如何向Flutter中的類添加多個void方法？（缺少“State.build”的具體實作。）

我是 Flutter 的初學者，我正在構建一個計數器應用程式，我想添加“清除”和“減少”的功能，而不僅僅是增加點擊時的計數器。我認為在 MyHomePage 類中添加另外兩個方法是合乎邏輯的，但它給了我錯誤

缺少“State.build”的具體實作。

我以另一種方式處理我的代碼，但是如果我想在該類中呼叫一個方法來做到這一點呢？這是我的代碼

import 'package:flutter/material.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        title: "Hello Code Palace",
        theme: ThemeData(primarySwatch: Colors.deepPurple),
        home: MyHomePage(title: "Hello app!"));
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

   void _incrementCounter() {
    setState(() {
        _counter;
    });
   /*void _decreaseCounter() {
      setState(() {
        --_counter;
      });*/
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(widget.title)),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text("The button has been pressed"),
            Text(
              " $_counter times",
              style: new TextStyle(fontSize: 30.0),
            )
          ],
        ),
      ),
      floatingActionButton: Stack(children: <Widget>[
        Padding(
          padding: const EdgeInsets.only(right: 30.0, bottom: 24.0),
          child: FloatingActionButton(
            onPressed:  ()=>setState(()=> --_counter),
            tooltip: "Decrease",
            child: Icon(Icons.remove),
          ),
        ),
        Padding(
          padding: const EdgeInsets.only(left: 265.0, bottom: 24.0),
          child: FloatingActionButton(
            onPressed: _incrementCounter,
            tooltip: "Increase",
            child: Icon(Icons.add),
          ),
        ),
        Padding(
          padding: const EdgeInsets.only(left: 130.0, bottom: 24.0),
          child: FloatingActionButton(
            onPressed: ()=>setState(()=> _counter = 0),
            tooltip: "Increase",
            child: Icon(Icons.clear_all),
          ),
        ),
      ]),
    );
  }
}

如果您看到一種以更有條理的方式排列底部按鈕的方法，我也會很感激。

uj5u.com熱心網友回復：

您應該在_incrementCounter().

請檢查以下代碼：

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

   void _incrementCounter() {
    setState(() {
        _counter;
    });
  }

   void _decreaseCounter() {
      setState(() {
        --_counter;
      });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      ...
    );
  }
}

標籤：扑 镖

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