Flutter Button Formatting and Passing Call back Function

We had already created a new widget for questions. Now, we’ll create a new widget for answers. 

Create a new file answer.dart besides main.dart and add the following code there.

//FileName: answer.dart
import 'package:flutter/material.dart';

class Answer extends StatelessWidget {
  final Function selectHandler;

  Answer(this.selectHandler);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity, ////double.infinity means occupy the whole screen (width in this case)
      margin: EdgeInsets.all(10), //apply margin of 10 pts to all 4 sides
      /*
      * We have provided 3 named arguments here to ElevatedButton()
      * 1. child: which is a Text() widget
      * 2. onPressed: which is a function we get via constructor
      * 3. style: where we change the color, padding and text style
       */
      child: ElevatedButton(
        child: Text('Answer1'),
        //onPressed takes a function
        onPressed: selectHandler,
        style: ElevatedButton.styleFrom(
          primary: Colors.blue, //the button's background color
          onPrimary: Colors.white, //the button's text color

          padding: EdgeInsets.symmetric(horizontal: 50, vertical: 20),
          textStyle: TextStyle(fontSize: 30, fontWeight: FontWeight.bold),
        ), //.styleFrom
      ), //ElevatedButton
    ); //Container
  }
}

Here is question.dart file previously created.

//FileName: question.dart
import 'package:flutter/material.dart';

class Question extends StatelessWidget {
  /*
  * final keywords tells dart that this value will never change after its
  * initialization here int he constructor
   */
  final String questionText;

  /* Lets have a constructor to initialize this widget class questionText
  *  Now the first positional argument passed to this constructor will be stored in
  *  questionText variable
   */
  Question(this.questionText);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity, //double.infinity means occupy the whole screen (width in this case)
      margin: EdgeInsets.all(10), //apply margin of 10 pts to all 4 sides
      child: Text(
        questionText,
        style: TextStyle(fontSize: 26),
        textAlign: TextAlign.center,
      ), //Text
    ); //Container()
  } //build
} //Question

In our main.dart file we’ll add the import for answer.dart and will replace ElevatedButton() code with this Answer() code and will add SizedBox() for spacing.

Now, our main.dart file’s code is simple and easy to understand.

//File Name: main.dart
import 'package:flutter/material.dart';

/* ./ means look in the main folder where main.dart resides and then the
*  name of the file which you wana import
 */

import './question.dart';
import './answer.dart';

/*
* The arrow function allows us to create a simplified function consisting of a single expression.
* We can omit the curly brackets and the return keyword
*/

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

class MyApp extends StatefulWidget {
  /*
   * createState() is a method that takes no arguments but returns a State object
   * which is connected to a StatefulWidget
   */
  @override
  State<StatefulWidget> createState() {
    return _MyAppState();
  } //createState()
} //StatefulWidget

/* A leading underscore makes the property private, here leading underscore will turn
 * this public class in to private class. Now MyAppState class can only be used in
 * main.dart file, in our case in MyApp class.
 */
class _MyAppState extends State<MyApp> {
  var _questionIndex = 0;

  void _answerQuestion() {
    setState(() {
      _questionIndex++;
    });
    print(_questionIndex);
  }

  @override
  Widget build(BuildContext context) {
    var questions = [
      'What\'s your favorite color?',
      'What\'s your favorite animal?'
    ];
    return MaterialApp(
      /*
      * A Scaffold Widget provides a framework which implements the basic material design visual
      * layout structure of the flutter app.
       */
      home: Scaffold(
        appBar: AppBar(
          title: Text('First Flutter App'),
        ),
        body: Column(
          children: <Widget>[
            Question(
              questions[_questionIndex],
            ),
            Answer(_answerQuestion),
            SizedBox(height: 16),
            Answer(_answerQuestion),
            SizedBox(height: 16),
            Answer(_answerQuestion),
          ],
        ),
      ),
    );
  } //build()
} //MyApp()
Output

This is a lot to digest but I have made things easy to understand by taking you along using step by step approach.

Happy Coding!