问题

尝试使用按钮来排序整数值列表，当升序排列时，它可以工作，但再次按下“Sort Value”按钮返回原始状态时无法工作，卡住了。

import 'package:flutter/material.dart';

void main() {
  runApp(MaterialApp(home: MyApp()));
}

class Product {
  final String name;
  final String category;
  final int value;

  Product({
    required this.name,
    required this.category,
    required this.value,
  });
}

List<Product> productlist = [
  Product(name: 'Sandwich', category: 'Food', value: 2),
  Product(name: 'Fish', category: 'Food', value: 1),
  Product(name: 'Vegetable', category: 'Food', value: 9),
  Product(name: 'Meat', category: 'Food', value: 13),
  Product(name: 'Book', category: 'Item', value: 4),
  Product(name: 'Hammer', category: 'Item', value: 6),
  Product(name: 'Pen', category: 'Item', value: 5),
  Product(name: 'Car', category: 'Vehicle', value: 8),
  Product(name: 'Bike', category: 'Vehicle', value: 14),
  Product(name: 'Motor', category: 'Vehicle', value: 0),
  Product(name: 'Boat', category: 'Vehicle', value: 25),
];

class MyApp extends StatefulWidget {
  MyApp({Key? key}) : super(key: key);

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  final List<String> categories = ['Food', 'Item', 'Vehicle'];
  List<String> selectedCategories = [];
  bool isActive = true;

  @override
  Widget build(BuildContext context) {
    final filterProducts = productlist.where((product) {
      return selectedCategories.isEmpty ||
          selectedCategories.contains(product.category);
    }).toList();
    return Scaffold(
        appBar: AppBar(
          title: const Text("Filter Sorting"),
          centerTitle: true,
        ),
        body: Column(
          children: [
            Container(
                padding: const EdgeInsets.all(8),
                margin: const EdgeInsets.all(8),
                child: Row(
                  children: [
                    Expanded(
                        flex: 3,
                        child: Row(
                          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                          children: categories
                              .map((category) => FilterChip(
                                  selected:
                                      selectedCategories.contains(category),
                                  label: Text(category),
                                  onSelected: (selected) {
                                    setState(() {
                                      if (selected) {
                                        selectedCategories.add(category);
                                      } else {
                                        selectedCategories.remove(category);
                                      }
                                    });
                                  }))
                              .toList(),
                        )),
                    Expanded(
                      flex: 1,
                      child: ElevatedButton(
                          onPressed: () {
                            setState(() {
                              if (isActive) {
                                productlist
                                    .sort((b, a) => b.value.compareTo(a.value));
                              } else {
                                productlist.sort((a, b) =>
                                    a.value.compareTo(b.value));
                              }
                              isActive = !isActive;
                            });
                          },
                          child: const Text('Sort Value, \nLow to High',
                              style: TextStyle(fontSize: 10))),
                    ),
                  ],
                )),
            Expanded(
                child: ListView.builder(
                    itemCount: filterProducts.length,
                    itemBuilder: ((context, index) {
                      final product = filterProducts[index];
                      return Card(
                          elevation: 8,
                          margin: const EdgeInsets.all(8),
                          child: Container(
                            decoration: BoxDecoration(color: Colors.blue),
                            child: ListTile(
                                contentPadding: const EdgeInsets.symmetric(
                                    horizontal: 10, vertical: 10),
                                title: Text(
                                  product.name,
                                  style: const TextStyle(
                                      color: Colors.white,
                                      fontWeight: FontWeight.bold),
                                ),
                                subtitle: Text(
                                  '${product.value}',
                                  style: const TextStyle(
                                    color: Colors.white,
                                    fontWeight: FontWeight.bold,
                                  ),
                                )),
                          ));
                    })))
          ],
        ));
  }
}

我需要按升序排列顺序，然后还原整个列表，然后重复此操作。

英文:

Trying to use Button to sort the int value list, it works when ascending the order, but it doesn't work when going back to the original state by pressing the Sort Value button once more, stuck.

