function - floatingactionbutton 不会调用刷新

Question

我正在制作一个简单的数学应用程序(请参阅下面的代码)。我现在的问题是为什么我的 float 操作按钮(刷新)不起作用。我已将刷新设置为 changeData，我正在尝试使用我的 widget.refresh 调用该函数。 (最后一行代码)。

稍后我也会尝试实现一些控制:)

一个完全不同的问题，但仍然是关于 flutter 的:关于在一个类中有多少行是可以的？有没有“嘿伙计，这太过分了”？

import 'package:flutter/material.dart';
import 'dart:math';

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

class MyHome extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'simple math',
      theme: ThemeData(primarySwatch: Colors.red),
      home: FirstClass(),
    );
  }
}

class FirstClass extends StatefulWidget {
  @override
  _FirstClassState createState() => _FirstClassState();
}

class _FirstClassState extends State<FirstClass> {
  final random = Random();
  int a, b, sum;
  String output;

  void changeData(String buttonName) {
    setState(() {
      a = random.nextInt(10);
      b = random.nextInt(10);

      if (buttonName == '+') {
        sum = a + b;
        output = '$a + $b = ';
      } else if (buttonName == '-') {
        if (a >= b) {
          sum = a - b;
          output = '$a - $b = ';
        } else if (b > a) {
          //sum cannot be negative here
          sum = b - a;
          output = '$b - $a = ';
        }
      }
      print(sum.toString());
      Navigator.of(context).popUntil(ModalRoute.withName('/'));
      Navigator.of(context).push(MaterialPageRoute(
          builder: (context) => SecondClass(
                sum: sum,
                refresh: changeData,
                output: output,
              )));
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('First Screen'),
      ),
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: <Widget>[
            RaisedButton(child: Text('+'), onPressed: () => 
         changeData('+')),
            RaisedButton(child: Text('-'), onPressed: () => changeData('- 
   ')),
              ],
            ),
          ),
        );
      }
    }

class SecondClass extends StatefulWidget {
  final int sum;
  final String output;

  final Function refresh;

  SecondClass({this.sum, this.refresh, this.output});

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

class _SecondClassState extends State<SecondClass> {
  String enterAnswer;
  String output = "";

  @override
  void initState() {
    super.initState();
  }

  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Second Screen'),
      ),
      body: Center(
        child: Container(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Text(widget.output),
                  Container(
                      width: 50.0,
                      child: TextField(
                        keyboardType: TextInputType.number,
                        onChanged: (val) {
                          enterAnswer = val;
                        },
                      )),
                ],
              ),
              RaisedButton(
                onPressed: () {
                  if (enterAnswer.isNotEmpty) {
                    if (enterAnswer == widget.sum.toString()) {
                      setState(() {
                        output = 'Correct!';
                      });
                    } else {
                      setState(() {
                        output = 'Sorry, Worong answer';
                      });
                     }
                  } else {
                    setState(() {
                       output = 'You must enter a value';
                    });
                  }
                },
                child: Text('Check Answer'),
              ),
              Text(output),
              FloatingActionButton(
                  child: Icon(Icons.refresh),
                  onPressed: () {
                    widget.refresh();
                  })
            ],
          ),
        ),
      ),
    );
  }
}

Answer 1

在您的代码中，您需要将参数传递为 -void changeData(String buttonName) 将字符串作为参数。

工作代码:

FloatingActionButton(
                  child: Icon(Icons.refresh),
                  onPressed: () {
                    widget.refresh('+');
                  })

更新:正确的方法是同时传递 Button Name 字符串。

import 'package:flutter/material.dart';
import 'dart:math';

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

class MyHome extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'simple math',
      theme: ThemeData(primarySwatch: Colors.red),
      home: FirstClass(),
    );
  }
}

class FirstClass extends StatefulWidget {
  @override
  _FirstClassState createState() => _FirstClassState();
}

class _FirstClassState extends State<FirstClass> {
  final random = Random();
  int a, b, sum;
  String output;

  void changeData(String buttonName) {
    setState(() {
      a = random.nextInt(10);
      b = random.nextInt(10);

      if (buttonName == '+') {
        sum = a + b;
        output = '$a + $b = ';
      } else if (buttonName == '-') {
        if (a >= b) {
          sum = a - b;
          output = '$a - $b = ';
        } else if (b > a) {
          //sum cannot be negative here
          sum = b - a;
          output = '$b - $a = ';
        }
      }
      print(sum.toString());
      Navigator.of(context).popUntil(ModalRoute.withName('/'));
      Navigator.of(context).push(MaterialPageRoute(
          builder: (context) => SecondClass(
                sum: sum,
                refresh: changeData,
                output: output,
                buttonName: buttonName,
              )));
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('First Screen'),
      ),
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: <Widget>[
            RaisedButton(child: Text('+'), onPressed: () => changeData('+')),
            RaisedButton(child: Text('-'), onPressed: () => changeData('-')),
          ],
        ),
      ),
    );
  }
}

class SecondClass extends StatefulWidget {
  final int sum;
  final String output;
  final String buttonName;

  final Function refresh;

  SecondClass({this.sum, this.refresh, this.output, this.buttonName});

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

class _SecondClassState extends State<SecondClass> {
  String enterAnswer;
  String output = "";

  @override
  void initState() {
    super.initState();
  }

  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Second Screen'),
      ),
      body: Center(
        child: Container(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Text(widget.output),
                  Container(
                      width: 50.0,
                      child: TextField(
                        keyboardType: TextInputType.number,
                        onChanged: (val) {
                          enterAnswer = val;
                        },
                      )),
                ],
              ),
              RaisedButton(
                onPressed: () {
                  if (enterAnswer.isNotEmpty) {
                    if (enterAnswer == widget.sum.toString()) {
                      setState(() {
                        output = 'Correct!';
                      });
                    } else {
                      setState(() {
                        output = 'Sorry, Worong answer';
                      });
                    }
                  } else {
                    setState(() {
                      output = 'You must enter a value';
                    });
                  }
                },
                child: Text('Check Answer'),
              ),
              Text(output),
              FloatingActionButton(
                  child: Icon(Icons.refresh),
                  onPressed: () {
                    widget.refresh(widget.buttonName);
                  })
            ],
          ),
        ),
      ),
    );
  }
}