ValueListenableBuilder
snippet.packages.flutter.lib.src.widgets.value_listenable_builder.49.
// ignore_for_file: directives_ordering
// ignore_for_file: unnecessary_import
// ignore_for_file: unused_import
// ignore_for_file: unused_element
// ignore_for_file: unused_local_variable
import 'dart:async';
import 'dart:convert';
import 'dart:math' as math;
import 'dart:typed_data';
import 'dart:ui' as ui;
import 'package:flutter_test/flutter_test.dart';
import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/painting.dart';
import 'package:flutter/physics.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/semantics.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/scheduler.dart';
import 'package:flutter/animation.dart';
import 'package:flutter/services.dart';
// From: packages/flutter/lib/src/widgets/value_listenable_builder.dart:49
class MyHomePage extends StatefulWidget {
const MyHomePage({Key? key, required this.title}) : super(key: key);
final String title;
@override
State createState() => _MyHomePageState();
}
class _MyHomePageState extends State {
final ValueNotifier _counter = ValueNotifier(0);
final Widget goodJob = const Text('Good job!');
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title)
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
const Text('You have pushed the button this many times:'),
ValueListenableBuilder(
builder: (BuildContext context, int value, Widget? child) {
// This builder will only get called when the _counter
// is updated.
return Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: [
Text('$value'),
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: goodJob,
)
],
),
),
floatingActionButton: FloatingActionButton(
child: const Icon(Icons.plus_one),
onPressed: () => _counter.value += 1,
),
);
}
}
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