I am new in Flutter i need your help please,

I want to take an amount from the user and multiply it by 20 and want to show it how to do? Can someone tell me the code how it happens? if possible

This is the interface

CodePudding user response：

Here's a simple example :

import 'package:flutter/material.dart';

const Color darkBlue = Color.fromARGB(255, 18, 32, 47);

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

class App extends StatefulWidget {
  const App({Key? key}) : super(key: key);

  @override
  State<App> createState() => _AppState();
}

class _AppState extends State<App> {
  final TextEditingController controller = TextEditingController();
  int? result;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(
        scaffoldBackgroundColor: darkBlue,
      ),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: Column(
            children: [
              TextField(
                controller: controller,
              ),
              TextButton(
                child: const Text('Calculate'),
                onPressed: () {
                  setState(() {
                    result = int.parse(controller.text) * 20;
                  });
                },
              ),
              result != null ? Text(result.toString()) : Container(),
            ] 
          ),
        ),
      ),
    );
  }
}

CodePudding user response：

try below code for your desire output

Output :-

Code :-

import 'package:flutter/material.dart';

class CalculationExample extends StatefulWidget {
  const CalculationExample({Key? key}) : super(key: key);

  @override
  State<CalculationExample> createState() => _CalculationExampleState();
}

class _CalculationExampleState extends State<CalculationExample> {
  final TextEditingController controller = TextEditingController();
  int? result;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: [
          TextField(
            controller: controller,
          ),
          InkWell(
            child: const Text('Calculate'),
            onTap: () => setState(() {
              result = int.parse(controller.text) * 20;
            }),
          ),
          result != null ? Text("\$$result") : Container(),
        ],
      ),
    );
  }
}