Programming Flutter: Native, Cross-Platform Apps the Easy Way

364 Pages·2020·16.664 MB·English

by  Carmine Zaccagnino

Early Praise for Programming Flutter
I’m excited to read this book: ten years ago, I learned Android development reading
a PragProg book, and this has changed my life forever. Now this book could change
it again.
➤ Giordano Scalzo
iOS Senior Software Engineer, NatWest Markets
Carmine’s book is a comprehensive journey into Flutter. He leads you through
the basics like widgets, standard library, packages, and plugins, and helps you
to understand the more advanced topics like network, I/O, navigation, testing,
debugging, and firebase. His book is a reference for practical suggestions, useful
tips, and solid advice, without sacrificing the details. What I liked the most is that
each chapter starts with a premise, and ends with a conclusion and “where we’re
going next,” building up a natural, logical, and consequential narrative.
➤ Alessio Salvadorini
Creative Technologist, Nokia
Great book for anyone who wants to start grasping Flutter.
➤ Erdem Orman
Software Development Engineer, Amazon
If you want or need to do cross-platform mobile app development, you should
have this book at hand. Programming Flutter, by Carmine Zaccagnino, walks you
systematically through this important Google platform for building full apps that
work with Android, iOS, and Google Fuchsia.
➤ John Barry
Independent Editorial Consultant, various
Carmine’s hands-on tutorial will help you understand Flutter and why it is the
best solution to target iPhones and Androids with a single codebase. Great book
for a great framework!
➤ Paul Freiberger
Coauthor, Fire in the Valley: The Birth and Death of the Personal Computer
Programming Flutter
Native, Cross-Platform Apps the Easy Way
Carmine Zaccagnino
The Pragmatic Bookshelf
Raleigh, North Carolina
Many of the designations used by manufacturers and sellers to distinguish their products
are claimed as trademarks. Where those designations appear in this book, and The Pragmatic
Programmers, LLC was aware of a trademark claim, the designations have been printed in
initial capital letters or in all capitals. The Pragmatic Starter Kit, The Pragmatic Programmer,
Pragmatic Programming, Pragmatic Bookshelf, PragProg and the linking g device are trade-
marks of The Pragmatic Programmers, LLC.
Every precaution was taken in the preparation of this book. However, the publisher assumes
no responsibility for errors or omissions, or for damages that may result from the use of
information (including program listings) contained herein.
Our Pragmatic books, screencasts, and audio books can help you and your team create
better software and have more fun. Visit us at https://pragprog.com.
The team that produced this book includes:
Publisher: Andy Hunt
VP of Operations: Janet Furlow
Executive Editor: Dave Rankin
Development Editor: Michael Swaine
Copy Editor: Jasmine Kwityn
Indexing: Potomac Indexing, LLC
Layout: Gilson Graphics
For sales, volume licensing, and support, please contact [email protected].
For international rights, please contact [email protected].
Copyright © 2020 The Pragmatic Programmers, LLC.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system,
or transmitted, in any form, or by any means, electronic, mechanical, photocopying, recording,
or otherwise, without the prior consent of the publisher.
ISBN-13: 978-1-68050-695-2
Encoded using the finest acid-free high-entropy binary digits.
Book version: P1.0—February 2020
Contents
Acknowledgments . . . . . . . . . . . ix
Preface . . . . . . . . . . . . . . xi
Part I — Getting Started with Flutter
1. Making Your First Flutter App . . . . . . . . . 3
Get Familiar with Dart Syntax and Flutter Classes 3
Give the App Your Personal Touch 13
Where We’re Going Next 25
2. Laying Out More Widgets . . . . . . . . . 27
Introducing Layout Widgets 28
Contain and Add Padding to Widgets Using
Invisible Layout Widgets 28
Add Your Own Assets to the App 33
Displaying Images 35
Vertical Layout 41
Horizontal Layout: The Row 59
Making Grids 63
The Card 67
Fill the Space Available in the View Using Expanded 71
Slivers, Custom Scrollables, and Collapsable App Bars 73
The Key 74
Where We’re Going Next 75
3. Building a Calculator App . . . . . . . . . 77
Importing Basic Dependencies 77
