How to pass data from one dart class to another in flutter ?

How to use data in another dart class?

In Flutter, you can pass data from one Dart class to another using constructor parameters

First Example:-

// FirstPage.dart
class FirstPage extends StatelessWidget {
  final String data;

  FirstPage({Key key, @required this.data}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('First Page'),
      ),
      body: Center(
        child: Text(data),
      ),
    );
  }
}

// SecondPage.dart
class SecondPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    String data = 'Hello, World!';
    return Scaffold(
      appBar: AppBar(
        title: Text('Second Page'),
      ),
      body: Center(
        child: ElevatedButton(
          onPressed: () {
            Navigator.push(
              context,
              MaterialPageRoute(
                builder: (context) => FirstPage(data: data),// here data 
// value is pass
              ),
            );
          },
          child: Text('Go to First Page'),
        ),
      ),
    );
  }
}

// MyApp.dart
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: SecondPage(),
    );
  }
}

In this example, the SecondPage has a button that navigates to the FirstPage and passes the data parameter through its constructor. The FirstPage receives the data and displays it in the UI.

Second Example :-

// FirstPage.dart
class FirstPage extends StatelessWidget {
  final String data;

  FirstPage({Key key, @required this.data}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('First Page'),
      ),
      body: Center(
        child: TextField(
          controller: TextEditingController(text: data),
          decoration: InputDecoration(
            labelText: 'Enter Data',
          ),
        ),
      ),
    );
  }
}

// SecondPage.dart
class SecondPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    String data = 'Hello, World!';
    return Scaffold(
      appBar: AppBar(
        title: Text('Second Page'),
      ),
      body: Center(
        child: ElevatedButton(
          onPressed: () {
            Navigator.push(
              context,
              MaterialPageRoute(
                builder: (context) => FirstPage(data: data),
              ),
            );
          },
          child: Text('Go to First Page'),
        ),
      ),
    );
  }
}

// MyApp.dart
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: SecondPage(),
    );
  }
}

In this example, the SecondPage has a button that navigates to the FirstPage and passes the data parameter through its constructor. The FirstPage receives the data and sets it as the initial value of a TextField.