How to get the size of text

get_textsize.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Size sizeCheck = Size.zero;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Container(
            alignment: Alignment.center,
            width: MediaQuery.of(context).size.width,
            child: Text('$sizeCheck'),
          )
        ],
      ),
      floatingActionButton: TextButton(
        child: const Text("Button"),
        onPressed: () {
          setState(() {
            TextSpan textSpan = const TextSpan(children: <TextSpan>[
              TextSpan(
                text: "123\n456\n789",
              )
            ]);
            TextPainter textPainter = TextPainter(
              text: textSpan,
              textDirection: TextDirection.ltr,
            );
            textPainter.layout(
              minWidth: 0,
              maxWidth: MediaQuery.of(context).size.width,
            );
            sizeCheck = textPainter.size;
          });
        },
      ),
    );
  }
}

https://twitter.com/dbank0208/status/1512711567124492291?s=20&t=m1lG8lPf6WdR-1PBaBLc1Q