How to use conditional statement within child attribute for Expanded Widget, Flutter

Question

I want the Expanded widget to change dependent on 'Button 1', 'Button 2' or "Button 3' is pressed. The buttons is just text wrapped in a InkWell, I can change this, but it is only for purpose of understanding how to make the Expanded to be defendant on the button push.

I have read quite a few post on this, but it is not clear to me how to do this.

IF there is a better way to do this, please tell me.

Your help is appreciated.

import 'package:flutter/material.dart';

double selectedScreen = 1;

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget middleScreen() {
    if (selectedScreen == 1) {
      return FirstScreen();
    } else if (selectedScreen == 2) {
      return SecondScreen();
    } else {
      return ThirdScreen();
    }
  }

  Container FirstScreen() {
    return Container(child: Text('FirstScreen'));
  }

  Container SecondScreen() {
    return Container(child: Text('SecondScreen'));
  }

  Container ThirdScreen() {
    return Container(child: Text('ThirdScreen'));
  }

  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [
                InkWell(
                  onTap: () {
                    selectedScreen = 1;
                  },
                  child: Column(
                    children: [
                      Text(
                        'Buttonn 1',
                      ),
                    ],
                  ),
                ),
                InkWell(
                  onTap: () {
                    selectedScreen = 2;
                  },
                  child: Column(
                    children: [
                      Text(
                        'Button 2',
                      )
                    ],
                  ),
                ),
                InkWell(
                  onTap: () {
                    selectedScreen = 3;
                  },
                  child: Column(
                    children: [
                      Text(
                        'Button 3',
                      )
                    ],
                  ),
                ),
              ],
            ),
            Container(
              height: 30,
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [Expanded(child: middleScreen())],
            )
          ],
        ),
      ),
    );
  }
}

score 0 · Accepted Answer · answered Nov 12 '22 at 21:19

Simply, due to its a stateful widget, we have to notify it's new state

The only thing you need is setState method

just wrap selectedScreen = ... parts with setState(() { ... });

A sample could be like below

setState(() { selectedScreen = 1;});

you can try it here

How to use conditional statement within child attribute for Expanded Widget, Flutter

1 Answers1