全局变量或将变量的值传递到另一个屏幕

huangapple
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英文:

Global variable or passing the value of a variable to another screen

问题

我明白你的问题。你想要将在 "MyHomePage" 类中的 "bal" 变量的值传递到 "PageResult" 类中。以下是两种可能的解决方案：

解决方案1：通过构造函数传递数据

在 "PageResult" 类中创建一个构造函数，用于接收 "bal" 变量的值。然后，在 "MyHomePage" 类中创建 "PageResult" 类的实例时，将 "bal" 的值传递给构造函数。这是一个示例：

在 "PageResult" 类中：

  1. class PageResult extends StatefulWidget {
  2.   final int bal; // 在构造函数中接收bal的值
  4.   PageResult(this.bal);
  6.   @override
  7.   MyWidgetState createState() => MyWidgetState();
  8. }
  10. class MyWidgetState extends State<PageResult> {
  11.   @override
  12.   Widget build(BuildContext context) {
  13.     return Scaffold(
  14.       appBar: AppBar(
  15.         title: Text("Test Result"),
  16.       ),
  17.       body: Text('bal的值: ${widget.bal}'), // 使用widget.bal来访问bal的值
  18.     );
  19.   }
  20. }

在 "MyHomePage" 类中：

  1. ElevatedButton(
  2.   onPressed: () {
  3.     QuestionsList.shared.nextQuestion();
  4.     // 其他代码...
  5.     Navigator.push(
  6.       context,
  7.       MaterialPageRoute(
  8.         builder: (context) => PageResult(bal), // 通过构造函数传递bal的值
  9.       ),
  10.     );
  11.   },
  12.   child: Text('NEXT'),
  13. );

解决方案2：使用全局变量

你也可以使用全局变量来存储 "bal" 的值，以便在不同类之间共享。在Dart中，你可以使用全局变量或全局状态管理库来实现这一点，例如Provider、GetX等。这里提供一个全局变量的示例：

在一个单独的Dart文件（例如globals.dart）中创建一个全局变量：

  1. int bal = 0;

然后，在 "MyHomePage" 类和 "PageResult" 类中都导入这个Dart文件，就可以访问和更新全局变量 "bal"。

请注意： 使用全局变量需要小心，因为它们可能会导致代码的维护性和可读性下降。最好的做法是使用状态管理库来处理应用程序的状态，以便更好地组织和维护代码。

英文:

I guess that the question is stupid, but for a day I can not solve this simplest problem.

In the class "MyHomePage" I have a variable "bal" which counts the correct answers.

