuildContext context, int position) {
          return Card(
            color: Colors.white,
            elevation: 2.0,
            child: ListTile(
              leading: CircleAvatar(
                backgroundColor: Colors.blue,
              ),
              title: Text(
                this.projectList[position].name,
                style: titleStyle,
              ),
              subtitle: Text(this.projectList[position].date),
              onTap: () {
                debugPrint('ListTile Tapped');
                //navigateToDetail() einfügen
              },
            ),
          );
        });
  }

  void _showSnackBar(BuildContext context, String message) {
    final snackBar = SnackBar(
      content: Text(message),
    );
    ScaffoldMessenger.of(context).showSnackBar(snackBar);
  }

  void navigateToNewProject() async {
    bool result = await Navigator.push(context, MaterialPageRoute(builder: (context) => NewProjectScreen()));

    if (result == true) {
      updateListView();
    }
  }

  void updateListView() {
    final Future<Database> dbFuture = databaseHelper.initDB();
    dbFuture.then((database) {
      Future<List<Project>> projectListFuture = databaseHelper.getProjectList();
      projectListFuture.then((projectList) {
        setState(() {
          this.projectList = projectList;
          this.count = projectList.length;
        });
      });
    });
  }
}

import 'package:flutter/material.dart';
import 'package:leisy/db/database_helper.dart';
import 'package:leisy/model/project.dart';

import 'package:leisy/surface/main_screen.dart';
import 'package:leisy/surface/settings_screen.dart';

class NewProjectScreen extends StatefulWidget {
  @override
  _NewProjectScreenState createState() => _NewProjectScreenState();
}

class _NewProjectScreenState extends State<NewProjectScreen> {
  Project project;

  DatabaseHelper helper = DatabaseHelper();

  TextEditingController nameController = TextEditingController();
  TextEditingController dateController = TextEditingController();
  TextEditingController locationController = TextEditingController();

  @override
  Widget build(BuildContext context) {
    nameController.text = project.name;
    dateController.text = project.date;
    locationController.text = project.location;

    return Scaffold(
        appBar: AppBar(
          title: Text("Neues Projekt"),
          leading: IconButton(
            icon: Icon(Icons.arrow_back),
            onPressed: () {
              Navigator.pop(context);
            },
          ),
        ),
        drawer: Drawer(
          child: ListView(
            padding: EdgeInsets.zero,
            children: <Widget>[
              DrawerHeader(
                child: Center(
                  child: Text(
                    "Menü",
                    textAlign: TextAlign.center,
                    style: TextStyle(
                      color: Colors.white,
                      fontSize: 25,
                    ),
                  ),
                ),
                decoration: BoxDecoration(color: Colors.blue),
              ),
              ListTile(
                leading: Icon(Icons.home),
                title: Text('Home'),
                onTap: () => {
                  Navigator.of(context).push(
                      MaterialPageRoute(builder: (context) => MainScreen()))
                },
              ),
              ListTile(
                leading: Icon(Icons.add),
                title: Text('Neues Projekt'),
                onTap: () => {Navigator.of(context).pop()},
              ),
              ListTile(
                leading: Icon(Icons.settings),
                title: Text('Einstellungen'),
                onTap: () => {
                  Navigator.of(context).push(
                      MaterialPageRoute(builder: (context) => SettingsScreen()))
                },
              )
            ],
          ),
        ),
        body: Padding(
            padding: EdgeInsets.all(8.0),
            child: ListView(
              children: <Widget>[
                TextField(
                  controller: nameController,
                  decoration: InputDecoration(labelText: 'Name'),
                  style: TextStyle(fontSize: 20),
                  onChanged: (value) {
                    setState(() {
                      updateName();
                    });
                  },
                ),
                TextField(
                  decoration: InputDecoration(labelText: 'Datum'),
                  style: TextStyle(fontSize: 20),
                  onChanged: (value) {
                    setState(() {
                      updateDate();
                    });
                  },
                ),
                TextField(
                  decoration: InputDecoration(labelText: 'Ort'),
                  style: TextStyle(fontSize: 20),
                  onChanged: (value) {
                    setState(() {
                      updateLocation();
                    });
                  },
                ),
                Row(
                  children: <Widget>[
                    Expanded(
                        child: ElevatedButton(
                          style: ButtonStyle(
                            backgroundColor: MaterialStateProperty.all(
                                Theme.of(context).primaryColorDark),
                          ),
                          child: Text('Speichern'),
                          onPressed: () {
                            setState(() {
                              _save();
                            });
                          },
                        )),
                    Expanded(
                        child: ElevatedButton(
                          style: ButtonStyle(
                            backgroundColor: MaterialStateProperty.all(
                                Theme.of(context).primaryColorDark),
                          ),
                          child: Text('Abbrechen'),
                          onPressed: () {
                            setState(() {
                              _cancel();
                            });
                          },
                        )),
                  ],
                )
              ],
            )
        )
    );
  }

  void _save() async {
    Navigator.pop(context, true);

    await helper.insertProject(project);
  }

  void _showSnackBar(String message) {
    SnackBar snackBar = SnackBar(content: Text(message));
    ScaffoldMessenger.of(context).showSnackBar(snackBar);
  }

  void _cancel() async {
    Navigator.pop(context, true);

