Table Of ContentHands-On Embedded
Programming with Qt
Develop high performance applications for embedded
systems with C++ and Qt 5
John Werner
BIRMINGHAM - MUMBAI
Hands-On Embedded Programming with Qt
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Contributors
About the author
John Werner is an internationally published author, engineer, consultant, and conference
speaker with more than 15 years' experience. He has earned patents for inventions ranging
from Inkjet printers to automotive ignition systems. John was one of the early users of Qt
on QNX and contributed to the early knowledge of how to make it work. He is a
contributor to the Qt-related information on Stack Exchange. He is currently a senior
software engineer, specializing in Qt development, for Caliber Imaging & Diagnostics.
I would like to acknowledge the following people and companies:
Qt, for providing trial licenses of their embedded products
My GoG family for their support and their endless humor
The team at Caliber Imaging & Diagnostics, my employer, for their
support and encouragement
Nick at La Salon Bianca, for making me look good
The editorial staff at Packt, for helping me walk through this process of writing
my first book
Most of all, my wife and children for their infinite understanding, patience,
and support
About the reviewer
Pablo Rogina was born and lives in Buenos Aires, Argentina. He earned his bachelor's
degree in computer science at Universidad de Buenos Aires (UBA) and holds a
postgraduate degree in information security, also from UBA. He has more than 25 years'
extensive experience and exposure to several different positions and responsibilities in IT
environments, ranging from programming to network administration, and including
system analysis and design, end user support, and database design and management. Over
the last few years, he has been focusing on embedded system development, with specific
exposure to IoT and computer vision solutions.
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Table of Contents
Preface 1
Section 1: Getting Started with Embedded Qt
Chapter 1: Setting Up the Environment 9
Technical requirements 9
Creating our embedded environment 10
Obtaining the hardware 11
Loading the firmware 11
Backing up the SD card 12
Identifying the SD card device 12
Grabbing the image 14
Burning a new image 14
Connections and first boot 14
Network configuration 15
Installing RSync 16
Preparing the host machine 17
Installing Qt 17
Setting up the cross compilation environment 19
Installing the cross compilation tools 19
Preparing for debugging 20
Accessing the Target's root directory on the host 20
Building Qt for the Target 21
Fixing the sources 22
Building a program 22
Configuring the Qt build 22
Decoding the configure command 23
Building the code 24
Synchronizing the new components with the target 25
Running a quick test to ensure how the program works 25
Summary 26
Questions 27
Further reading 27
Chapter 2: Writing Your First Qt Application 28
Technical requirements 29
Introducing Qt Creator 29
Starting Qt Creator 30
Qt Creator welcomes you 30
The Examples screen 31
The Tutorials screen 32
Table of Contents
The Projects screen 33
The left icon bar 34
Greetings from Qt 35
Creating a project 35
Walking through the New File or Project wizard 36
Choosing a template 37
Picking a name and location 38
Selecting a kit 38
Defining the main window class 39
Selecting a source control system for your project 40
Examining the Edit screen 42
Viewing projects and open files 42
A place for editing 43
Presenting outputs 43
Designing the UI 44
Placing a text label 45
Running the code 46
Protecting your work 47
Who are you? 48
Adding a place to type your name 48
Causing a response 49
Fixing a mistake 51
Launching our application in the Qt Creator debugger 52
Examining the Debug screen 52
Setting a breakpoint 53
Tripping the breakpoint 53
Getting some help 56
Digging deeper 57
Explaining the push button code 57
Sending and receiving between objects–signals and slots 59
Cool things about signals and slots 59
Rules of signals and slots 60
Testing 60
Summary 61
Questions 62
Further reading 62
Chapter 3: Running Your First Application on the Target 63
Technical requirements 63
Configuring Qt Creator for our Target 64
Telling Qt Creator about a new device 64
Telling Qt Creator about the cross-compiler 67
Configuring the debugger for the Target 69
Letting Qt Creator know about our Raspberry Pi Qt build 70
Creating a Qt kit 72
Building for the Target 72
Adding a kit to the project 73
[ ii ]
Table of Contents
Building the application 74
Deploying on the Target 74
Running the application on the Target 75
Making a more flexible display using layouts 76
Debugging on the Target 79
Troubleshooting debugging 79
Summary 80
Questions 81
Section 2: Working with Embedded Qt
Chapter 4: Important Qt Concepts 83
Technical requirements 83
Communicating effectively – signals and slots 84
Quick info – Signals and slots 84
Signals and slots in non-GUI code 85
Preparing the header 87
Using the QTimer 89
Setting up the timer 89
Connecting the QTimer signal 89
Finishing the code 90
Running our application 90
Signals and slots using lambdas 91
Queuing things up 93
When should I use a queued connection? 95
Implementing Signals Not Needed 96
Looking inside – Qt's introspection support 97
Properties 97
Q_PROPERTY 99
QVariant 100
Enums 102
Differing views — model/view architecture 103
A quick dive 104
Formalizing Qt's model/view 105
Customizing how model data is viewed 105
Filtering and sorting what's viewed 105
Keeping it portable – Qt's platform abstraction 106
Qt's OS and filesystem abstractions 107
Qt's container class abstractions 108
Taking a closer look at building and Main 108
Qt Creator's supported build systems 109
QMake 109
Qbs 109
CMake 109
What's all that in main(..)? 110
Summary 110
[ iii ]
Table of Contents
Questions 111
Chapter 5: Managing the Overall Workflow 112
Technical requirements 112
Modernizing software development 113
Falling down the development cycle 113
Continuous Integration 114
Unit testing 114
Modern development cycle 115
Moving ahead without hardware 115
Layering the problem 115
Starting our BigProject 116
BigProject customer requirements 116
Starting the Qt project 117
Initial main window design 117
Wiring up the time display 118
Testing 119
Commit it 120
Mocking the hardware 120
A new requirement 120
Defining the interface 121
Implementing the mock 122
Injecting the mock 123
Wiring up the temperature display 124
Test it! 124
Summary 125
Questions 126
Further reading 126
Chapter 6: Exploring GUI Technologies 128
Technical requirements 128
Two roads diverge 129
Qt Widgets 129
Programming widgets 130
Creating a widget with Qt Creator/Designer 130
Creating a widget by hand 135
Doing something new – QML 136
What is QML? 137
Developing a UI in QML 138
Revisiting some old friends 138
Hello from Qt! 138
Hello from QML! 139
Creating the project 139
Defining the window 140
Customizing the display 143
Using the Designer 144
The Form Editor 145
[ iv ]
