StatelessWidget

stateless_widget.dart

import 'package:flutter/material.dart';

void main() {
  final firstPageContent = Container(
    width: 400.0,
    height: 400.0,
    decoration: BoxDecoration(
      color: Colors.orange,
      shape: BoxShape.circle,
    ),
  );

  runApp(
    MyPage(title: 'Circle Page', content: firstPageContent),
  );
}

class MyPage extends StatelessWidget {
  // Stateless widget's fields should always be final
  final String title;
  final Widget content;

  // and declared as optional named parameters.
  // Use @required to mark fields that have to be
  // inited by user.
  MyPage({@required this.title, @required this.content});

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.grey[50],
      child: Column(mainAxisSize: MainAxisSize.min, children: [
        Container(
          height: 56.0,
          color: Colors.lightBlue,
          child: Center(
            child: Text(
              title,
              textDirection: TextDirection.ltr,
              style: TextStyle(color: Colors.white, fontSize: 16.0),
            ),
          ),
        ),
        Expanded(
          child: Center(child: content),
        )
      ]),
    );
  }
}