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Flutter_Documentation

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),
body: Center(child: Text(textToShow)),
floatingActionButton: FloatingActionButton(
onPressed: _updateText,
tooltip: 'Update Text',
child: const Icon(Icons.update),
),
);
}
}<code_end>
<topic_end>
<topic_start>
How do I lay out my widgets? Where is my XML layout file?
In Android, you write layouts in XML, but in Flutter you write your layouts
with a widget tree.The following example shows how to display a simple widget with padding:
<code_start>@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Sample App'),
),
body: Center(
child: ElevatedButton(
style: ElevatedButton.styleFrom(
padding: const EdgeInsets.only(left: 20, right: 30),
),
onPressed: () {},
child: const Text('Hello'),
),
),
);
}<code_end>
You can view some of the layouts that Flutter has to offer in the
widget catalog.<topic_end>
<topic_start>
How do I add or remove a component from my layout?
In Android, you call addChild() or removeChild()
on a parent to dynamically add or remove child views.
In Flutter, because widgets are immutable there is
no direct equivalent to addChild(). Instead,
you can pass a function to the parent that returns a widget,
and control that child’s creation with a boolean flag.For example, here is how you can toggle between two
widgets when you click on a FloatingActionButton:
<code_start>import 'package:flutter/material.dart';
void main() {
runApp(const SampleApp());
}
class SampleApp extends StatelessWidget {
const SampleApp({super.key});
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Sample App',
theme: ThemeData(
colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
),
home: const SampleAppPage(),
);
}
}
class SampleAppPage extends StatefulWidget {
const SampleAppPage({super.key});
@override
State<SampleAppPage> createState() => _SampleAppPageState();
}
class _SampleAppPageState extends State<SampleAppPage> {
// Default value for toggle.
bool toggle = true;
void _toggle() {
setState(() {
toggle = !toggle;
});
}
Widget _getToggleChild() {
if (toggle) {
return const Text('Toggle One');
} else {
return ElevatedButton(
onPressed: () {},
child: const Text('Toggle Two'),
);
}
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Sample App'),
),
body: Center(
child: _getToggleChild(),
),
floatingActionButton: FloatingActionButton(
onPressed: _toggle,
tooltip: 'Update Text',
child: const Icon(Icons.update),
),
);
}