Initial Outcome

Outcome after Sort Value button pressed

import &#39;package:flutter/material.dart&#39;;
void main() {
runApp(MaterialApp(home: MyApp()));
}
class Product {
final String name;
final String category;
final int value;
Product({
required this.name,
required this.category,
required this.value,
});
}
List&lt;Product&gt; productlist = [
Product(name: &#39;Sandwich&#39;, category: &#39;Food&#39;, value: 2),
Product(name: &#39;Fish&#39;, category: &#39;Food&#39;, value: 1),
Product(name: &#39;Vegetable&#39;, category: &#39;Food&#39;, value: 9),
Product(name: &#39;Meat&#39;, category: &#39;Food&#39;, value: 13),
Product(name: &#39;Book&#39;, category: &#39;Item&#39;, value: 4),
Product(name: &#39;Hammer&#39;, category: &#39;Item&#39;, value: 6),
Product(name: &#39;Pen&#39;, category: &#39;Item&#39;, value: 5),
Product(name: &#39;Car&#39;, category: &#39;Vehicle&#39;, value: 8),
Product(name: &#39;Bike&#39;, category: &#39;Vehicle&#39;, value: 14),
Product(name: &#39;Motor&#39;, category: &#39;Vehicle&#39;, value: 0),
Product(name: &#39;Boat&#39;, category: &#39;Vehicle&#39;, value: 25),
];
class MyApp extends StatefulWidget {
MyApp({Key? key}) : super(key: key);
@override
State&lt;MyApp&gt; createState() =&gt; _MyAppState();
}
class _MyAppState extends State&lt;MyApp&gt; {
final List&lt;String&gt; categories = [&#39;Food&#39;, &#39;Item&#39;, &#39;Vehicle&#39;];
List&lt;String&gt; selectedCategories = [];
bool isActive = true;
@override
Widget build(BuildContext context) {
final filterProducts = productlist.where((product) {
return selectedCategories.isEmpty ||
selectedCategories.contains(product.category);
}).toList();
return Scaffold(
appBar: AppBar(
title: const Text(&quot;Fitler Sorting&quot;),
centerTitle: true,
),
body: Column(
children: [
Container(
padding: const EdgeInsets.all(8),
margin: const EdgeInsets.all(8),
child: Row(
children: [
Expanded(
flex: 3,
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: categories
.map((category) =&gt; FilterChip(
selected:
selectedCategories.contains(category),
label: Text(category),
onSelected: (selected) {
setState(() {
if (selected) {
selectedCategories.add(category);
} else {
selectedCategories.remove(category);
}
});
}))
.toList(),
)),
Expanded(
flex: 1,
child: ElevatedButton(
/** */
onPressed: () {
setState(() {
if (isActive) {
productlist
.sort((b, a) =&gt; b.value.compareTo(a.value));
} else {
productlist.toList();
}
});
},
child: const Text(&#39;Sort Value, \nLow to High&#39;,
style: TextStyle(fontSize: 10))),
),
],
)),
Expanded(
child: ListView.builder(
itemCount: filterProducts.length,
itemBuilder: ((context, index) {
final product = filterProducts[index];
return Card(
elevation: 8,
margin: const EdgeInsets.all(8),
child: Container(
decoration: BoxDecoration(color: Colors.blue),
child: ListTile(
contentPadding: const EdgeInsets.symmetric(
horizontal: 10, vertical: 10),
title: Text(
product.name,
style: const TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold),
),
subtitle: Text(
&#39;${product.value}&#39;,
style: const TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold,
),
)),
));
})))
],
));
}
}

I need to arrange the order ascendingly, then revert the whole list, rinse and repeat.

