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Inherited Widget Example - by Simon Lightfoot - Humpday Q&A :: 22nd November 2023 #Flutter #Dart
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// MIT License | |
// | |
// Copyright (c) 2023 Simon Lightfoot | |
// | |
// Permission is hereby granted, free of charge, to any person obtaining a copy | |
// of this software and associated documentation files (the "Software"), to deal | |
// in the Software without restriction, including without limitation the rights | |
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | |
// copies of the Software, and to permit persons to whom the Software is | |
// furnished to do so, subject to the following conditions: | |
// | |
// The above copyright notice and this permission notice shall be included in all | |
// copies or substantial portions of the Software. | |
// | |
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | |
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | |
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | |
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | |
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | |
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE | |
// SOFTWARE. | |
// | |
import 'package:flutter/foundation.dart'; | |
import 'package:flutter/material.dart'; | |
void main() { | |
runApp(const App()); | |
} | |
class CounterModel { | |
CounterModel({this.value = 0}); | |
int value; | |
@override | |
bool operator ==(Object other) => | |
identical(this, other) || | |
other is CounterModel && | |
runtimeType == other.runtimeType && | |
value == other.value; | |
@override | |
String toString() { | |
return '${describeIdentity(this)}{$value}'; | |
} | |
} | |
class App extends StatelessWidget { | |
const App({super.key}); | |
@override | |
Widget build(BuildContext context) { | |
return InheritedCounter( | |
child: MaterialApp( | |
debugShowCheckedModeBanner: false, | |
theme: ThemeData.dark(), | |
home: const Home(), | |
), | |
); | |
} | |
} | |
class InheritedCounter extends StatefulWidget { | |
const InheritedCounter({ | |
super.key, | |
required this.child, | |
}); | |
final Widget child; | |
static InheritedCounterState of(BuildContext context) { | |
return context | |
.dependOnInheritedWidgetOfExactType<_InheritedCounterScope>()! | |
.state; | |
} | |
@override | |
State<InheritedCounter> createState() => InheritedCounterState(); | |
} | |
class InheritedCounterState extends State<InheritedCounter> { | |
var counter = CounterModel(); | |
void add() { | |
setState(() { | |
counter.value++; | |
}); | |
} | |
@override | |
Widget build(BuildContext context) { | |
return _InheritedCounterScope( | |
state: this, | |
counter: counter, | |
child: widget.child, | |
); | |
} | |
} | |
class _InheritedCounterScope extends InheritedWidget { | |
_InheritedCounterScope({ | |
required this.state, | |
required this.counter, | |
required super.child, | |
}) : value = counter.value; | |
final InheritedCounterState state; | |
final CounterModel counter; | |
late final int value; | |
@override | |
bool updateShouldNotify(_InheritedCounterScope oldWidget) { | |
print('counter value $value'); | |
print('oldWidget value ${oldWidget.value}'); | |
return value != oldWidget.value; | |
} | |
} | |
class Home extends StatelessWidget { | |
const Home({super.key}); | |
@override | |
Widget build(BuildContext context) { | |
return Scaffold( | |
appBar: AppBar( | |
title: const Text('Inherited Counter'), | |
), | |
body: const Center( | |
child: CounterDisplay(), | |
), | |
floatingActionButton: const CounterAddButton(), | |
); | |
} | |
} | |
class CounterAddButton extends StatelessWidget { | |
const CounterAddButton({super.key}); | |
@override | |
Widget build(BuildContext context) { | |
return FloatingActionButton( | |
onPressed: InheritedCounter.of(context).add, | |
child: const Icon(Icons.add), | |
); | |
} | |
} | |
class CounterDisplay extends StatelessWidget { | |
const CounterDisplay({super.key}); | |
@override | |
Widget build(BuildContext context) { | |
final theme = Theme.of(context); | |
final counter = InheritedCounter.of(context).counter; | |
print('build display $counter'); | |
return Text( | |
'Count: ${counter.value}', | |
style: theme.textTheme.displaySmall, | |
); | |
} | |
} |
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