flutter-一个可以输入的数字增减器

以下是一个简单的Flutter数字增减器示例，使用TextField来输入数字，并使用IconButton来增加或减少数字。

import 'package:flutter/material.dart';
 
void main() => runApp(MyApp());
 
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}
 
class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}
 
class _HomePageState extends State<HomePage> {
  int _counter = 0;
 
  void _incrementCounter() => setState(() => _counter++);
  void _decrementCounter() => setState(() => _counter--);
 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                IconButton(
                  icon: Icon(Icons.remove),
                  onPressed: _decrementCounter,
                ),
                TextField(
                  decoration: InputDecoration(
                    border: OutlineInputBorder(),
                    hintText: '0'
                  ),
                  onSubmitted: (value) => setState(() => _counter = int.parse(value)),
                  keyboardType: TextInputType.number,
                  controller: TextEditingController()..text = '$_counter',
                ),
                IconButton(
                  icon: Icon(Icons.add),
                  onPressed: _incrementCounter,
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }
}

这段代码创建了一个简单的应用，用户可以通过点击加号或减号按钮来增加或减少数字，也可以直接在输入框中输入数字。输入框会根据当前计数器的值进行初始化。