Flutter How to set Boolean from Settingpage

How to turn On/Off vibration on Homepage from Settings page with boolean SwitchListTile?

I want if the SwitchListTile in the Settings page is On, the Homepage will vibrate every time I tap it, and vice versa. basically I don't know how to control certain pages from other pages

this is MySettingPage

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

class MySettingPage extends StatefulWidget {
  const MySettingPage({Key key}) : super(key: key);

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

class _MySettingPageState extends State<MySettingPage> {
  bool isVibrate = false;

  @override
  void initState() {
    super.initState();
    getSwitchValues();
  }

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

  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();
    bool isVibrate = prefs.getBool("switchState");
    return isVibrate;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        titleSpacing: 0,
        title: Text("Pengaturan"),
        leading: IconButton(
            icon: Icon(Icons.arrow_back),
            onPressed: () {
              Navigator.of(context).pop();
            }),
      ),
      body: Container(
        padding: EdgeInsets.all(10),
        child: ListView(
          children: [
            SwitchListTile(
              title: Text("Getar"),
              value: isVibrate,
              onChanged: (bool value) async {
                setState(() {
                  isVibrate = value;
                  saveSwitchState(value);
                });
              },
            ),
            //
          ],
        ),
      ),
    );
  }
}

this is MyHomePage

import 'package:flutter/material.dart';
import 'package:vibration/vibration.dart';
import 'mysettingpage.dart';

class MyHomePage extends StatefulWidget {
  final bool isVibrate;
  MyHomePage({Key key, this.isVibrate}) : super(key: key);
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  void _incrementCounter() {
    setState(() {
      _counter++;
      if (widget.isVibrate == true) {
        Vibration.vibrate(duration: 70);
      }
      if (widget.isVibrate == false) {
        Vibration.cancel();
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("My Homepage"),
        titleSpacing: 0,
        leading: IconButton(
          icon: Icon(Icons.settings),
          onPressed: () {
            Navigator.push(
                context,
                MaterialPageRoute(
                  builder: (BuildContext context) => MySettingPage(),
                ));
          },
        ),
      ),
      body: GestureDetector(
        onTap: () {
          _incrementCounter();
        },
        child: Container(
          height: double.infinity,
          width: double.infinity,
          child: Padding(
            padding: const EdgeInsets.only(bottom: 120),
            child: Column(
              children: [
                Expanded(
                  child: Column(
                    crossAxisAlignment: CrossAxisAlignment.center,
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: [
                      Padding(
                        padding: EdgeInsets.symmetric(horizontal: 20),
                        child: FittedBox(
                          child: Text(
                            '$_counter',
                            textAlign: TextAlign.center,
                            style: TextStyle(
                              fontSize: 200,
                              fontFamily: 'DS-Digital',
                              color: Color(0xFF24F3E2),
                            ),
                          ),
                        ),
                      ),
                    ],
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

To continue on the response from Allan C with the changes to your code: (untested)

HomePage:

import 'package:flutter/material.dart';
import 'package:vibration/vibration.dart';
import 'mysettingpage.dart';

class MyHomePage extends StatefulWidget {
  final bool isVibrate;
  MyHomePage({Key key, this.isVibrate}) : super(key: key);
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  bool _isVibrate;

  @override
  void initState() {
    super.initState();

    _isVibrate = widget.isVibrate;
  }

  void _onVibrateChange(bool value) {
    setState(() {
      _isVibrate = value;
    })
  }

  void _incrementCounter() {
    setState(() {
      _counter++;
      if (_isVibrate) {
        Vibration.vibrate(duration: 70);
      }
      if (_isVibrate) {
        Vibration.cancel();
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("My Homepage"),
        titleSpacing: 0,
        leading: IconButton(
          icon: Icon(Icons.settings),
          onPressed: () {
            Navigator.push(
                context,
                MaterialPageRoute(
                  builder: (BuildContext context) => MySettingPage(
                    onChange: _onVibrateChange
                  ),
                ));
          },
        ),
      ),
      body: GestureDetector(
        onTap: () {
          _incrementCounter();
        },
        child: Container(
          height: double.infinity,
          width: double.infinity,
          child: Padding(
            padding: const EdgeInsets.only(bottom: 120),
            child: Column(
              children: [
                Expanded(
                  child: Column(
                    crossAxisAlignment: CrossAxisAlignment.center,
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: [
                      Padding(
                        padding: EdgeInsets.symmetric(horizontal: 20),
                        child: FittedBox(
                          child: Text(
                            '$_counter',
                            textAlign: TextAlign.center,
                            style: TextStyle(
                              fontSize: 200,
                              fontFamily: 'DS-Digital',
                              color: Color(0xFF24F3E2),
                            ),
                          ),
                        ),
                      ),
                    ],
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

using the initState() you set a default value of _isVibrate from the passed value from the widget.isVibrate.

The method _onVibrateChange(bool value) (as a callback) will update the local variable within the state. This method needs to be passed to the MySettingsPage also.

MySettingsPage:

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

class MySettingPage extends StatefulWidget {
  const MySettingPage({Key key, this.onChange}) : super(key: key);

  final Function(bool value) onChange;

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

class _MySettingPageState extends State<MySettingPage> {
  bool isVibrate = false;

  @override
  void initState() {
    super.initState();
    getSwitchValues();
  }

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

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

  Future<bool> getSwitchState() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    bool isVibrate = prefs.getBool("switchState");
    return isVibrate;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        titleSpacing: 0,
        title: Text("Pengaturan"),
        leading: IconButton(
            icon: Icon(Icons.arrow_back),
            onPressed: () {
              Navigator.of(context).pop();
            }),
      ),
      body: Container(
        padding: EdgeInsets.all(10),
        child: ListView(
          children: [
            SwitchListTile(
              title: Text("Getar"),
              value: isVibrate,
              onChanged: (bool value) async {
                setState(() {
                  isVibrate = value;
                  saveSwitchState(value);
                });
              },
            ),
            //
          ],
        ),
      ),
    );
  }
}

I have included a new variable passed to the Statefulwidget (Function(bool value) onChange), this will be the callback for when the switch changes it's value.

In the method Future saveSwitchState(bool value) async there is a call to the passed callback with the updated value from the SwitchListTiles onChange method.

Hope this clarifies what he meant in his answer.