How to use SizedBox widget in Flutter

In this Google flutter code example we are going to learn how to use SizedBox widget in Flutter.

You can copy and adopt this source code example to your android project without reinventing the wheel.

The comments on the code provide more detailed explanation

The code is based on flutter version 1 and 2.

main.dart (App entry point)

import 'package:flutter/material.dart';
import 'sizedbox.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Baseline Widget',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        // This is the theme of your application.
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
      home: BasicSizedBox(),


import 'package:flutter/material.dart';

class BasicSizedBox extends StatelessWidget {
  //A box with a specified size
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("SizedBox Widget")),
      //the sizedBox widget forces its child to have a specific width and/or height (if that widget permits that)
      //if it doesnt contain a child, it will size itself to the given width and height
      //can also use SizedBox.expand(), which stes with and height to infinity
      //or SizedBox.fromSize() which requires a Size class

      body: Center(
        child: SizedBox(
          height: 80.0,
          width: 80.0,
          //the container has no width or height, but the sizedbox widget forces it to its own width/height
          child: Container(

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