如何修复错误“每个 child 必须恰好布置一次。”在颤抖中

Question

卡的颜色改变了一次，但随后错误一直出现在调试控制台中，并且与应用程序的连接丢失。

它说相关的 error-causing 小部件是脚手架。这个错误也在终端

断言失败：第 4978 行第 16 行：'child is! ParentDataElement<ParentData>'：不正确。

main.dart

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

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

class BMICalculator extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(
        scaffoldBackgroundColor: Color(0xFF090C22),
        colorScheme: ColorScheme.fromSwatch().copyWith(
          primary: Color(0xFF090C22),
        ),
      ),
      home: InputPage(),
    );
  }
}

input_page.dart

import 'package:flutter/material.dart';
import 'package:font_awesome_flutter/font_awesome_flutter.dart';
import 'icon_content.dart';
import 'reusable_card.dart';

const bottomContainerHeight = 80.0;
const activeCardColor = Color(0xFF1D1E33);
const inactiveCardColor = Color(0xFF111328);
const bottomContainerColor = Color(0xFFEB1555);

class InputPage extends StatefulWidget {
  @override
  _InputPageState createState() => _InputPageState();
}

class _InputPageState extends State<InputPage> {
  Color maleCardColor = inactiveCardColor;
  Color femaleCardColor = inactiveCardColor;
  void updateColor(int gender) {
    if (gender == 1) {
      if (maleCardColor == inactiveCardColor) {
        maleCardColor = activeCardColor;
      } else {
        maleCardColor = inactiveCardColor;
      }
    }
    if (gender == 2) {
      if (femaleCardColor == inactiveCardColor) {
        femaleCardColor = activeCardColor;
      } else {
        femaleCardColor = inactiveCardColor;
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('BMI CALCULATOR'),
        centerTitle: true,
      ),
      body: Column(
        children: [
          Expanded(
            child: Row(
              children: [
                Expanded(
                  child: GestureDetector(
                    onTap: () {
                      setState(() {
                        print('Male');
                        updateColor(1);
                      });
                    },
                    child: ReusableCard(
                      colour: maleCardColor,
                      cardChild: IconContent(
                        label: 'MALE',
                        cardIcon: FontAwesomeIcons.mars,
                      ),
                    ),
                  ),
                ),
                Expanded(
                  child: GestureDetector(
                    onTap: () {
                      setState(() {
                        print('Female');
                        updateColor(2);
                      });
                    },
                    child: ReusableCard(
                      colour: femaleCardColor,
                      cardChild: IconContent(
                        label: 'FEMALE',
                        cardIcon: FontAwesomeIcons.venus,
                      ),
                    ),
                  ),
                ),
              ],
            ),
          ),
          Expanded(
            child: Expanded(
              child: ReusableCard(
                colour: activeCardColor,
              ),
            ),
          ),
          Expanded(
            child: Row(
              children: [
                Expanded(
                  child: ReusableCard(
                    colour: activeCardColor,
                  ),
                ),
                Expanded(
                  child: ReusableCard(
                    colour: activeCardColor,
                  ),
                ),
              ],
            ),
          ),
          Container(
            color: bottomContainerColor,
            margin: EdgeInsets.only(top: 10.0),
            width: double.infinity,
            height: bottomContainerHeight,
          )
        ],
      ),
    );
  }
}

reusable_card.dart

import 'package:flutter/material.dart';

class ReusableCard extends StatelessWidget {
  ReusableCard({@required this.colour, this.cardChild});

  final Color colour;
  final Widget cardChild;

  @override
  Widget build(BuildContext context) {
    return Container(
      child: cardChild,
      margin: EdgeInsets.all(15.0),
      decoration: BoxDecoration(
        borderRadius: BorderRadius.circular(10.0),
        color: colour,
      ),
    );
  }
}

icon_content.dart

import 'package:flutter/material.dart';

const labelTextStyle = TextStyle(
  fontSize: 18.0,
  color: Color(0xFF8D8E98),
);

class IconContent extends StatelessWidget {
  IconContent({this.cardIcon, this.label});

  final IconData cardIcon;
  final String label;

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Icon(cardIcon, size: 80.0),
        SizedBox(
          height: 15.0,
        ),
        Text(label, style: labelTextStyle)
      ],
    );
  }
}

我已经尝试了我所知道的一切，但似乎无法解决问题。

Answer 1

这里是问题的解决方案，有一个 Expanded 是其他 Expanded 的子项：

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('BMI CALCULATOR'),
        centerTitle: true,
      ),
      body: Column(
        children: [
          Expanded(
            child: Row(
              children: [
                Expanded(
                  child: GestureDetector(
                    onTap: () {
                      setState(() {
                        print('Male');
                        updateColor(1);
                      });
                    },
                    child: ReusableCard(
                      colour: maleCardColor,
                      cardChild: IconContent(
                        label: 'MALE',
                        cardIcon: FontAwesomeIcons.mars,
                      ),
                    ),
                  ),
                ),
                Expanded(
                  child: GestureDetector(
                    onTap: () {
                      setState(() {
                        print('Female');
                        updateColor(2);
                      });
                    },
                    child: ReusableCard(
                      colour: femaleCardColor,
                      cardChild: IconContent(
                        label: 'FEMALE',
                        cardIcon: FontAwesomeIcons.venus,
                      ),
                    ),
                  ),
                ),
              ],
            ),
          ),
          Expanded(              // <----- just remove the Expanded that was a parent of this one
            child: ReusableCard(
              colour: activeCardColor,
            ),
          ),
          Expanded(
            child: Row(
              children: [
                Expanded(
                  child: ReusableCard(
                    colour: activeCardColor,
                  ),
                ),
                Expanded(
                  child: ReusableCard(
                    colour: activeCardColor,
                  ),
                ),
              ],
            ),
          ),
          Container(
            color: bottomContainerColor,
            margin: EdgeInsets.only(top: 10.0),
            width: double.infinity,
            height: bottomContainerHeight,
          )
        ],
      ),
    );
  }

如何修复错误“每个 child 必须恰好布置一次。”在颤抖中

How to fix the error, " Each child must be laid out exactly once." in flutter

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