    _showSnackBar('Vorgang abgebrochen');
  }

  void updateName() {
    project.name = nameController.text;
  }

  void updateDate() {
    project.date = dateController.text;
  }

  void updateLocation() {
    project.location = locationController.text;
  }
}

class Project {
  int _id;
  String _name;
  String _date;
  String _location;
  String _personaldb;

  Project(this._name, this._date, this._location, this._personaldb);
  Project.withId(
      this._id, this._name, this._date, this._location, this._personaldb);

  int get id => _id;
  String get name => _name;
  String get date => _date;
  String get location => _location;
  String get personalDB => _personaldb;

  set name(String newName) {
    if (newName.length <= 63) {
      this._name = newName;
    }
  }

  set date(String newDate) {
    this._date = newDate;
  }

  set location(String newLocation) {
    this._location = newLocation;
  }

  set personalDB(String newPersonalDB) {
    this._personaldb = newPersonalDB;
  }

  Map<String, dynamic> toMap() {
    var map = Map<String, dynamic>();
    if (id != null) {
      map['id'] = _id;
    }
    map['name'] = _name;
    map['date'] = _date;
    map['location'] = _location;
    map['personalDB'] = _personaldb;

    return map;
  }

  Project.fromMapObject(Map<String, dynamic> map) {
    this._id = map['id'];
    this._name = map['name'];
    this._date = map['date'];
    this._location = map['location'];
    this._personaldb = map['personalDB'];
  }
}

import 'dart:async';
import 'dart:io';

import 'package:path_provider/path_provider.dart';
import 'package:sqflite/sqflite.dart';

import 'package:leisy/model/project.dart';

class DatabaseHelper {

  static DatabaseHelper _databaseHelper;
  static Database _database;

  String projectTable = 'project_table';
  String colId = 'id';
  String colName = 'name';
  String colDate = 'date';
  String colLocation = 'location';
  String colPersonalDB = 'personalDB';

  DatabaseHelper._createInstance();

  factory DatabaseHelper() {
    if (_databaseHelper == null) {
      _databaseHelper = DatabaseHelper._createInstance();
    }
    return _databaseHelper;
  }

  Future<Database> get database async {
    if (_database == null) {
      _database = await initDB();
    }
    return _database;
  }

  Future<Database> initDB() async {
    Directory directory = await getApplicationDocumentsDirectory();
    String path = directory.path + 'projects.db';

    var projectsDB = await openDatabase(path, version:  1, onCreate: _createDB);
    return projectsDB;
  }

  void _createDB(Database db, int newVersion) async {

    await db.execute('CREATE TABLE $projectTable('
        '$colId INTEGER PRIMARY KEY AUTOINCREMENT,'
        '$colName TEXT,'
        '$colDate TEXT,'
        '$colLocation TEXT,'
        '$colPersonalDB TEXT)');
  }

  Future<List<Map<String, dynamic>>> getProjectMapList() async {
    Database db = await this.database;

    var result = await db.query(projectTable);
    return result;
  }

  Future<int> insertProject(Project project) async {
    Database db = await this.database;
    var result = await db.insert(projectTable, project.toMap());
    return result;
  }

  Future<int> updateProject(Project project) async {
    var db = await this.database;
    var result = await db.update(projectTable, project.toMap(), where: '$colId = ?', whereArgs: [project.id]);
    return result;
  }

  Future<int> deleteProject(int id) async {
    var db = await this.database;
    int result = await db.delete(projectTable, where: '$colId = $id');
    return result;
  }

  Future<int> getCount() async {
    Database db = await this.database;
    List<Map<String, dynamic>> x = await db.rawQuery('SELECT COUNT (*) from $projectTable');
    int result = Sqflite.firstIntValue(x);
    return result;
  }

  Future<List<Project>> getProjectList() async {
    var projectMapList = await getProjectMapList();
    int count = projectMapList.length;

    List<Project> projectList = <Project>[];

    for (int i = 0; i < count; i++) {
      projectList.add(Project.fromMapObject(projectMapList[i]));
    }
    return projectList;
  }
}

