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value_listenable_builder.dart
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value_listenable_builder.dart
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import 'package:flutter/material.dart';
import 'package:flutter_widget_guide/utils.dart';
import '../Ads.dart';
import '../Code.dart';
import '../CodeScreen.dart';
class ValueListenableBuilderWidget extends StatefulWidget {
@override
_ValueListenableBuilderWidgetState createState() =>
_ValueListenableBuilderWidgetState();
}
class _ValueListenableBuilderWidgetState
extends State<ValueListenableBuilderWidget> {
/// This is the value you want your widgets to listen to.
final ValueNotifier<int> _counter = ValueNotifier<int>(2);
@override
void initState() {
//Hide banner ad if it isn't already hidden
Ads.hideBannerAd();
super.initState();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
centerTitle: true,
title: Text(
'ValueListenableBuilder Widget',
style: TextStyle(
fontSize: 20.0,
fontWeight: FontWeight.bold,
fontFamily: Utils.ubuntuRegularFont),
),
actions: <Widget>[
IconButton(
icon: Icon(Icons.code),
onPressed: () => Navigator.push(
context,
MaterialPageRoute(
builder: (context) =>
CodeScreen(code: Code.valueListenableBuilderCode),
),
),
)
],
),
body: Center(
child: ValueListenableBuilder(
builder: (BuildContext context, int value, Widget child) {
// This builder will only get called when the _counter
// is updated.
return Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Padding(
padding: const EdgeInsets.all(12.0),
child: Text(
'$value',
style:
TextStyle(fontWeight: FontWeight.bold, fontSize: 34.0),
),
),
Padding(
padding: const EdgeInsets.all(8.0),
child: Text(
'The number is now ',
style: TextStyle(
fontWeight: FontWeight.normal, fontSize: 18.0),
),
),
Padding(
padding: const EdgeInsets.all(8.0),
child: Padding(
padding: const EdgeInsets.all(8.0),
child: value.remainder(2) == 0
? Text(
"Even",
style: TextStyle(
fontWeight: FontWeight.bold, fontSize: 24.0),
)
: Text(
"Odd",
style: TextStyle(
fontWeight: FontWeight.bold, fontSize: 24.0),
),
),
),
child,
],
);
},
valueListenable: _counter,
// The child parameter is most helpful if the child is
// expensive to build and does not depend on the value from
// the notifier.
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Text("I dont care about the value"),
),
),
),
floatingActionButton: FloatingActionButton(
child: Icon(Icons.plus_one),
backgroundColor: Colors.blue,
foregroundColor: Colors.white,
onPressed: () => _counter.value += 1,
),
);
}
}