Flutter Basics Tutorial The ultimate beginner's guide to learning Flutter

Before we build our first app, let’s get familiar with the core UI building blocks of Flutter. This tutorial is a quick introduction to the basic building blocks of Flutter that we’ll be using throughout the rest of the course. Play around with these code samples to get a feel for how UI design in Flutter works.

Main Function

Flutter will inflate the widget passed to runApp into the root widget of the application.

file_type_flutter main.dart
import 'package:flutter/material.dart';

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

Stateless Widgets

Stateless Widgets are building blocks for the UI. They do not depend on any internal state or data. They have a build method that returns a widget - Flutter will call this method whenever the UI needs to be rendered.

file_type_flutter main.dart
class MyApp extends StatelessWidget {
  const MyApp({ Key? key }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    // return a widget here
  }
}

Material App

The MaterialApp is the root of your Flutter app. It is required to work with many built-in widgets. It also allows you to configure global routes and themes.

MaterialApp(
  theme: ThemeData(),
  routes: myRoutes,
  home: const MyHomePage(),
)

Container

A Container is a is the most layout widget. It takes a single child and allows you to control alignment, padding, margin, width, height, and more.

Tip: Use widgets like SizedBox and Padding instead of a container to make your code more readable.

Container(
  margin: EdgeInsets.all(10),
  padding: EdgeInsets.all(10),
  width: 100,
  height: 100,
  decoration: BoxDecoration(
    color: Colors.red,
    border: Border.all(
      color: Colors.black,
      width: 5,
    ),
  ),
  child: Text('Hello World'),
)

Flex Layout

Flex layout allows you to arrange widgets in a Row or a Column. It’s very similar to CSS flexbox where the parent widget controls the flow of its children. You can control individual children using the Expanded and Flexible widgets.

Col(
    children: [
        Expanded(
            child: Container(
            color: Colors.red,
            height: 100,
            ),
        ),
        Expanded(
            child: Container(
            color: Colors.green,
            height: 100,
            ),
        ),
    ]
)

Stack

A Stack is a layout widget that allows you to position widgets on top of each other. The last item in the stack will be on top.

Stack(
    children: [
        Container(
            color: Colors.red,
            width: 100,
            height: 100,
        ),
        Icon(Icons.verified)
    ],
)

List View

A ListView is a widget that displays a list of children in a scrollable view. You can control the scroll direction, physics, and more.

Create a dynamic list of items using a ListView.builder, for example:

import 'dart:math';

randomColor() {
  return Color((Random().nextDouble() * 0xFFFFFF).toInt()).withOpacity(1.0);
}

/// ...

ListView.builder(
    itemBuilder: (_, index) {
        return Container(
            color: randomColor(),
            width: 500,
            height: 500,
        );
    },
),

Stateful Widgets

Stateful widgets provide widgets with state, which is just data that changes. Use the setState() method to update the state of a widget and it will be re-rendered with the latest data.

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

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  int count = 0;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        floatingActionButton: FloatingActionButton(
          child: Icon(Icons.add),
          onPressed: () {
            setState(() {
              count++;
            });
          },
        ),
        body: Center(
          child: Text('$count'),
        ),
      ),
    );
  }
}

Basic Navigation

Use the Navigator to push and pop widgets on the navigation stack. The Scaffold class will automatically handle the back button for you.

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.green,
        title: const Text('Flutter is Fun!'),
      ),
      body: ElevatedButton(
        child: Text('Navigate'),
        onPressed: () {
          Navigator.push(
            context,
            MaterialPageRoute(
              builder: (_) => AboutScreen(),
            ),
          );
        },
      ),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('about'),
      ),
    );
  }
}

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