flutter 如何让我的代码与监听器或回调一起工作？ （编辑）

Question

我想要实现的是，当我在 WelcomeScreen 类中添加新食物时，我希望在 FoodList 类中重新呈现我的食物对象列表。下面我有两个类的相关代码。我的问题似乎是当我添加一个新对象时 FoodList 类没有呈现！？我尝试对 FoodList 使用 ChangeNotifierProvider，并从 WelcomeScreen 调用 setFoodList 方法，该方法调用 notifyListeners 方法，但它似乎不起作用。

代码逻辑应该是应用程序从一开始就加载应用程序中的图像，然后用户应该能够使用图像选择器添加图像，这些图像也被保存到数据库中。

非常感谢任何想法！

我的相关代码是。

FoodList类：

getChildrenOfFoodBrainList(List<Food> foodList) {
    //final foodList = Provider.of<FoodBrain>(context).getFoodList();
    return List.of(foodList.map((food) => ImageCircle(
          image: food.imageDb == null ? food.fileName! : food.imageDb!,
          displayName: food.displayName!,
          text: food.text,
        )));
  }

  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      create: (context) => FoodBrain(),
      child: Scaffold(
          backgroundColor: Colors.white,
          body: SafeArea(
            child: Consumer<FoodBrain>(builder: (context, foodBrain, _) {
              return Column(children: <Widget>[
                AppBar(
                  backgroundColor: Colors.grey,
                  actions: [
                    IconButton(onPressed: () {}, icon: Icon(Icons.search)),
                  ],
                ),
                   
                Expanded(
                  child: Center(
                    
                    child: GridView.count(
                      primary: false,
                      crossAxisCount: 4,
                      shrinkWrap: true,
                      
                      
                      children:
                          getChildrenOfFoodBrainList(foodBrain.getFoodList()),
                    ),
                  ),
                ),

欢迎屏幕类：

Future<File?> saveImageToDatabase(_displayName, imageFile) async {
    final file = File(imageFile!.path);
    String imgString = Utility.base64String(file.readAsBytesSync());

//Create new food object
    setState(() {
      Food food = new Food(
          displayName: _displayName,
          fileName: null,
          imageDb: imgString,
          text: null);

      //Save food image to database
      dbHelper.save(food);

      //Add food to FoodList
      brain.addFoodToList(food);
      
      //call notifylistener from FoodBrain class
      brain.setFoodList(brain.getFoodList());
      

      print(brain.getDisplayName());
    });

    
  }

这是从欢迎屏幕运行保存图像的代码：

//Value passed from userInput
  _imageFile = imageFile;
                                                  
   await saveImageToDatabase(
     _displayName, imageFile);
   Navigator.of(context).pop();  

                                           

食脑类： 使用通知监听器的类

 void setFoodList(List<Food> newList) {
    _foodList = newList;
    notifyListeners();
  }          

DBHelper类： 初始化并使用各种方法进行数据库连接的类。

class DBHelper {

  static Database? _db;
  static const String ID = 'id';
  //static const String Path = 'path';
  static const String Name = 'displayName';
  static const String TABLE = 'photosTable';
  static const String ImageDb = 'imageDb';
  static const String DB_NAME = 'photos.db';

  Future<Database> get db async {
    if (_db != null) {
      return _db!;
    }
    _db = await initDB();
    return _db!;
  }

  initDB() async {
    io.Directory documentsDirectory = await getApplicationDocumentsDirectory();
    String path = join(documentsDirectory.path, DB_NAME);
    var db = await openDatabase(path, version: 1, onCreate: _onCreate);
    return db;
  }

  _onCreate(Database db, int version) async {
    await db.execute(
        'CREATE TABLE $TABLE ($ID INTEGER, $Name TEXT, $ImageDb TEXT)');
  }

  Future<Food> save(Food food) async {
    var dbClient = await db;
    food.id = await dbClient.insert(TABLE, food.toMap());
    return food;
  }

  //Get all photos from db
  Future<List<Food>> getPhotos() async {
    var dbClient = await db;
    List<Map> maps = await dbClient.query(TABLE, columns: [ID, Name, ImageDb]);
    List<Food> photos = [];
    if (maps.length > 0) {
      for (int i = 0; i < maps.length; i++) {
        photos.add(Food.fromMap(maps[i]));
      }
    }
    return photos;
  }

  Future close() async {
    var dbClient = await db;
    dbClient.close();
  }
}

ImageCircle类：
这个类正在显示图像。来自数据库或本地存储。

Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(10.0),
      child: Material(
        elevation: 10.0,
        shape: CircleBorder(),
        clipBehavior: Clip.hardEdge,
        color: Colors.transparent,
        //Here we check if its a String or database file image and convert to image
        child: Ink.image(
          image: widget.image is String
              ? Image.asset(widget.image).image
              : Utility.imageFromBase64String(widget.image).image,
          fit: BoxFit.cover,
          width: 90.0,
          height: 90.0,
          child: InkWell(
            onTap: () {
              setState(() {
                getImageToMapList(widget.image, widget.displayName);

                //Hide current snackbar on Click if exists. Maybe we need an if exists also?
                ScaffoldMessenger.of(context).hideCurrentSnackBar();
                getSnackBar();
              });
            },
            //check on lesson about value and how to use it (animations?)
            //Hmm hover does not exist on a phone? only when you have a mouse?
          ),
        ),
      ),
    );
  }
}

附言。我现在已经编辑了更多的课程。

Answer 1

通常它应该工作， 需要知道这堂课发生了什么

//Save food image to database
      dbHelper.save(food);

      //Add food to FoodList
      brain.addFoodToList(food);
      
      //call notifylistener from FoodBrain class
      brain.setFoodList(brain.getFoodList());