  1. import &#39;package:australia/qlist.dart&#39;;
  2. import &#39;package:flutter/material.dart&#39;;
  4. class MyHomePage extends StatefulWidget {
  5.   const MyHomePage({Key? key}) : super(key: key);
  6.   @override
  7.   State&lt;MyHomePage&gt; createState() =&gt; _MyHomePageState();
  8. }
  10. class _MyHomePageState extends State&lt;MyHomePage&gt; {
  11.   int _counter = 1;
  12.   int bal = 0;
  13.   int bad = 0;
  17.   List&lt;Color&gt; colorsList = [
  18.     Colors.white,
  19.     Colors.white,
  20.     Colors.white,
  21.     Colors.white
  22.   ];
  25.   List&lt;String&gt; answers = [];
  26.   @override
  27.   void initState() {
  28.     answers.addAll([
  29.       QuestionsList.shared.getCurrentQuestion().correctAnswer,
  30.       QuestionsList.shared.getCurrentQuestion().dis1,
  31.       QuestionsList.shared.getCurrentQuestion().dis2,
  32.       QuestionsList.shared.getCurrentQuestion().dis3,
  33.     ]);
  34.     answers.shuffle();
  35.   }
  39.   @override
  40.   Widget build(BuildContext context) {
  41.     return Scaffold(
  42.         appBar: AppBar(
  43.           title: Text (&quot;Exam test&quot;),
  44.         ),
  45.         body: Column(
  46.             mainAxisAlignment: MainAxisAlignment.spaceBetween,
  47.             children: [
  50.               Column(
  51.                 children: [
  52.                   Padding(
  53.                     padding: const EdgeInsets.all(8.0),
  54.                     child: Row(
  55.                       children: [
  56.                         Text(&#39;$_counter&#39;), Text(&#39;/20____&#39;), Text(&#39;$bal&#39;), Text(&#39;____&#39;), Text(&#39;$bad&#39;),
  57.                       ],
  58.                     ),
  59.                   ),
  61.                   Center(
  62.                       child: Text(QuestionsList.shared.getCurrentQuestion().question)),
  63.                 ],
  64.               ),
  67.               Column(
  68.                 children: [
  69.                   Container(
  70.                     width: double.infinity,
  71.                     child: Card(
  72.                       color: colorsList[0],
  73.                       child: InkWell(
  74.                         child: Container(
  75.                             margin: const EdgeInsets.all(5.0),
  76.                             child: Text(answers[0])),
  77.                         onTap: () {
  78.                           if (answers[0] ==
  79.                               QuestionsList.shared.getCurrentQuestion().correctAnswer) {
  80.                             colorsList[0] = Colors.green;
  81.                             setState(() {
  82.                               if (bad==0) {bal++;}
  83.                               ;
  84.                             });
  85.                           } else {
  86.                             colorsList[0] = Colors.red;
  87.                             setState(() {bad++;});
  88.                           }
  89.                         },
  90.                       ),
  91.                     ),),
  92.                   Container(
  93.                     width: double.infinity,
  94.                     child: Card(
  95.                       color: colorsList[1],
  96.                       child: InkWell(
  97.                         child: Container(
  98.                             margin: const EdgeInsets.all(5.0),
  99.                             child: Text(answers[1])),
  100.                         onTap: () {
  101.                           if (answers[1] ==
  102.                               QuestionsList.shared.getCurrentQuestion().correctAnswer) {
  103.                             colorsList[1] = Colors.green;
  104.                             setState(() {
  105.                               if (bad==0) {bal++;};
  106.                             });
  107.                           } else {
  108.                             colorsList[1] = Colors.red;
  109.                             setState(() {bad++;});
  110.                           }
  111.                         },
  112.                       ),
  113.                     ),),
  114.                   Container(
  115.                     width: double.infinity,
  116.                     child: Card(
  117.                       color: colorsList[2],
  118.                       child: InkWell(
  119.                         child: Container(
  120.                             margin: const EdgeInsets.all(5.0),
  121.                             child: Text(answers[2])),
  122.                         onTap: () {
  123.                           if (answers[2] ==
  124.                               QuestionsList.shared.getCurrentQuestion().correctAnswer) {
  125.                             colorsList[2] = Colors.green;
  126.                             setState(() {
  127.                               if (bad==0) {bal++;};
  128.                             });
  129.                           } else {
  130.                             colorsList[2] = Colors.red;
  131.                             setState(() {bad++;});
  132.                           }
  133.                         },
  134.                       ),
  135.                     ),),
  136.                   Container(
  137.                     width: double.infinity,
  138.                     child: Card(
  139.                       color: colorsList[3],
  140.                       child: InkWell(
  141.                         child: Container(
  142.                             margin: const EdgeInsets.all(5.0),
  143.                             child: Text(answers[3])),
  144.                         onTap: () {
  145.                           if (answers[3] ==
  146.                               QuestionsList.shared.getCurrentQuestion().correctAnswer) {
  147.                             colorsList[3] = Colors.green;
  148.                             setState(() {
  149.                               if (bad==0) {bal++;};
  150.                             });
  151.                           } else {
  152.                             colorsList[3] = Colors.red;
  153.                             setState(() {bad++;});
  154.                           }
  155.                         },
  156.                       ),
  157.                     ),),
  161.                   ElevatedButton(
  162.                       onPressed: () {
  163.                         QuestionsList.shared.nextQuestion();
  164.                         colorsList[0] = Colors.white;
  165.                         colorsList[1] = Colors.white;
  166.                         colorsList[2] = Colors.white;
  167.                         colorsList[3] = Colors.white;
  168.                         answers.clear();
  169.                         answers.addAll([
  170.                           QuestionsList.shared.getCurrentQuestion().correctAnswer,
  171.                           QuestionsList.shared.getCurrentQuestion().dis1,
  172.                           QuestionsList.shared.getCurrentQuestion().dis2,
  173.                           QuestionsList.shared.getCurrentQuestion().dis3,
  174.                         ]);
  175.                         answers.shuffle();
  176.                         setState(() {
  177.                           _counter++; bad=0;
  178.                           if (_counter==20) {Navigator.push(
  179.                             context,
  180.                             MaterialPageRoute(
  181.                               builder: (context)
  182.                                 =&gt; PageResult()
  184.                             ),
  185.                           );}
  186.                         });
  187.                       },
  188.                       child: Text(&#39;NEXT&#39;)),
  189.                   ElevatedButton(
  190.                       onPressed: () {
  191.                         Navigator.pop(context);
  192.                       },
  193.                       child: Text(&#39;BACK&#39;)),
  196.                 ],
  197.               )
  198.             ]));
  199.   }
  200. }

