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Basic widgets
Flutter comes with a suite of powerful basic widgets,
of which the following are commonly used:Below are some simple widgets that combine these and other widgets:
<code_start>import 'package:flutter/material.dart';
class MyAppBar extends StatelessWidget {
const MyAppBar({required this.title, super.key});
// Fields in a Widget subclass are always marked "final".
final Widget title;
@override
Widget build(BuildContext context) {
return Container(
height: 56, // in logical pixels
padding: const EdgeInsets.symmetric(horizontal: 8),
decoration: BoxDecoration(color: Colors.blue[500]),
// Row is a horizontal, linear layout.
child: Row(
children: [
const IconButton(
icon: Icon(Icons.menu),
tooltip: 'Navigation menu',
onPressed: null, // null disables the button
),
// Expanded expands its child
// to fill the available space.
Expanded(
child: title,
),
const IconButton(
icon: Icon(Icons.search),
tooltip: 'Search',
onPressed: null,
),
],
),
);
}
}
class MyScaffold extends StatelessWidget {
const MyScaffold({super.key});
@override
Widget build(BuildContext context) {
// Material is a conceptual piece
// of paper on which the UI appears.
return Material(
// Column is a vertical, linear layout.
child: Column(
children: [
MyAppBar(
title: Text(
'Example title',
style: Theme.of(context) //
.primaryTextTheme
.titleLarge,
),
),
const Expanded(
child: Center(
child: Text('Hello, world!'),
),
),
],
),
);
}
}
void main() {
runApp(
const MaterialApp(
title: 'My app', // used by the OS task switcher
home: SafeArea(
child: MyScaffold(),
),
),
);
}<code_end>
Be sure to have a uses-material-design: true entry in the flutter
section of your pubspec.yaml file. It allows you to use the predefined
set of Material icons. It’s generally a good idea to include this line
if you are using the Materials library.Many Material Design widgets need to be inside of a MaterialApp
to display properly, in order to inherit theme data.
Therefore, run the application with a MaterialApp.The MyAppBar widget creates a Container with a height of 56
device-independent pixels with an internal padding of 8 pixels,
both on the left and the right. Inside the container,
MyAppBar uses a Row layout to organize its children.
The middle child, the title widget, is marked as Expanded,
which means it expands to fill any remaining available space
that hasn’t been consumed by the other children.
You can have multiple Expanded children and determine the
ratio in which they consume the available space using the
flex argument to Expanded.The MyScaffold widget organizes its children in a vertical column.
At the top of the column it places an instance of MyAppBar,
passing the app bar a Text widget to use as its title.
Passing widgets as arguments to other widgets is a powerful technique
that lets you create generic widgets that can be reused in a wide
variety of ways. Finally, MyScaffold uses an
Expanded to fill the remaining space with its body,
which consists of a centered message.For more information, check out Layouts.<topic_end>
<topic_start>
Using Material Components
Flutter provides a number of widgets that help you build apps