Functions With Parameters

Part of the Making It Interactive section of Coddy's Flutter journey. Lesson 7 of 34.

A function can take a value each time you call it. That value is a parameter, written in the parentheses with its type:

void greet(String name) {
  print('Hi, $name!');
}

greet('Ada');    // Hi, Ada!
greet('Linus');  // Hi, Linus!

Inside the function, name is a variable holding whatever was passed in. One function now does the work of many.

A button cannot pass a value by itself: onPressed: wants a function with no parameters. So wrap the call in a small function with no name, the kind you met in Your First Button:

ElevatedButton(
  onPressed: () { greet('Ada'); },
  child: Text('Ada'),
)

Challenge

Easy

Replace orderTea with one function order that takes a String drink and prints One Tea, please, One Coffee, please or One Juice, please. Make all three buttons use it.

Try it yourself

import 'package:flutter/material.dart';

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

void orderTea() {
  print('One Tea, please');
}

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              ElevatedButton(onPressed: orderTea, child: Text('Tea')),
              SizedBox(height: 12),
              ElevatedButton(onPressed: () {}, child: Text('Coffee')),
              SizedBox(height: 12),
              ElevatedButton(onPressed: () {}, child: Text('Juice')),
            ],
          ),
        ),
      ),
    );
  }
}