How to use initState from another file on flutter?

Question

I'm trying to import the information of initState that stores the state of my Switch.

The problem is that initState is on my homepage file and I want to import it from my "error page".

Example:

If my Switch is on, my theme will change.
I want to import that Switch info (boolean) on every page of my app.
I want to be able to change that Switch value on other pages too.

Here is my homepage:

class _MyHomePageState extends State\ {
bool isSwitchedFT = false;
void updateSwitchValue(bool newValue)
  {
    setState(() {
      isSwitchedFT = newValue;
    });
  }

@override
void initState(){
super.initState();
getSwitchValues();
}
getSwitchValues() async {
isSwitchedFT = (await getSwitchState())!;
setState(() {});
}

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

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

    return isSwitchedFT;

}

@override
Widget build(BuildContext context) {
return Scaffold(){...}

And here is my other page:

class _ErrorPageState extends State {

/// I want to get this boolean info from MyHomePage initState
   bool isSwitchedFT = false;

  @override
  Widget build(BuildContext context) {
    return SafeArea(
        child: Scaffold(...);

Here is my Switch:

Switch(
                  value: isSwitchedFT,
                  onChanged: (bool value) {
                    setState(() {
                      isSwitchedFT = value;
                      saveSwitchState(value);
                      //switch works
                    });
                  })

this is my complete code from the second page:

class SubmitErrorPage extends StatelessWidget {
  const SubmitErrorPage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: ErrorPage(),
    );
  }
}

class ErrorPage extends StatefulWidget {


  const ErrorPage({Key? key}) : super(key: key);

  @override
  State createState() => ErrorPageState();
}

class ErrorPageState extends State {


  bool isSwitchedFT = true;

  GlobalKey myKey = GlobalKey();
  //get the value of the switch
  bool getSwitchValueFromHomePage()
  {
    return myKey.currentState!.isSwitchedFT;
  }
  //update the switch
  void updateSwitchValue(bool newValue)
  {
    myKey.currentState!.updateSwitchValue(newValue); // you need to implement this function in your MyHomePageState
  }



  @override
  Widget build(BuildContext context) {
    return SafeArea(
child: Scaffold(
          backgroundColor: isSwitchedFT ? Colors.black : Colors.white,){...}

user_9585771 · Answer

you access the variable from your state using GlobalKey like:

 static GlobalKey myKey = GlobalKey();

 myKey.currentState!.isSwitchedFT; //here

where you have to remove the _ part from your state to be accessible.

edit: the logic in your code would look something like:

class _ErrorPageState extends State {

  /// I want to get this boolean info from MyHomePage initState
  bool isSwitchedFT = false;
  GlobalKey myKey = GlobalKey();
  //get the value of the switch 
  bool getSwitchValueFromHomePage()
  {
    return myKey.currentState!.isSwitchedFT;
  }
  //update the switch
  void updateSwitchValue(bool newValue)
  {
    myKey.currentState!.updateSwitchValue(newValue); // you need to implement this function in your MyHomePageState
  }
  
  @override
  Widget build(BuildContext context) {
    return SafeArea(
        child: Scaffold(...);
  }
}

the updateSwitchValue would look like:

void updateSwitchValue(bool newValue)
{
  setState(() {
       this.isSwitchedFT = newValue;
    });
}

and you need to add it to your MyHomePageState.

How to use initState from another file on flutter?

1 Answers