flutter - 如果我习惯用 Switch 小部件上的新 val 更改状态，如何使用函数回调？

Question

我尝试使用 Switch 小部件更改新状态但无法使用，以防万一我创建动态函数并将用于小部件树，在函数中我在 Switch 小部件的参数处发送回调函数，但实际上它无法使用。

code base

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

class FilterScreen extends StatefulWidget {
  static const routeNamed = '/filter';

  @override
  State<FilterScreen> createState() => _FilterScreenState();
}

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

  Widget _buildSwitchFilter(String title, String description, bool currentValue,
      Function updateValue) {
    return SwitchListTile(
        title: Text(title),
        subtitle: Text(description),
        value: currentValue,
        onChanged: (val) => updateValue);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        drawer: MainDrawer(),
        appBar: AppBar(),
        body: Column(
          children: [
            Expanded(
                child: ListView(
              children: [
                _buildSwitchFilter('Gluten-free',
                    'Only include gluten-free meals', _glutenFree, (newVal) {
                  setState(() {
                    _glutenFree == newVal;
                  });
                }),
                _buildSwitchFilter(
                    'Lactose-free',
                    'Only include lactose-free meals',
                    _glutenFree,
                    (newVal) => _lactoseFree == newVal),
                _buildSwitchFilter(
                    'Vegan-free',
                    'Only include vegan-free meals',
                    _glutenFree,
                    (newVal) => _vegan == newVal),
                _buildSwitchFilter(
                    'Vegetarian-free',
                    'Only include vegetarian-free meals',
                    _glutenFree,
                    (newVal) => _vegetarian == newVal),
              ],
            ))
          ],
        ));
  }
}

Answer 1

这是不正确的

_glutenFree == newVal;

== 是一个相等运算符 https://api.dart.dev/be/137051/dart-core/Object/operator_equals.html

你需要的是使用 =

赋值

正确:

_glutenFree = newVal;

对其他人做同样的事情