答案1

得分: 1

在列表首次创建或修改时，保存另一个变量的副本，例如

originalList = productlist.toList();

这样你的程序就变成了：

import 'package:flutter/material.dart';

void main() {
  runApp(MaterialApp(home: MyApp()));
}

class Product {
  final String name;
  final String category;
  final int value;

  Product({
    required this.name,
    required this.category,
    required this.value,
  });
}

List<Product> productlist = [
  Product(name: 'Sandwich', category: 'Food', value: 2),
  Product(name: 'Fish', category: 'Food', value: 1),
  Product(name: 'Vegetable', category: 'Food', value: 9),
  Product(name: 'Meat', category: 'Food', value: 13),
  Product(name: 'Book', category: 'Item', value: 4),
  Product(name: 'Hammer', category: 'Item', value: 6),
  Product(name: 'Pen', category: 'Item', value: 5),
  Product(name: 'Car', category: 'Vehicle', value: 8),
  Product(name: 'Bike', category: 'Vehicle', value: 14),
  Product(name: 'Motor', category: 'Vehicle', value: 0),
  Product(name: 'Boat', category: 'Vehicle', value: 25),
];

class MyApp extends StatefulWidget {
  MyApp({Key? key}) : super(key: key);

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  final List<String> categories = ['Food', 'Item', 'Vehicle'];
  List<String> selectedCategories = [];
  final originalList = productlist.toList();
  bool isActive = true;

  @override
  Widget build(BuildContext context) {
    final filterProducts = productlist.where((product) {
      return selectedCategories.isEmpty ||
          selectedCategories.contains(product.category);
    }).toList();
    return Scaffold(
        appBar: AppBar(
          title: const Text("Fitler Sorting"),
          centerTitle: true,
        ),
        body: Column(
          children: [
            Container(
                padding: const EdgeInsets.all(8),
                margin: const EdgeInsets.all(8),
                child: Row(
                  children: [
                    Expanded(
                        flex: 3,
                        child: Row(
                          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                          children: categories
                              .map((category) => FilterChip(
                                  selected: selectedCategories.contains(category),
                                  label: Text(category),
                                  onSelected: (selected) {
                                    setState(() {
                                      if (selected) {
                                        selectedCategories.add(category);
                                      } else {
                                        selectedCategories.remove(category);
                                      }
                                    });
                                  }))
                              .toList(),
                        )),
                    Expanded(
                      flex: 1,
                      child: ElevatedButton(
                        onPressed: () {
                          setState(() {
                            if (isActive) {
                              productlist.sort((b, a) =>
                                  b.value.compareTo(a.value));
                            } else {
                              productlist = originalList.toList();
                            }
                            isActive = !isActive;
                          });
                        },
                        child: const Text('Sort Value, \nLow to High',
                            style: TextStyle(fontSize: 10)),
                      ),
                    ),
                  ],
                )),
            Expanded(
                child: ListView.builder(
                    itemCount: filterProducts.length,
                    itemBuilder: ((context, index) {
                      final product = filterProducts[index];
                      return Card(
                          elevation: 8,
                          margin: const EdgeInsets.all(8),
                          child: Container(
                            decoration: BoxDecoration(color: Colors.blue),
                            child: ListTile(
                                contentPadding: const EdgeInsets.symmetric(
                                    horizontal: 10, vertical: 10),
                                title: Text(
                                  product.name,
                                  style: const TextStyle(
                                      color: Colors.white,
                                      fontWeight: FontWeight.bold),
                                ),
                                subtitle: Text(
                                  '${product.value}',
                                  style: const TextStyle(
                                    color: Colors.white,
                                    fontWeight: FontWeight.bold,
                                  ),
                                )),
                          ));
                    })))
          ],
        ));
  }
}

英文:

When the list is first created or modified save a copy of it in another variable, like for example

originalList = productlist.toList();

