Passing variable value from state to another widget

Question

I am struggling with one simple case and it would be lovely if someone could help here.

Let's say that I have some stateful widget . In its state I define a variable (might be of any type) and this variable is later changed through setState() method, where I dynamically assign its value based on some certain criteria. Evertyhing until this point is conducted within one class.

What if I would like to access the value of this variable from another class (totally different page ) and if its value changes, rebuild it? Could you please also give me some examples?

Thanks in advance!

Answer 1

That's exactly why State MANAGEMENT exists. To manage your state through your app. There are many different options to follow See: https://flutter.dev/docs/development/data-and-backend/state-mgmt/options

Answer 2

You can use provider package in that case. In yaml file add, provider: ^4.3.2+4

class HomeApp extends StatefulWidget {
  @override
  _HomeAppState createState() => _HomeAppState();
}

class _HomeAppState extends State<HomeApp> {
  Counter _counterProvider;

  @override
  void initState() {
    super.initState();
    _counterProvider = Provider.of(context, listen: false);
  }

  void updateCounter() {
    _counterProvider.setCount();
  }

  @override
  Widget build(BuildContext context) {
    Counter _counterProvider = Provider.of(context);
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Container(
              child: Text(
                _counterProvider.count.toString(),
                style: TextStyle(
                  fontSize: 22,
                ),
              ),
            ),
            RaisedButton(
              onPressed: updateCounter,
              child: Text('Click'),
            ),
          ],
        ),
      ),
    );
  }
}

// class for storing data(Counter.dart)
import 'package:flutter/material.dart';

class Counter extends ChangeNotifier { // create a common file for data
  int _count = 0;

  int get count => _count;

  void setCount() {
    _count++;
    notifyListeners();
  }
}