Flutter：计算不同文本字段的几个值的问题

Question

我需要帮助解决问题。 我正在尝试检索一个值，该值是添加多个文本字段值的结果，以便能够在另一个屏幕中使用它（通过 sharedpreferencies 或 sqlite）......我似乎无法得到这个值（在我的示例中为“总值”）。 谁有我的方法？

import 'package:flutter/material.dart';

class Screen1 extends StatefulWidget {
  Screen1({Key key, this.title}) : super(key: key);
  final String title;
  @override
  _Screen1State createState() => _Screen1State();
}

class _Screen1State extends State<Screen1> {

  final myController1 = TextEditingController();
  final myController2 = TextEditingController();


  @override
  void dispose() {
    myController1.dispose();
    myController2.dispose();
    super.dispose();
  }
  double value1;
  double value2;
  //double totalvalues = value1 + value2;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Screen 1'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            Row(
              children: [
                Expanded(
                  child: TextField(
                    controller: myController1,
                    keyboardType: TextInputType.number,
                    onChanged: (val) {
                      setState(() {
                        value1 = double.parse(myController1.text) * 10;
                      });
                    },
                    decoration: InputDecoration(
                        hintText: '0'
                    ),
                  ),
                ),
                Expanded(
                    child: Center(
                        child: value1 != null
                            ? Text(value1.toStringAsFixed(0))
                            : Text('0')
                    )
                ),
              ],
            ),
            Row(
              children: [
                Expanded(
                  child: TextField(
                    controller: myController2,
                    keyboardType: TextInputType.number,
                    onChanged: (val) {
                      setState(() {
                        value2 = double.parse(myController2.text) * 5;
                      });
                    },
                    decoration: InputDecoration(
                        hintText: '0'
                    ),
                  ),
                ),
                Expanded(
                    child: Center(
                        child: value2 != null
                            ? Text(value2.toStringAsFixed(0))
                            : Text('0')
                    )
                ),
              ],
            ),
            Center(
              child: Text('totalvalues = value1 + value2'),
            ),
            Center(
                child: ElevatedButton(
                    onPressed: () {
                      print('$value1');
                      print('$value2');
                      myController1.clear();
                      myController2.clear();

                    },
                    child: Text('Next screen >')
                )
            )
          ],
        ),
      ),
    );
  }
}

Answer 1

这里的问题是你必须在每次值改变时重新计算totalvalue。

先声明变量而不初始化：

double totalvalues;

其次，在每个onChanged函数上，重新计算值：

对于value1：

onChanged: (val) {
    setState(() {
        value1 = double.parse(myController1.text) * 10;
        totalvalues = value1 + value2;
    });
},

对于value2：

onChanged: (val) {
    setState(() {
        value2 = double.parse(myController2.text) * 10;
        totalvalues = value1 + value2;
    });
},

然后，您将在每次更改输入时更新总价值并将其显示在您的文本中，如下所示：

Text('$value1 + $value2 = $totalvalues')

如果您希望有两个以上的值，或者totalvalue 的计算方式可以改变，我建议您将重新计算转移到一个函数中。

Answer 2

对于你的情况，你甚至不TextEditingController

class _Screen1State extends State<Screen1> {

 // final myController1 = TextEditingController();
 // final myController2 = TextEditingController();


  @override
  void dispose() {
   // myController1.dispose();
   // myController2.dispose();
    super.dispose();
  }
  double value1;
  double value2;
  //double totalvalues = value1 + value2;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Screen 1'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            Row(
              children: [
                Expanded(
                  child: TextField(
                    // controller: myController1,
                    keyboardType: TextInputType.number,
                    onChanged: (val) {
                      setState(() {
                        //value1 = double.parse(myController1.text) * 10;
                        value1 = double.parse(val) * 10;
                      });
                    },
                    decoration: InputDecoration(
                        hintText: '0'
                    ),
                  ),
                ),
                Expanded(
                    child: Center(
                        child: value1 != null
                            ? Text(value1.toStringAsFixed(0))
                            : Text('0')
                    )
                ),
              ],
            ),
            Row(
              children: [
                Expanded(
                  child: TextField(
                    // controller: myController2,
                    keyboardType: TextInputType.number,
                    onChanged: (val) {
                      setState(() {
                        // value2 = double.parse(myController2.text) * 5;
                        value2 = double.parse(val) * 5;

                      });
                    },
                    decoration: InputDecoration(
                        hintText: '0'
                    ),
                  ),
                ),
                Expanded(
                    child: Center(
                        child: value2 != null
                            ? Text(value2.toStringAsFixed(0))
                            : Text('0')
                    )
                ),
              ],
            ),
            Center(
              child: Text('totalvalues = ${value1 + value2}'),
            ),
            Center(
                child: ElevatedButton(
                    onPressed: () {
                      print('$value1');
                      print('$value2');
                      // myController1.clear();
                      // myController2.clear();
                      value1=0;
                      value2=0;
                    },
                    child: Text('Next screen >')
                )
            )
          ],
        ),
      ),
    );
  }
}