And I need to transfer its value to the "PageResult" class.

  1. class PageResult extends StatefulWidget {
  2.   
  3.   createState() =&gt; new MyWidgetState();
  4. }
  5. class MyWidgetState extends State&lt;PageResult&gt; {
  8.   Widget build(BuildContext context) {
  9.     return Scaffold(
  10.         appBar: AppBar(
  11.             title: Text (&quot;Test Result&quot;)
  12.     ),
  13. // body: Text(&#39;$bal&#39;),
  17.     );
  18.   }
  19. }

I understand that there are 2 solutions.

1. Pass data from class to class

2. Make the "bal" variable global.

But I can't find a solution in the manuals. Help please.

答案1

得分: 1

你可以通过PageResult小部件的参数化构造函数传递变量，并从State中使用引用widget.bal。

  1. class PageResult extends StatefulWidget {
  2.   PageResult({required this.bal}) : super();
  3.   final int bal;
  5.   createState() => new MyWidgetState();
  6. }
  8. class MyWidgetState extends State<PageResult> {
  9.   Widget build(BuildContext context) {
  10.     return Scaffold(
  11.       appBar: AppBar(
  12.         title: Text("Test Result")
  13.       ),
  14.       body: Center(
  15.         child: Text('${widget.bal}'),
  16.       )
  17.     );
  18.   }
  19. }

在推送路由时使用：

  1. Navigator.push(
  2.   context,
  3.   MaterialPageRoute(
  4.     builder: (context) => PageResult(bal: bal)
  5.   )
  6. );
英文:

You can pass the variable with a parameterised constructor of PageResult widget. And use with the reference widget.bal from State

  1. class PageResult extends StatefulWidget {
  2.   PageResult({required this.bal}) : super() ;
  3.   final int bal;  
  5.   createState() =&gt; new MyWidgetState();
  6. }
  7. class MyWidgetState extends State&lt;PageResult&gt; {
  10.   Widget build(BuildContext context) {
  11.     return Scaffold(
  12.         appBar: AppBar(
  13.             title: Text (&quot;Test Result&quot;)
  14.     ),
  15. body: Center(
  16.         child: Text(&#39;${widget.bal}&#39;),
  17.       )
  18.     );
  19.   }
  20. }

And while pushing the route

  1.              Navigator.push(
  2.                             context,
  3.                             MaterialPageRoute(
  4.                               builder: (context)
  5.                                 =&gt; PageResult(bal: bal)
  7.                             ),
  8.                           );

huangapple
  • 本文由 发表于 2023年2月24日 15:28:38
  • 转载请务必保留本文链接：https://go.coder-hub.com/75553663.html
  • dart
  • flutter
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