so your program becomes

import &#39;package:flutter/material.dart&#39;;
void main() {
runApp(MaterialApp(home: MyApp()));
}
class Product {
final String name;
final String category;
final int value;
Product({
required this.name,
required this.category,
required this.value,
});
}
List&lt;Product&gt; productlist = [
Product(name: &#39;Sandwich&#39;, category: &#39;Food&#39;, value: 2),
Product(name: &#39;Fish&#39;, category: &#39;Food&#39;, value: 1),
Product(name: &#39;Vegetable&#39;, category: &#39;Food&#39;, value: 9),
Product(name: &#39;Meat&#39;, category: &#39;Food&#39;, value: 13),
Product(name: &#39;Book&#39;, category: &#39;Item&#39;, value: 4),
Product(name: &#39;Hammer&#39;, category: &#39;Item&#39;, value: 6),
Product(name: &#39;Pen&#39;, category: &#39;Item&#39;, value: 5),
Product(name: &#39;Car&#39;, category: &#39;Vehicle&#39;, value: 8),
Product(name: &#39;Bike&#39;, category: &#39;Vehicle&#39;, value: 14),
Product(name: &#39;Motor&#39;, category: &#39;Vehicle&#39;, value: 0),
Product(name: &#39;Boat&#39;, category: &#39;Vehicle&#39;, value: 25),
];
class MyApp extends StatefulWidget {
MyApp({Key? key}) : super(key: key);
@override
State&lt;MyApp&gt; createState() =&gt; _MyAppState();
}
class _MyAppState extends State&lt;MyApp&gt; {
final List&lt;String&gt; categories = [&#39;Food&#39;, &#39;Item&#39;, &#39;Vehicle&#39;];
List&lt;String&gt; selectedCategories = [];
final originalList = productlist.toList();
bool isActive = true;
@override
Widget build(BuildContext context) {
final filterProducts = productlist.where((product) {
return selectedCategories.isEmpty ||
selectedCategories.contains(product.category);
}).toList();
return Scaffold(
appBar: AppBar(
title: const Text(&quot;Fitler Sorting&quot;),
centerTitle: true,
),
body: Column(
children: [
Container(
padding: const EdgeInsets.all(8),
margin: const EdgeInsets.all(8),
child: Row(
children: [
Expanded(
flex: 3,
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: categories
.map((category) =&gt; FilterChip(
selected:
selectedCategories.contains(category),
label: Text(category),
onSelected: (selected) {
setState(() {
if (selected) {
selectedCategories.add(category);
} else {
selectedCategories.remove(category);
}
});
}))
.toList(),
)),
Expanded(
flex: 1,
child: ElevatedButton(
/** */
onPressed: () {
setState(() {
if (isActive) {
productlist
.sort((b, a) =&gt; b.value.compareTo(a.value));
} else {
productlist = originalList.toList();
}
isActive = !isActive;
});
},
child: const Text(&#39;Sort Value, \nLow to High&#39;,
style: TextStyle(fontSize: 10))),
),
],
)),
Expanded(
child: ListView.builder(
itemCount: filterProducts.length,
itemBuilder: ((context, index) {
final product = filterProducts[index];
return Card(
elevation: 8,
margin: const EdgeInsets.all(8),
child: Container(
decoration: BoxDecoration(color: Colors.blue),
child: ListTile(
contentPadding: const EdgeInsets.symmetric(
horizontal: 10, vertical: 10),
title: Text(
product.name,
style: const TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold),
),
subtitle: Text(
&#39;${product.value}&#39;,
style: const TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold,
),
)),
));
})))
],
));
}
}
</details>

通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。

如何在Flutter中将列表恢复到开头？

问题

答案1

Flutter – 我如何在接收到UDP数据时中断？

“unassigned variable”错误如何修复，尽管变量已初始化？

AES加密和解密在Golang和Flutter之间的实现

“Flutter Text Isn’t Displaying” 可以翻译为 “Flutter 文本未显示”。

What's the correct way to type hint an empty list as a literal in python?

如何在Highcharts Gantt中更改本地化的星期名称

如何在同一个流中使用多个过滤器和映射函数？

如何使用Map/Set来将代码优化到O(n)？

.NET MAUI Android在GitHub Actions上构建失败，错误代码为1。

如何在Playwright视觉比较中屏蔽多个定位器？

在C++中，可以使用可变模板参数来检索类型的内部类型。

selenium.common.exceptions.StaleElementReferenceException: Message: stale element reference: stale element not found

Creating and opening a URL to log in to Website via Basic Auth with Robot Framework/Selenium (Python)

AG Grid 在上下文菜单中以大文本形式打开

发表评论