list - 如何从列表内部访问实例方法？

Question

所以，我试图按类的特定方法对列表进行分组排序。我的代码目前以此类格式使用 Hive 存储“膳食”:
https://pub.dev/packages/hive

import 'package:hive/hive.dart';

part 'meal.g.dart';

@HiveType(typeId: 1, adapterName: "MealAdapter")
class MealModel{
  @HiveField(0)
  int id;
  @HiveField(1)
  String mealName;
  @HiveField(2)
  int calories;
  @HiveField(3)
  int carbohydrates;
  @HiveField(4)
  int protein;
  @HiveField(5)
  int fats;
  @HiveField(6)
  String day;

  MealModel(this.id, this.mealName, this.calories, this.day, [this.carbohydrates, this.protein, this.fats]);
}

问题是当我不知道我会将值传递给 GroupedListView ( https://pub.dev/packages/grouped_list ) 的每个参数以显示存储的饭菜时:

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:hive/hive.dart';
import 'package:jaetrack/colors.dart';
import 'package:jaetrack/dbmodel/meal.dart';
import 'package:hive_flutter/hive_flutter.dart';
import 'package:grouped_list/grouped_list.dart';

class Meals extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return MealsState();
  }
}

class MealsState extends State<Meals> {
  Box<MealModel> mealBox = Hive.box<MealModel>('meals');
  MealModel previousMeal;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: mainPurp,
      body: SingleChildScrollView(
        child: Column(
          children: [
            ValueListenableBuilder(
                valueListenable: Hive.box<MealModel>('meals').listenable(),
                builder: (context, Box<MealModel> box, _) {
                  final mealList = box.values.toList().cast<MealModel>();
                  print(mealList);
                  return GroupedListView<dynamic, String>(
                    elements: mealList,
                    groupBy: (meal) => meal, // no idea how to sort by calories, name etc. of my MealModel class,
                    groupSeparatorBuilder: (String groupByValue) =>
                        Text(groupByValue), // date value
                    itemBuilder: (context, dynamic element) =>
                        Text(element['name']), // this is where I would put the meal names/calories etc.
                    itemComparator: (item1, item2) =>
                        item1['name'].compareTo(item2['name']), // sort by date is what I'm looking for but again I don't know how to access
                    useStickyGroupSeparators: true,
                    floatingHeader: true,
                    order: GroupedListOrder.ASC,
                  );
                })
          ],
        ),
      ),
    );
  }
}

因此，如果我仍然没有意义，我将我的 hive 盒饭菜的值作为上述 MealModel 的实例。所以列表就像[MealModel 实例，MealModel 实例，...] 我只需要知道如何访问 MealModel 实例内部的值以传递给 GroupedList。

Answer 1

package:grouped_list图书馆正在使用 dynamic在他们的所有示例中，以简化没有泛型的人的使用。但在你的情况下这是一种误导，你正在失去强类型。
投到

return GroupedListView<MealModel, String>(

代替

return GroupedListView<dynamic, String>(

那么你所有的 element , meal和 item2变量将是 MealModel你可以做 element.mealName , 和 meal.calories按卡路里分组
对于排序问题，只需排序 mealList在将其传递给 GroupedListView 之前