Writing main 77
The Calculator’s Home Page 79
How the App Will Be Structured 79
Contents • vi
Implement the Basic Layout 80
Let’s Give the Calculator a Screen 82
Add the Deletion Row 83
The Third Row 84
Why a GridView Wouldn’t Work 88
Make the App Look and Work Right with Expanded 88
The Finished Layout 92
Implement the Calculations 98
Use the Calculation Inside the App 107
Wrapping Up the Calculator 108
What If We Try to Divide by 0? 115
Where We’re Going Next 118
4. Beyond the Standard Library: Plugins and Packages . . 119
An Introduction to Packages 119
Package Usage Example 122
Making Your Own Packages 129
Publishing a Package to Pub 137
Packages for Windows, macOS, and Linux 137
Where We’re Going Next 138
Part II — Doing More with Flutter
5. Network and Storage I/O and Navigation . . . . . 141
The API 141
The http Package 143
Writing Methods to Fetch Comics 147
What You Need to Build the UI: Navigation and the
InheritedWidget 149
Build the App’s Basic UI 167
Building the Comic Page 173
Using the CircularProgressIndicator 176
Making Everything Faster by Caching to Local Storage 177
Allowing the User to Click the Image and Go to the Website:
The url_launcher Package 184
Adding Comic Selection by Number 187
Permanent Data I/O in Flutter: Adding “Starred” Comics 191
Where We’re Going Next 200
Contents • vii
6. Testing and Debugging Flutter Apps . . . . . . 201
Testing 201
Testing the XKCD App: Using Mock Objects 211
Throwing and Catching Exceptions 233
Assert Statements 236
Where We’re Going Next 236
7. Build a Chat App Using Firebase . . . . . . . 237
What Is Firebase? 237
Animations and Transistions 246
Custom Shapes and Drawing in Flutter Apps Using Painters 250
The StreamBuilder 260
Building the Chat App 260
Where You’re Going Next 283
A1. Introduction to Dart . . . . . . . . . . 285
Comments in Dart 285
Variables and Conditions 286
Functions 295
main 297
Asynchronous Code in Dart: The dart:async Library 297
Conditional Constructs and Expressions 303
Loops: while, do while, and for 305
Classes 306
Typedef and Callbacks 311
Mastering import 312
Conversion Between Native Java/Apple and Dart Data Types 313
Where You’re Going Next 314
A2. Apple-Like Look and Additional App Configuration . . . 315
Cupertino Widgets 315
pubspec.yaml 326
Platform-Specific Setup 327
Index . . . . . . . . . . . . . . 331
Acknowledgments
This book exists because Flutter was released and such a revolutionary
technology needed a way for people to know about it and learn it however
they prefer. So, before even talking about the book, it’s necessary to remember
how good it is for the developer community that Google has released Flutter
and they’re continuing to invest in it to make it even more revolutionary and
important every day that passes.
Talking about the book, it has to be said that working with the Pragmatic
Bookshelf has been great. First of all, I want to thank Andy Hunt, who as a
publisher has built a wonderful team: starting from my very first interactions
with Brian MacDonald over my proposal to write this book everyone has been
thorough, welcoming, and helpful.
In particular, I want to thank Michael Swaine who, as the editor of this book,
has been encouraging, helpful, and understanding throughout the process,
never making me feel pressured and always helping and encouraging me
when any issues arose or when I had questions about anything related to
the book.
When bigger and more technical issues arose, production manager Janet
Furlow has fixed them, allowing me to keep working on the content of the
book instead. The cover Gilson Graphics made for the book is very nice as a
visual metaphor of Flutter’s multi-platform nature. In addition to those I have
mentioned, I want to thank everyone else at the Pragmatic Bookshelf who
has been involved in making the book as good as it is.
I want to thank everybody who has looked at the book and given me feedback,
which I have taken on and tried to use to the best of my ability to make the
book better for everyone. In particular, the technical reviewers who have been
thorough and thoughtful in their feedback and the beta book readers who
have taken their time to submit errata: it’s been very important and seeing
how thorough they have been has encouraged me to do as much as I could
report erratum • discuss