（颤振）列表视图构建器不会显示复选框列表

Question

它没有显示任何错误 但列表视图生成器不显示任何复选框列表。 我哪里出错了？ 请纠正我。

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';
import 'package:selfordering1/models/addon.dart';
import 'package:selfordering1/models/models.dart';

class Americano extends StatefulWidget {
  @override
  _AmericanoState createState() => _AmericanoState();
}

class _AmericanoState extends State<Americano> {
  List<Products> beverages = [];
  List<addonsize> listSize = [];
  List<addontopping> listTopping = [];
  var items = Products().beverages;

  bool _value = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(''),
        leading: IconButton(
          icon: Icon(Icons.arrow_back, color: Colors.white),
          onPressed: () {
            Navigator.pop(context);
          },
        ),
        backgroundColor: Colors.transparent,
        elevation: 0.0,
      ),
      extendBodyBehindAppBar: true,
      body: Container(
        decoration: BoxDecoration(
          image: DecorationImage(
            image: AssetImage('assets/lightwood.jpg'),
            fit: BoxFit.fill,
          ),
        ),
        child: ListView(
          physics: NeverScrollableScrollPhysics(),
          primary: false,
          padding: const EdgeInsets.all(100),
          children: <Widget>[
            Column(
              mainAxisAlignment: MainAxisAlignment.start,
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                Container(
                  width: 200,
                  height: 200,
                  decoration: BoxDecoration(
                    image: DecorationImage(
                      image: AssetImage(items[1].img),
                    ),
                  ),
                ),
                Text(
                  items[1].name,
                  style: TextStyle(
                      fontWeight: FontWeight.bold,
                      fontSize: 30,
                      color: Colors.brown),
                ),
                Container(
                  margin: EdgeInsets.all(50),
                  child: Text(
                    items[1].price.toStringAsFixed(0) + ' บาท',
                    style: TextStyle(
                        fontWeight: FontWeight.bold,
                        fontSize: 30,
                        color: Colors.brown),
                  ),
                ),
              ],
            ),
               Row(
                 children: [
                   Expanded(
                     child: ListView.builder(
                            shrinkWrap: true,
                            itemCount: listTopping.length,
                            itemBuilder: (BuildContext context, int i) {
                              return new Card(
                                child: new Container(
                                  padding: new EdgeInsets.all(10.0),
                                  child: Column(
                                    children: <Widget>[
                                      new CheckboxListTile(
                                        activeColor: Colors.blue,
                                        dense: true,
                                        //font change
                                        title: new Text(
                                          listTopping[i].topping,
                                          style: TextStyle(
                                              fontSize: 25,
                                              fontWeight: FontWeight.bold,
                                              ),
                                        ),
                                        value: listTopping[i].isCheck,
                                        secondary: Container(
                                          height: 50,
                                          width: 50,
                                          child: Text(listTopping[i]
                                              .price
                                              .toStringAsFixed(0)),
                                        ),
                                        onChanged: (bool? val) {
                                          itemChange(val!, i);
                                        },
                                      ),
                                    ],
                                  ),
                                ),
                              );
                            }),
                   ),
                 ],
               ),
                ],
            ),
      ),
    );
  }

  void itemChange(bool val, int i) {
    setState(() {
      listTopping[i].isCheck = val;
    });
  }
}

这是模型

import 'package:flutter/material.dart';

class addonsize {
  int id;
  String size;
  double price;

  addonsize({
    required this.id,
    required this.size,
    required this.price,
  });
}


List<addonsize> listSize = [
  addonsize(
    id: 6,
    size: 'Grande',
    price: 30,
  ),
  addonsize(
    id: 7,
    size: 'Venti',
    price: 50,
  ),
];


class addontopping {
  int id;
  String topping;
  double price;
  bool isCheck;

  addontopping({
    required this.id,
    required this.topping,
    required this.price,
    required this.isCheck,
  });
}

List<addontopping> listTopping = [
  addontopping(
    id: 8,
    topping: 'Whipcream',
    price: 0,
    isCheck: true,
  ),
  addontopping(
    id: 9,
    topping: 'Javachip',
    price: 30,
    isCheck: false,
  ),
  addontopping(
    id: 10,
    topping: 'SoyMilk',
    price: 20,
    isCheck: false,
  ),
  addontopping(
    id: 11,
    topping: 'ExtraSyrup',
    price: 30,
    isCheck: false,
  ),
];

如果有更详细的需要，请告诉我。 另外，如果不是太多，我希望价格根据顶部的点击进行相应调整。请给我看例子@_@

Answer 1

因为您的“CheckboxListTile”是由带有 listTopping 列表的“ListView.builder”构建的。
但在 '_AmericanoState' 类中，listTopping 为空。

...
List<addontopping> listTopping = [];
...

ListView.builder(
                            shrinkWrap: true,
                            itemCount: listTopping.length,
                            itemBuilder: (BuildContext context, int i) {
                              return new Card(
                                child: new Container(
                                  padding: new EdgeInsets.all(10.0),
                                  child: Column(
                                    children: <Widget>[
                                      new CheckboxListTile(

您需要更改 '_AmericanoState' 类中的 listTopping 变量，如下所示。

List<addontopping> listTopping = [
  addontopping(
    id: 8,
    topping: 'Whipcream',
    price: 0,
    isCheck: true,
  ),
  addontopping(
    id: 9,
    topping: 'Javachip',
    price: 30,
    isCheck: false,
  ),
  addontopping(
    id: 10,
    topping: 'SoyMilk',
    price: 20,
    isCheck: false,
  ),
  addontopping(
    id: 11,
    topping: 'ExtraSyrup',
    price: 30,
    isCheck: false,
  ),
];

Answer 2

原因是您在 2 个不同的文件中有 2 个 listTopping 和 2 个 listSize 变量。它将优先于您本地 _AmericanoState 类中的一个（没有数据），而不是另一个（有数据）。

要解决此问题，只需将_AmericanoState 中的listTopping 和listSize 替换为其他文件中包含数据的列表即可。

class Americano extends StatefulWidget {
  @override
  _AmericanoState createState() => _AmericanoState();
}

class _AmericanoState extends State<Americano> {
  List<Products> beverages = [];
  var items = Products().beverages;

  List<addonsize> listSize = [
  addonsize(
    id: 6,
    size: 'Grande',
    price: 30,
  ),
  addonsize(
    id: 7,
    size: 'Venti',
    price: 50,
    ),
  ];

  List<addontopping> listTopping = [
  addontopping(
    id: 8,
    topping: 'Whipcream',
    price: 0,
    isCheck: true,
  ),
  addontopping(
    id: 9,
    topping: 'Javachip',
    price: 30,
    isCheck: false,
  ),
  addontopping(
    id: 10,
    topping: 'SoyMilk',
    price: 20,
    isCheck: false,
  ),
  addontopping(
    id: 11,
    topping: 'ExtraSyrup',
    price: 30,
    isCheck: false,
    ),
  ];

对于每次选择浇头后的价格更新，您可以使用此方法。这会返回一个您可以在 UI 中使用的 double 值：

double calculatePrice() {
    if (listTopping.isNotEmpty) {
      var _price;
      // Get those toppings that are chosen (`isCheck` is true)
      final chosenTopping = listTopping.where((element) => element.isCheck);

      // Calculate the sum
      for (var item in chosenTopping) {
        _price += item.price;
      }
      return _price;
    }
    return 0.0;
  }

快速说明：您应该在 Flutter 中为每个类名使用 UpperCamelCase 作为一个好的做法（所以 AddonTopping 而不是 addontopping）。阅读更多关于styling here