Flutter - 将来自不同文本字段的值相乘

Question

我需要你的帮助，

我想将来自不同文本字段的值相乘。我面临着 * 不能与 TexteditingController() 一起使用的问题:

void _calculation() {
    _volume = lenCon * widCon * higCon;
    print(_volume);
  }

我之前是否需要将 lenCon 之类的变量转换为 double？我怎样才能做到这一点？ var lenConInt = double.parse(lenCon); 不起作用。

RaisedButton 必须执行 _calculation 并用适当的值更改文本。我需要 StatlessWidget 还是 SetState？

提前致谢!

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

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

class _MyHomePageState extends State<MyHomePage> {
  var _volume = 0;

//  var _lenght;
//  var _width;
//  var _hight;

  void _calculation() {
    _volume = lenCon * widCon * higCon;
    print(_volume);
  }

  final lenCon = new TextEditingController();
  final widCon = new TextEditingController();
  final higCon = new TextEditingController();

  // var lenConInt = double.parse(lenCon);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Padding(
          padding: const EdgeInsets.all(10.0),
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              TextField(
                controller: lenCon,
                keyboardType: TextInputType.number,
                decoration: InputDecoration(
                  hintText: 'Länge',
                ),
              ),
              TextField(
                controller: widCon,
                keyboardType: TextInputType.number,
                decoration: InputDecoration(
                  hintText: 'Breite',
                ),
              ),
              TextField(
                controller: higCon,
                keyboardType: TextInputType.number,
                decoration: InputDecoration(
                  hintText: 'Höhe',
                ),
              ),
              RaisedButton(
                onPressed: (_calculation),
                child: Text('Berechnen'),
              ),
              Text('Your Volume is: $_volume'),
            ],
          ),
        ),
      ),
    );
  }
}

Answer 1

试试这个，让它发挥作用:

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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 _volume;

  @override
  initState(){
      _volume = 0;
  }

  void _calculation() {
    setState((){
        _volume = int.parse(lenCon.text) * int.parse(widCon.text) * int.parse(higCon.text);
        },
    );
    print(_volume);
  }

  final lenCon = TextEditingController();
  final widCon = TextEditingController();
  final higCon = TextEditingController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Padding(
          padding: const EdgeInsets.all(10.0),
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              TextField(
                controller: lenCon,
                keyboardType: TextInputType.number,
                decoration: InputDecoration(
                  hintText: 'Länge',
                ),
              ),
              TextField(
                controller: widCon,
                keyboardType: TextInputType.number,
                decoration: InputDecoration(
                  hintText: 'Breite',
                ),
              ),
              TextField(
                controller: higCon,
                keyboardType: TextInputType.number,
                decoration: InputDecoration(
                  hintText: 'Höhe',
                ),
              ),
              RaisedButton(
                onPressed: (_calculation),
                child: Text('Berechnen'),
              ),
              Text('Your Volume is: $_volume'),
            ],
          ),
        ),
      ),
    );
  }
}

首先，您需要在字符串和整数之间进行某种类型的转换(如果需要，甚至可以是 double )。其次，您应该将生成的 _volume 置于一个状态中，以便在您更新状态时(通过 setState)刷新 UI。尽量避免使用 var 并改用具体类型。从长远来看，它将对您有所帮助。