Question

因为函数有 bool 语句，我在这里使用了 Function(bool?)

Widget buildSwitchtile(String title, String desc, bool currentvalue,
          Function(bool?) updatevalue) {
        return SwitchListTile(
          title: Text(title),
          value: currentvalue,
          subtitle: Text(desc),
          onChanged: updatevalue,
        );
      }

出现以下错误如何解决？ 'bool?' 类型的值不能分配给“bool”类型的变量。请帮我解决这个问题。------------------------------------------- -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- --

import 'package:dishes_app/widgets/main_drawer.dart';
import 'package:flutter/material.dart';

class FilterScreen extends StatefulWidget {
  static const routeName = '/filters';

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

class _FilterScreenState extends State<FilterScreen> {
  bool _glutenFree = false;
  bool _vegetarian = false;
  bool _vegan = false;
  bool _lactoseFree = false;

  Widget buildSwitchtile(String title, String desc, bool currentvalue,
      Function(bool?) updatevalue) {
    return SwitchListTile(
      title: Text(title),
      value: currentvalue,
      subtitle: Text(desc),
      onChanged: updatevalue,
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Settings'),
      ),
      drawer: MainDrawer(),
      body: Column(
        children: [
          Container(
            padding: EdgeInsets.all(20.0),
            child: Text(
              'Adjust Your meal selection',
              style: Theme.of(context).textTheme.title,
            ),
          ),
          Expanded(
            child: ListView(
              children: [
                buildSwitchtile('Gluten-Free', 'Only include gluten-free meals',
                    _glutenFree, (newvalue) {
                  setState(() {
                    _glutenFree = newvalue;
                  });
                }),
                buildSwitchtile(
                    'Lactose-Free', 'Only include Lactose Free', _lactoseFree,
                    (newvalue) {
                  setState(() {
                    _lactoseFree = newvalue;
                  });
                }),
                buildSwitchtile('Vegetarian ', 'Only include Vegetarian food  ',
                    _vegetarian, (newvalue) {
                  setState(() {
                    _vegetarian = newvalue;
                  });
                }),
                buildSwitchtile('Vegan', 'Only include Vegan', _vegan,
                    (newvalue) {
                  setState(() {
                    _vegan = newvalue;
                  });
                })
              ],
            ),
          ),
        ],
      ),
    );
  }
}

Answer 1

输入“！”最后在使用那个 bool 时。 It(bool?myBool) 有一个可以为 null 的值，所以在使用它时，你必须做 myBool！

快速指南 https://youtu.be/Q_WloMNKOkU

Answer 2

onChanged 方法只能发出 bool。所以这样做。传递一个采用 bool 的方法。那么你不应该有你遇到的问题。

  Widget buildSwitchtile(String title, String desc, bool currentvalue,
      Function(bool) updatevalue) {
    return SwitchListTile(
      title: Text(title),
      value: currentvalue,
      subtitle: Text(desc),
      onChanged: updatevalue,
    );
  }

'bool?' 类型的值不能分配给“bool”类型的变量

2 个答案: