无法从SqFLite显示ListView

Question

我的数据能够无任何错误地上传到数据库，但是我似乎无法显示带有数据的列表视图。

[如从_submit()功能中看到的，如果出现错误，则会显示快餐栏，指示存在错误，并且不会进入主页，但是，结果显示带有成功消息的快餐栏，

所以我怀疑这与我的listview代码或我的databasehelper有关，因为我可能错过了代码中的某些内容。任何帮助深表感谢！

这里是我的列表视图代码：

FutureBuilder<List<Note>>(
  future: _databaseHelper.getNoteList(),
  builder: (BuildContext context, AsyncSnapshot<List<Note>> snapshot)
    if(snapshot.hasData)
       return  ListView.builder(
         itemCount: _count,
         itemBuilder: (BuildContext context, int position) 
           Note note = snapshot.data[position];
           return Card(
             color: Colors.white,
             elevation: 2.0,
             child: new ListTile(
               title: new Text(note.title),
               subtitle: new Text(note.bodyText),
               onTap: () =>
               _navigateToEditAddPage(note, 'Edit a Note'),
               onLongPress: () => _showDeleteDialog(note),
             ),
           );
        );
       else
         return Container(width: 0,height: 0,);
       
   ,),

这里是我的insertData代码：

void _submit() async 
  if (_formKey.currentState.validate()) 
    note.title = _titleController.text;
    note.bodyText = _bodyTextController.text;
    note.date = _dateController.text;
    if (note.id == null) 
      int result = await _databaseHelper.insertData(note);
      if (result != 0) 
        _moveToHomePage('Note successfully added');
       else 
          _showSnackBar('Note unable to be inserted due to some error');
        
       else 
          int result = await _databaseHelper.updateData(note);
          if (result != 0) 
            _moveToHomePage('Note successfully updated');
           else 
              _showSnackBar('Note unable to be updated due to some error');

这里是我的DatabaseHelper代码：

class DatabaseHelper 

  static Database _database;
  String dataTable = 'NoteTable';
  String colId = 'id';
  String colTitle = 'title';
  String colBody = 'bodyText';
  String colDate = 'date';

  DatabaseHelper._();
  static final DatabaseHelper db = DatabaseHelper._();

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

  Future<Database> initializeDatabase() async 
    Directory directory = await getApplicationDocumentsDirectory();
    String path = directory.path + 'notes.db';
    var notesDatabase =
        await openDatabase(path, version: 1, onCreate: _createDb);
    return notesDatabase;
  

  void _createDb(Database database, int newVersion) async 
    await database.execute("CREATE TABLE $dataTable ("
    "$colId INTEGER PRIMARY KEY AUTOINCREMENT,"
    "$colTitle TEXT,"
    "$colBody TEXT,"
    "$colDate TEXT"
    ")");
  

  Future<List<Map<String, dynamic>>> getNoteListMap() async 
    Database db = await this.database;
    var result = await db.query(dataTable);
    return result;
  

  Future<int> insertData(Note note) async 
    Database db = await this.database;
    var result = await db.insert(dataTable,note.toMap(),conflictAlgorithm: 
    ConflictAlgorithm.replace,);
    return result;
  

  Future<int> updateData(Note note) async 
    Database db = await this.database;
    var result = await db.update(dataTable,note.toMap(),
        where: 'colId = ?', whereArgs: [note.id]);
    return result;
  

  Future<int> deleteData(Note note) async 
    Database db = await this.database;
    var result = await db
        .delete(dataTable, where: 'colId = ?', whereArgs: [note.id]);
    return result;
  

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

  Future<List<Note>> getNoteList() async 
    var noteMapList = await getNoteListMap();
    int count = noteMapList.length;
    //list of notes, each note consist of their own independent variables
    List<Note> noteList;
    for (int i = 0; i < count; i++) 
      noteList.add(Note.fromMapObject(noteMapList[i]));
    
    return noteList;

最后是我的Note模型：

class Note 
  int _id;
  String _date;
  String _title;
  String _bodyText;
  Note(this._date, this._title, this._bodyText);
  Note.withId(this._id, this._date, this._title, this._bodyText);

  set date(String date) 
    this._date = date;
  

  get date => _date;

  set title(String title) 
    this._title = title;
  

  get title => _title;

  set bodyText(String bodyText)
    this._bodyText = bodyText;
  

  get bodyText => _bodyText;

  get id => _id;

  Map<String, dynamic> toMap() 
    var map = new Map<String, dynamic>();
    if (_id != null) 
      map['id'] = _id;
    
    map['title'] = _title;
    map['bodyText'] = _bodyText;
    map['date'] = _date;
    return map;
  

//Converting a map object to a note object
  Note.fromMapObject(Map<String,dynamic> fromMap)
    _id = fromMap['id'];
    _title = fromMap['title'];
    _bodyText = fromMap['bodyText'];
    _date = fromMap['date'];