ValueListenableBuilder<T>

 

ValueNotifier 선언
final ValueNotifier<int> _counter = ValueNotifier<int>(0);


데이터 커스텀 알리미..

//데이터 선언
class MyValuesObject{
  String name;
  int age;
  ui.Image? thumbnail;
}


//알리미 선언
class MyNotifier extends ValueNotifier<MyValuesObject>{
  MyNotifier(MyValuesObject value) : super(value);
}

==>ValueNotifier 에는 value getter/setter와 tostring() 만 있음.
     상위 클래스로 가면 notify관련 메소드들이 있음.

//알리미 변수 선언
final MyNotifier  _myNotifier = MyNotifier(MyValuesObject());

 

 

 

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}


class MyHomePage extends StatelessWidget {

  final ValueNotifier<int> _counter = ValueNotifier<int>(0);
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
          title: Text("aaaaaa")
      ),
      body: Center(
        child: ValueListenableBuilder<int>(
          builder: (BuildContext context, int value, Widget? child) {
            //_counter가 업데이트 될때만 builder 함수가 호출됨
            return Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: <Widget>[
                Text('$value'),
                child!, //밑에 파라미터로 넘긴 child
              ],
            );
          },
          valueListenable: _counter,
          child: const Text('Good job!'),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        child: const Icon(Icons.plus_one),
        onPressed: () => _counter.value += 1,
      ),
    );
  }
}

 

https://api.flutter.dev/flutter/widgets/ValueListenableBuilder-class.html

 

 

https://medium.com/flutter-community/flutter-notifications-bubble-up-and-values-go-down-c1a499d22d5f