Flutter Focus/Builder usage

main.dart

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

/// This is the main application widget.
class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: const MyStatelessWidget(),
      ),
    );
  }
}
/// This is the private State class that goes with MyStatefulWidget.
class MyStatelessWidget extends StatelessWidget {
  
  const MyStatelessWidget();
  
  @override
  Widget build(BuildContext context) {
    return FocusScope(
      debugLabel: 'Scope',
      autofocus: true,
      child: Form(
        child: Column(
          children: [
            Focus(
              debugLabel: 'TextField1',
              child: Builder(
                builder: (BuildContext context) {
                  final FocusNode focusNode = Focus.of(context);
                  final bool hasFocus = focusNode.hasFocus;
                  return TextField(
                    decoration: InputDecoration(
                      fillColor: hasFocus ? Colors.green : Colors.white,
                      filled: true
                    )
                  );
                },
              ),
            ),
            Focus(
              debugLabel: 'TextField2',
              child: Builder(
                builder: (BuildContext context) {
                  final FocusNode focusNode = Focus.of(context);
                  final bool hasFocus = focusNode.hasFocus;
                  return TextField(
                    decoration: InputDecoration(
                      fillColor: hasFocus ? Colors.green : Colors.white,
                      filled: true
                    )
                  );
                }
              )
            )
          ],
        ),
      ),
    );
  }
}