======== Exception caught by widgets library =======================================================
The following NoSuchMethodError was thrown building NewProjectScreen(dirty, state: _NewProjectScreenState#670bc):
The getter 'name' was called on null.
Receiver: null
Tried calling: name

The relevant error-causing widget was: 
  NewProjectScreen file:///C:/Users/gabri/AndroidStudioProjects/leisy/lib/surface/main_screen.dart:116:89
When the exception was thrown, this was the stack: 
#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
#1      _NewProjectScreenState.build (package:leisy/surface/new_project_screen.dart:24:35)
#2      StatefulElement.build (package:flutter/src/widgets/framework.dart:4612:27)
#3      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4495:15)
#4      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4667:11)
...
====================================================================================================

主屏幕。省道：

import 'package:flutter/material.dart';
import 'package:leisy/surface/main_screen.dart';

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(App());
}

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Leisy',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MainScreen(),
    );
  }
}

import 'package:flutter/material.dart';
import 'dart:async';

import 'package:sqflite/sqflite.dart';

import 'package:leisy/db/database_helper.dart';
import 'package:leisy/model/project.dart';
import 'package:leisy/surface/settings_screen.dart';
import 'package:leisy/surface/new_project_screen.dart';

class MainScreen extends StatefulWidget {
  @override
  _MainScreenState createState() => _MainScreenState();
}

class _MainScreenState extends State<MainScreen> {
  DatabaseHelper databaseHelper = DatabaseHelper();
  List<Project> projectList = [];
  int count = 0;

  @override
  Widget build(BuildContext context) {
    if (projectList == null) {
      projectList = <Project>[];
      updateListView();
    }
    debugPrint("Building entire main screen scaffold");
    return Scaffold(
      appBar: AppBar(
        title: Text("Leisy"),
      ),
      drawer: Drawer(
        child: ListView(
          padding: EdgeInsets.zero,
          children: <Widget>[
            DrawerHeader(
              child: Center(
                child: Text(
                  "Menü",
                  textAlign: TextAlign.center,
                  style: TextStyle(
                    color: Colors.white,
                    fontSize: 25,
                  ),
                ),
              ),
              decoration: BoxDecoration(color: Colors.blue),
            ),
            ListTile(
              leading: Icon(Icons.home),
              title: Text('Home'),
              onTap: () => {Navigator.of(context).pop()},
            ),
            ListTile(
              leading: Icon(Icons.add),
              title: Text('Neues Projekt'),
              onTap: () => {
                Navigator.of(context).push(new MaterialPageRoute(
                    builder: (context) => new NewProjectScreen()))
              },
            ),
            ListTile(
              leading: Icon(Icons.settings),
              title: Text('Einstellungen'),
              onTap: () => {
                Navigator.of(context).push(
                    MaterialPageRoute(builder: (context) => SettingsScreen()))
              },
            )
          ],
        ),
      ),
      body: getProjectListView(),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: navigateToNewProject,
      ),
    );
  }

  ListView getProjectListView() {
    TextStyle titleStyle = Theme.of(context).textTheme.subtitle1;

    return ListView.builder(
        itemCount: count,
        itemBuilder: (BuildContext context, int position) {
          return Card(
            color: Colors.white,
            elevation: 2.0,
            child: ListTile(
              leading: CircleAvatar(
                backgroundColor: Colors.blue,
              ),
              title: Text(
                this.projectList[position].name,
                style: titleStyle,
              ),
              subtitle: Text(this.projectList[position].date),
              onTap: () {
                debugPrint('ListTile Tapped');
                //navigateToDetail() einfügen
              },
            ),
          );
        });
  }

  void _showSnackBar(BuildContext context, String message) {
    final snackBar = SnackBar(
      content: Text(message),
    );
    ScaffoldMessenger.of(context).showSnackBar(snackBar);
  }

  void navigateToNewProject() async {
    bool result = await Navigator.push(context, MaterialPageRoute(builder: (context) => NewProjectScreen()));

    if (result == true) {
      updateListView();
    }
  }

  void updateListView() {
    final Future<Database> dbFuture = databaseHelper.initDB();
    dbFuture.then((database) {
      Future<List<Project>> projectListFuture = databaseHelper.getProjectList();
      projectListFuture.then((projectList) {
        setState(() {
          this.projectList = projectList;
          this.count = projectList.length;
        });
      });
    });
  }
}

import 'package:flutter/material.dart';
import 'package:leisy/db/database_helper.dart';
import 'package:leisy/model/project.dart';

import 'package:leisy/surface/main_screen.dart';
import 'package:leisy/surface/settings_screen.dart';

class NewProjectScreen extends StatefulWidget {
  @override
  _NewProjectScreenState createState() => _NewProjectScreenState();
}

class _NewProjectScreenState extends State<NewProjectScreen> {
  Project project;

