The complete code of example how flutter render widgets.

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The complete code of example how flutter render widgets : Learn how Flutter render widgets

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark(useMaterial3: true),
      home: HomePage(),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);
  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {

  bool _switchTree = false;

  Widget get firstTree => Row(
    mainAxisAlignment: MainAxisAlignment.center,
    children: [
      Text("Flutter is awesome <3", style: TextStyle(fontSize: 35),),
      SizedBox(width: 10,),
    ],
  );

  Widget get secondTree => Row(
    mainAxisAlignment: MainAxisAlignment.center,
    children: [
      Text("Dart is awesome <3", style: TextStyle(fontSize: 35),),
      Padding(padding: EdgeInsets.only(right: 10),),
    ],
  );

  Widget get switchButton => Padding(
    padding: EdgeInsets.only(bottom: 20),
    child: ElevatedButton(
      onPressed: () {
        setState(() {
          _switchTree = !_switchTree;
        });
      },
      child: Text("Switch Tree"),
    ),
  );

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          _switchTree ? firstTree : secondTree,
          SizedBox(height: 10,),
          switchButton
        ],
      )
    );
  }
}