I'm a beginner in Flutter, I'm building a counter app and I wanted to add the functionalities of "On Clear" and "Decrease" not only increase the counter on click. I thought it'd be logical to add another two methods inside the class MyHomePage but it gives me the error of

Missing concrete implementation of 'State.build'.

I work another way around my code but what if I want to call a method inside that class that does that? Here's my code

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),
          ),
        ),
      ]),
    );
  }
}

If you see a way to arrange the buttons at the bottom in a more organized way I'd appreciate that as well.

CodePudding user response：

You should add new function outside of _incrementCounter().

Please check the below code :

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(
      ...
    );
  }
}