Created
April 25, 2024 02:59
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Keeping state when widget is repositioned
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import 'package:flutter/material.dart'; | |
void main() => runApp(const MyApp()); | |
class MyApp extends StatelessWidget { | |
const MyApp({super.key}); | |
@override | |
Widget build(BuildContext context) { | |
return MaterialApp( | |
title: 'Flutter Demo', | |
home: MyHomePage(), | |
); | |
} | |
} | |
class MyHomePage extends StatefulWidget { | |
@override | |
State<MyHomePage> createState() => _MyHomePageState(); | |
} | |
class _MyHomePageState extends State<MyHomePage> { | |
bool _isBaz = true; | |
@override | |
Widget build(BuildContext context) { | |
return Scaffold( | |
body: Foo(child: Counter(), isBaz: _isBaz), | |
floatingActionButton: FloatingActionButton( | |
onPressed: () => setState(() => _isBaz = !_isBaz), | |
tooltip: 'Toggle isBaz', | |
child: const Icon(Icons.ac_unit), | |
), | |
); | |
} | |
} | |
class Counter extends StatefulWidget { | |
@override | |
State<Counter> createState() => _CounterState(); | |
} | |
class _CounterState extends State<Counter> { | |
int _counter = 0; | |
@override | |
Widget build(BuildContext context) { | |
return Scaffold( | |
body: Center( | |
child: Column( | |
mainAxisAlignment: MainAxisAlignment.center, | |
children: [ | |
const Text( | |
'You have pushed the button this many times:', | |
), | |
Text( | |
'$_counter', | |
style: Theme.of(context).textTheme.headlineMedium, | |
), | |
], | |
), | |
), | |
floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat, | |
floatingActionButton: FloatingActionButton( | |
onPressed: () => setState(() => _counter += 1), | |
tooltip: 'Increment', | |
child: const Icon(Icons.add), | |
), | |
); | |
} | |
} | |
class Foo extends StatefulWidget { | |
final Widget child; | |
final bool isBaz; | |
const Foo({required this.child, required this.isBaz}); | |
@override | |
State<Foo> createState() => FooState(); | |
} | |
class FooState extends State<Foo> { | |
final _key = GlobalKey(); | |
@override | |
Widget build(BuildContext context) { | |
// Removing the `_key` or the `KeyedSubtree` causes `child` to be | |
// disposed and recreated when `isBaz` changes. | |
if (widget.isBaz) { | |
return KeyedSubtree(key: _key, child: widget.child); | |
} | |
return Container(child: KeyedSubtree(key: _key, child: widget.child)); | |
} | |
} |
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