使用ValueListenableBuilder和ValueNotifier重写counter程序

import 'package:flutter/material.dart';

void main(List<String> args) {

  runApp(const MaterialApp(

    home: Homepage(),

  ));

}

class Homepage extends StatefulWidget {

  const Homepage({super.key});

  @override

  State<Homepage> createState() => _HomepageState();

}

class _HomepageState extends State<Homepage> {

  ValueNotifier<int> count = ValueNotifier<int>(0);

  @override

  Widget build(BuildContext context) {

    return Scaffold(

      body: Center(

        child: Column(

          mainAxisAlignment: MainAxisAlignment.center,

          children: [

            const Text("You clicked : "),

            ValueListenableBuilder(

              valueListenable: count,

              builder: (context, value, child) {

                return Text("${count.value}");

              },

            )

          ],

        ),

      ),

      floatingActionButton: FloatingActionButton(

        child: const Icon(Icons.add),

        onPressed: () {

          count.value = count.value + 1;

        },

      ),

    );

  }

}