Question

我无法从数据库填充DropDown。

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

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

Future<List<Project>> getProjectsList() async {

var projectsMapList = await getProjectsMapList(); // Get 'Map List' from database
int count = projectsMapList.length;         // Count the number of map entries in db table

List<Project> projectList = List<Project>();
// For loop to create a 'categories List' from a 'Map List'
for (int i = 0; i < count; i++) {
  projectList.add(Project.fromMapObject(projectsMapList[i]));
}
return projectList;
}

我在其中创建了DropDown的项目类，但下拉菜单中没有显示任何值。

Project projectModel;
List<Project> newList = <Project> [];
@override
  void initState() {
    super.initState();
    _getProjectList();

  }
  void _getProjectList() async {
    final List<Project> _listPj = await databaseHelper.getProjectsList();
    setState(() {
      newList = _listPj;
    });
  }

DropDown

               DropdownButtonFormField<Project>(
               hint: Text('Project'),
               value: projectModel,
               onChanged: (Project value){
                 setState(() {
                   projectModel = value;
                 });
               },

               items: newList.map((project) => DropdownMenuItem<Project>(
                 child: Text(projectModel.title),
                 value: project,
               )
               ).toList()
           ),

模型类


  int _id;
  String _title;
  String _date;



  Project(this._title, this._date);

  int get id => _id;

  String get title => _title;

  String get date => _date;


  set id(int value) {
    this._id = value;
  }

  set title(String newTitle) {
    if (newTitle.length <= 255) {
      this._title = newTitle;
    }
  }


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

  // Convert a Note object into a Map object
  Map<String, dynamic> toMap() {

    var map = Map<String, dynamic>();
    if (id != null) {
      map['id'] = _id;
    }
    map['title'] = _title;

    map['date'] = _date;


    return map;
  }

  // Extract a Note object from a Map object
  Project.fromMapObject(Map<String, dynamic> map) {
    this._id = map['id'];
    this._title = map['title'];
    this._date = map['date'];

  }
}

这是代码，但是我不明白为什么下拉列表中没有显示数据？有人可以帮助我吗？我收到NoSuchMethodError：在NULL上调用了吸气剂“ title”，但我不知道我在哪里做过miatake？

Answer 1

请将 child: Text(projectModel.title) 改为 child: Text(project.title)

           items: newList.map((project) => DropdownMenuItem<Project>(
             child: Text(project.title),
             value: project,
           )
           ).toList()

如何使用sqflite填充下拉菜单？

1 个答案: