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@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 placeholder text. |
string textToShow = 'i like flutter'; |
void _updateText() { |
setState(() { |
// update the text. |
textToShow = 'flutter is awesome!'; |
}); |
} |
@override |
widget build(BuildContext context) { |
return scaffold( |
appBar: AppBar( |
title: const Text('Sample app'), |
), |
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鈥檚 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}); |