Introduction

Flutter is Google's framework for building apps from a single codebase: write once in Dart, and ship to iOS, Android, web, Windows, macOS, and Linux. It powers apps from Google Pay to the New York Times crossword app. Its core idea is simple and radical: everything on screen is a widget, and the interface is rebuilt from data whenever that data changes.

Everything is a widget

In Flutter, there are no separate concepts for layout, styling, and controls — everything is a widget, nested inside other widgets like HTML elements, but in code:

import 'package:flutter/material.dart' ; class Greeting extends StatelessWidget { @override Widget build ( BuildContext context ) { return Center ( child: Text ( 'Hello, Sara!' , style: TextStyle ( fontSize: 24 , color: Colors . teal ), ), ); } }

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Center positions its child, Text displays words, TextStyle styles them — each a widget, composed by nesting.…