Question

在尝试使用更改通知程序类 (code) 中定义的单个实例全局属性更改应用主题时，用于监视当前应用主题的属性 _isDark 根本不会更改，即使更改函数被执行。

尝试将其定义为实例和静态，但该属性根本不更新。

也找不到!=（不等于）operator in the Bool class

如何解决这个问题？

输出：

switchTheme()  _isDark = true
Listener -> Change Theme
switchTheme()  _isDark = true
Listener -> Change Theme
switchTheme()  _isDark = true
Listener -> Change Theme

changeTheme.dart：

import 'package:flutter/material.dart';

class MyTheme extends ChangeNotifier{

  static bool _isDark = true;//Not updating in switchTheme()
  // bool _isDark = true; //Not updating in switchTheme()


 void switchTheme(){
    _isDark != _isDark;//Avoid unnecessary statements Android Studio
    print('switchTheme()  _isDark = $_isDark');
    notifyListeners();
 }

  ThemeMode currentTheme(){
    return _isDark ? ThemeMode.dark : ThemeMode.light;
  }

config.dart：

library config.dart ;
import 'changeTheme.dart';

MyTheme myTheme = MyTheme();

homeScreen.dart :

import 'package:flutter/material.dart';
import 'config.dart';
import 'changeTheme.dart';

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

class MyApp extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        theme: ThemeData.light(),
        darkTheme: ThemeData.dark(),
        themeMode: myTheme.currentTheme(),

        home: HomeScreen(),
      );

  }
  }



class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {

  void initState(){
    super.initState();

    myTheme.addListener(() {
    print('Listener -> Change Theme');
    setState(() {

    });
    });

  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children : [
        Positioned(
          left: MediaQuery.of(context).size.width * 0.5,
          top: MediaQuery.of(context).size.height * 0.5,

          child: Container(
          width: MediaQuery.of(context).size.width * 0.1,
          height: MediaQuery.of(context).size.height * 0.05,

          child: ElevatedButton(
            onPressed: (){
              myTheme.switchTheme();
            } ,
            style: ButtonStyle(backgroundColor:  MaterialStateProperty.all(Colors.orangeAccent)),
            child: Text('Change Theme '),
          ),
      ),
        ),
     ]) );
  }
}

Answer 1

当你想切换主题时，使用 _isDark = !_isDark;（而不是 !=）来改变一个布尔值和它的对立面。

ChangeNotifier 属性不更新 (Flutter2)

1 个答案: