颤动切换开关和共享首选项 [英] Flutter toggle switch and shared preferences

问题描述

我需要将拨动开关的状态保存在我的应用中，并在开始时加载它.为此，我使用SharedPreferences:

I need to save the state of the toggle switch in my app and load it at the start. For that I use SharedPreferences:

Future<bool> saveSwitchState(bool value) async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  prefs.setBool("switchState", value);
  return prefs.setBool("switchState", value);
}

Future<bool> getSwitchState() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  isSwitchedFT = prefs.getBool("switchState");
  print(isSwitchedFT);

  return isSwitchedFT;
}

每次更改切换值时，saveSwitchState()都会运行.

The saveSwitchState() runs every time when I change the toggle value.

问题出在应用程序的开头. 我创建了一个布尔值:bool isSwitchedFT = false; 我初始化为false，因为null会给我错误. 我将如何设置isSwitchedFT = getSwitchState; 对于isSwitchedFT的空值，它可以编译，但是在模拟器上出现红色错误:

The problem is at the start of the app. I created a bool value: bool isSwitchedFT = false; I initialize with false because null gives me errors. How would I set isSwitchedFT = getSwitchState; On empty value for isSwitchedFT it compiles but I get a red error on my emulator:

'package:flutter/src/material/toggleable.dart': Failed assertion: line 45 pos 15: 'tristate || value
 != null': is not true.

使用值编译时，该开关可以正常工作并保存更改后的值.

when compiled with a value the switch works fine an saves the changing value.

Switch(
  value: isSwitchedFT,
  onChanged: (bool value) {
    setState(() {
      isSwitchedFT = value;
      saveSwitchState(value);
      print('Saved state is $isSwitchedFT');
      //switch works
    });
    print(isSwitchedFT);
  },
  activeTrackColor: Color(0xFF1D1F33),
  activeColor: Colors.purple[500],
),

我想要的是用开关的最后一个值加载应用程序. 谢谢.

The thing I want is to load the app with the last value of the switch. Thank you.

推荐答案

检查此代码以获取示例

class _MyAppState extends State<MyApp> {
  bool isSwitchedFT = false;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    getSwitchValues();
  }

  getSwitchValues() async {
    isSwitchedFT = await getSwitchState();
    setState(() {});
  }

  Future<bool> saveSwitchState(bool value) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.setBool("switchState", value);
    print('Switch Value saved $value');
    return prefs.setBool("switchState", value);
  }

  Future<bool> getSwitchState() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    bool isSwitchedFT = prefs.getBool("switchState");
    print(isSwitchedFT);

    return isSwitchedFT;
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Container(
          child: Center(
            child: Switch(
              value: isSwitchedFT,
              onChanged: (bool value) {
                setState(() {
                  isSwitchedFT = value;
                  saveSwitchState(value);
                  print('Saved state is $isSwitchedFT');
                  //switch works
                });
                print(isSwitchedFT);
              },
              activeTrackColor: Color(0xFF1D1F33),
              activeColor: Colors.purple[500],
            ),
          ),
        ),
      ),
    );
  }
}

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