  DatabaseHelper helper = DatabaseHelper();

  TextEditingController nameController = TextEditingController();
  TextEditingController dateController = TextEditingController();
  TextEditingController locationController = TextEditingController();

  @override
  Widget build(BuildContext context) {
    nameController.text = project.name;
    dateController.text = project.date;
    locationController.text = project.location;

    return Scaffold(
        appBar: AppBar(
          title: Text("Neues Projekt"),
          leading: IconButton(
            icon: Icon(Icons.arrow_back),
            onPressed: () {
              Navigator.pop(context);
            },
          ),
        ),
        drawer: Drawer(
          child: ListView(
            padding: EdgeInsets.zero,
            children: <Widget>[
              DrawerHeader(
                child: Center(
                  child: Text(
                    "Menü",
                    textAlign: TextAlign.center,
                    style: TextStyle(
                      color: Colors.white,
                      fontSize: 25,
                    ),
                  ),
                ),
                decoration: BoxDecoration(color: Colors.blue),
              ),
              ListTile(
                leading: Icon(Icons.home),
                title: Text('Home'),
                onTap: () => {
                  Navigator.of(context).push(
                      MaterialPageRoute(builder: (context) => MainScreen()))
                },
              ),
              ListTile(
                leading: Icon(Icons.add),
                title: Text('Neues Projekt'),
                onTap: () => {Navigator.of(context).pop()},
              ),
              ListTile(
                leading: Icon(Icons.settings),
                title: Text('Einstellungen'),
                onTap: () => {
                  Navigator.of(context).push(
                      MaterialPageRoute(builder: (context) => SettingsScreen()))
                },
              )
            ],
          ),
        ),
        body: Padding(
            padding: EdgeInsets.all(8.0),
            child: ListView(
              children: <Widget>[
                TextField(
                  controller: nameController,
                  decoration: InputDecoration(labelText: 'Name'),
                  style: TextStyle(fontSize: 20),
                  onChanged: (value) {
                    setState(() {
                      updateName();
                    });
                  },
                ),
                TextField(
                  decoration: InputDecoration(labelText: 'Datum'),
                  style: TextStyle(fontSize: 20),
                  onChanged: (value) {
                    setState(() {
                      updateDate();
                    });
                  },
                ),
                TextField(
                  decoration: InputDecoration(labelText: 'Ort'),
                  style: TextStyle(fontSize: 20),
                  onChanged: (value) {
                    setState(() {
                      updateLocation();
                    });
                  },
                ),
                Row(
                  children: <Widget>[
                    Expanded(
                        child: ElevatedButton(
                          style: ButtonStyle(
                            backgroundColor: MaterialStateProperty.all(
                                Theme.of(context).primaryColorDark),
                          ),
                          child: Text('Speichern'),
                          onPressed: () {
                            setState(() {
                              _save();
                            });
                          },
                        )),
                    Expanded(
                        child: ElevatedButton(
                          style: ButtonStyle(
                            backgroundColor: MaterialStateProperty.all(
                                Theme.of(context).primaryColorDark),
                          ),
                          child: Text('Abbrechen'),
                          onPressed: () {
                            setState(() {
                              _cancel();
                            });
                          },
                        )),
                  ],
                )
              ],
            )
        )
    );
  }

  void _save() async {
    Navigator.pop(context, true);

    await helper.insertProject(project);
  }

  void _showSnackBar(String message) {
    SnackBar snackBar = SnackBar(content: Text(message));
    ScaffoldMessenger.of(context).showSnackBar(snackBar);
  }

  void _cancel() async {
    Navigator.pop(context, true);

    _showSnackBar('Vorgang abgebrochen');
  }

  void updateName() {
    project.name = nameController.text;
  }

  void updateDate() {
    project.date = dateController.text;
  }

  void updateLocation() {
    project.location = locationController.text;
  }
}

class Project {
  int _id;
  String _name;
  String _date;
  String _location;
  String _personaldb;

  Project(this._name, this._date, this._location, this._personaldb);
  Project.withId(
      this._id, this._name, this._date, this._location, this._personaldb);

  int get id => _id;
  String get name => _name;
  String get date => _date;
  String get location => _location;
  String get personalDB => _personaldb;

  set name(String newName) {
    if (newName.length <= 63) {
      this._name = newName;
    }
  }

  set date(String newDate) {
    this._date = newDate;
  }

  set location(String newLocation) {
    this._location = newLocation;
  }

  set personalDB(String newPersonalDB) {
    this._personaldb = newPersonalDB;
  }

  Map<String, dynamic> toMap() {
    var map = Map<String, dynamic>();
    if (id != null) {
      map['id'] = _id;
    }
    map['name'] = _name;
    map['date'] = _date;
    map['location'] = _location;
    map['personalDB'] = _personaldb;

    return map;
  }

  Project.fromMapObject(Map<String, dynamic> map) {
    this._id = map['id'];
    this._name = map['name'];
    this._date = map['date'];
    this._location = map['location'];
    this._personaldb = map['personalDB'];
  }
}

import 'dart:async';
import 'dart:io';

import 'package:path_provider/path_provider.dart';
import 'package:sqflite/sqflite.dart';

import 'package:leisy/model/project.dart';

class DatabaseHelper {

  static DatabaseHelper _databaseHelper;
  static Database _database;

  String projectTable = 'project_table';
  String colId = 'id';
  String colName = 'name';
  String colDate = 'date';
  String colLocation = 'location';
  String colPersonalDB = 'personalDB';

  DatabaseHelper._createInstance();

  factory DatabaseHelper() {
    if (_databaseHelper == null) {
      _databaseHelper = DatabaseHelper._createInstance();
    }
    return _databaseHelper;
  }

  Future<Database> get database async {
    if (_database == null) {
      _database = await initDB();
    }
    return _database;
  }

  Future<Database> initDB() async {
    Directory directory = await getApplicationDocumentsDirectory();
    String path = directory.path + 'projects.db';

    var projectsDB = await openDatabase(path, version:  1, onCreate: _createDB);
    return projectsDB;
  }

  void _createDB(Database db, int newVersion) async {

    await db.execute('CREATE TABLE $projectTable('
        '$colId INTEGER PRIMARY KEY AUTOINCREMENT,'
        '$colName TEXT,'
        '$colDate TEXT,'
        '$colLocation TEXT,'
        '$colPersonalDB TEXT)');
  }

  Future<List<Map<String, dynamic>>> getProjectMapList() async {
    Database db = await this.database;

    var result = await db.query(projectTable);
    return result;
  }

  Future<int> insertProject(Project project) async {
    Database db = await this.database;
    var result = await db.insert(projectTable, project.toMap());
    return result;
  }

  Future<int> updateProject(Project project) async {
    var db = await this.database;
    var result = await db.update(projectTable, project.toMap(), where: '$colId = ?', whereArgs: [project.id]);
    return result;
  }

  Future<int> deleteProject(int id) async {
    var db = await this.database;
    int result = await db.delete(projectTable, where: '$colId = $id');
    return result;
  }

  Future<int> getCount() async {
    Database db = await this.database;
    List<Map<String, dynamic>> x = await db.rawQuery('SELECT COUNT (*) from $projectTable');
    int result = Sqflite.firstIntValue(x);
    return result;
  }

  Future<List<Project>> getProjectList() async {
    var projectMapList = await getProjectMapList();
    int count = projectMapList.length;

    List<Project> projectList = <Project>[];

    for (int i = 0; i < count; i++) {
      projectList.add(Project.fromMapObject(projectMapList[i]));
    }
    return projectList;
  }
}

======== Exception caught by widgets library =======================================================
The following NoSuchMethodError was thrown building NewProjectScreen(dirty, state: _NewProjectScreenState#670bc):
The getter 'name' was called on null.
Receiver: null
Tried calling: name

The relevant error-causing widget was: 
  NewProjectScreen file:///C:/Users/gabri/AndroidStudioProjects/leisy/lib/surface/main_screen.dart:116:89
When the exception was thrown, this was the stack: 
#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
#1      _NewProjectScreenState.build (package:leisy/surface/new_project_screen.dart:24:35)
#2      StatefulElement.build (package:flutter/src/widgets/framework.dart:4612:27)
#3      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4495:15)
#4      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4667:11)
...
====================================================================================================

如果有人能帮助我，我将非常感激。如果我的代码中有任何地方不方便或实现不好，请对我好一点，我是这方面的初学者。

文件新建项目屏幕。dart有问题

确切地说，问题可以在第24:35行中找到

项目变量似乎为null

project.name
这是因为您正在创建项目，但尚未实例化。只是一个空变量
请参见下图，这将有助于您了解一点：


因此，要修复它，您需要先创建实例
非常感谢。成功了！没想到会这么容易…嗨！不客气！你的问题很清楚，但太长了。它有与问题无关的代码。下次请说得更具体些。谢谢