Flutter/Dart: 使用 setState() 时更新一些变量但不更新其他变量

Question

我正在努力提高对 Flutter 的理解，但遇到了一个问题。我正在尝试创建一个应用程序来显示从列表中提取数据的卡片列表。底部有一个按钮，当用户单击它时会创建一张新卡片。

我正在尝试让每张卡片显示唯一的 'Round number'。因此，例如，每次用户单击该按钮时，都会添加一张卡片，在单词 'Round' 旁边显示序号。第一轮 > 第二轮 > 第三轮等等。

现在一切正常，除了每次按下按钮时，所有卡片都会更新为最新编号。因此，不是获取连续的卡片列表，而是将每张卡片更新为最新的轮数。

我做错了什么？谢谢。

这是我的代码：


import 'package:flutter/material.dart';

class Round {

  int roundNumber;
  int firstNumber;
  int secondNumber;

  Round({ this.roundNumber, this.firstNumber, this.secondNumber, });

}

int uid = 1;

List<Round> roundsList = [
  Round(roundNumber: uid, firstNumber: 1, secondNumber: 2),
];


class createLevels extends StatefulWidget {
  @override
  _createLevelsState createState() => _createLevelsState();
}

class _createLevelsState extends State<createLevels> {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        centerTitle: true,
          title: Text("Create Rounds",)
      ),
      body: Padding(
        padding: const EdgeInsets.fromLTRB(20, 20, 20.0, 20),
        child: Container(
          child: Column(
              children: <Widget>[
                Expanded(
                  child: ListView.builder(
                    itemCount: roundsList.length,
                      itemBuilder: (BuildContext context, int whatIsThisVariable) {
                      return roundCard(Round(roundNumber: uid, firstNumber: 2, secondNumber: 3,));
                      }
                  ),
                ),
                Text("$roundsList"),
                RaisedButton(
                  onPressed: () {
                    uid++;
                    roundsList.add(Round(roundNumber: uid));
                    setState(() {});
                  },
                    child: Text("Add Round"),
                ),
              ],
          ),
        ),
      ),
    );
  }
}

class roundCard extends StatelessWidget {

  final Round round;

  roundCard(this.round);

  // roundsList.add(Round(roundNumber: 1));

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Card(
          child: Padding(
            padding: const EdgeInsets.all(8.0),
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: <Widget>[
                Spacer(
                  flex: 1,
                ),
                Expanded(
                  child: Text('Round ${round.roundNumber}:'),
                  flex: 12,
                ),
                Expanded(
                  child: TextFormField(
                      textAlign: TextAlign.center,
                      decoration: InputDecoration(
                        hintText: '${round.firstNumber}',
                      ),
                  ),
                  flex: 3,
                ),
                Spacer(
                  flex: 1,
                ),
                Expanded(
                  child: TextFormField(
                      textAlign: TextAlign.center,
                      decoration: InputDecoration(
                        hintText: '${round.secondNumber}',
                      ),
                  ),
                  flex: 3,
                ),
              ],
            ),
          )
      ),
    );
  }
}

Answer 1

您可以复制粘贴运行下面的完整代码
您需要传递 index 而不是 uid
你可以调整你想要的第一个和第二个数字

代码片段

itemBuilder: (BuildContext context, int index) {
                  return roundCard(roundsList[index]);
                }),
...
onPressed: () {
                  uid++;
                  firstNumber++;
                  secondNumber++;
                  roundsList.add(
                      Round(roundNumber: uid, firstNumber: firstNumber, secondNumber: secondNumber));
                  setState(() {});
                }

工作演示

完整代码

import 'package:flutter/material.dart';

class Round {
  int roundNumber;
  int firstNumber;
  int secondNumber;

  Round({
    this.roundNumber,
    this.firstNumber,
    this.secondNumber,
  });
}

int uid = 1;
int firstNumber = 2;
int secondNumber = 3;

List<Round> roundsList = [
  Round(roundNumber: uid, firstNumber: 1, secondNumber: 2),
];

class createLevels extends StatefulWidget {
  @override
  _createLevelsState createState() => _createLevelsState();
}

class _createLevelsState extends State<createLevels> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
          centerTitle: true,
          title: Text(
            "Create Rounds",
          )),
      body: Padding(
        padding: const EdgeInsets.fromLTRB(20, 20, 20.0, 20),
        child: Container(
          child: Column(
            children: <Widget>[
              Expanded(
                child: ListView.builder(
                    itemCount: roundsList.length,
                    itemBuilder: (BuildContext context, int index) {
                      return roundCard(roundsList[index]);
                    }),
              ),
              Text("$roundsList"),
              RaisedButton(
                onPressed: () {
                  uid++;
                  firstNumber++;
                  secondNumber++;
                  roundsList.add(
                      Round(roundNumber: uid, firstNumber: firstNumber, secondNumber: secondNumber));
                  setState(() {});
                },
                child: Text("Add Round"),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

class roundCard extends StatelessWidget {
  final Round round;

  roundCard(this.round);

  // roundsList.add(Round(roundNumber: 1));

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Card(
          child: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: <Widget>[
            Spacer(
              flex: 1,
            ),
            Expanded(
              child: Text('Round ${round.roundNumber}:'),
              flex: 12,
            ),
            Expanded(
              child: TextFormField(
                textAlign: TextAlign.center,
                decoration: InputDecoration(
                  hintText: '${round.firstNumber}',
                ),
              ),
              flex: 3,
            ),
            Spacer(
              flex: 1,
            ),
            Expanded(
              child: TextFormField(
                textAlign: TextAlign.center,
                decoration: InputDecoration(
                  hintText: '${round.secondNumber}',
                ),
              ),
              flex: 3,
            ),
          ],
        ),
      )),
    );
  }
}

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: createLevels(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

Flutter/Dart: 使用 setState() 时更新一些变量但不更新其他变量

Flutter/Dart: update some variables but not others when using setState()

setstate

dart

flutter