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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