Book Image

Hands-On Mobile and Embedded Development with Qt 5

By : Lorn Potter
Book Image

Hands-On Mobile and Embedded Development with Qt 5

By: Lorn Potter

Overview of this book

Qt is a world-class framework, helping you to develop rich graphical user interfaces (GUIs) and multi-platform applications that run on all major desktop platforms and most mobile or embedded platforms. The framework helps you connect the dots across platforms and between online and physical experience. This book will help you leverage the fully-featured Qt framework and its modular cross-platform library classes and intuitive APIs to develop applications for mobile, IoT, and industrial embedded systems. Considerations such as screen size, device orientation changes, and small memory will be discussed. We will focus on various core aspects of embedded and mobile systems, such as connectivity, networking, and sensors; there is no IoT without sensors. You will learn how to quickly design a flexible, fast, and responsive UI that looks great. Going further, you will implement different elements in a matter of minutes and synchronize the UI elements with the 3D assets with high precision. You will learn how to create high-performance embedded systems with 3D/2D user interfaces, and deploy and test on your target hardware. The book will explore several new features, including Qt for WebAssembly. At the end of this book, you will learn about creating a full software stack for embedded Linux systems using Yocto and Boot to Qt for Device Creation.
Table of Contents (23 chapters)
Title Page
Dedication
About Packt
Foreword
Contributors
Preface
Index

Creating and opening a database


For the SQLite database, once we open it, it creates the database on the filesystem. For MySQL, we have to send MySQL commands to create the database. We construct the SQL query using QSqlQuery do this in MySQL. QSqlQuery takes the database object as an argument:

QSqlQueryquery(db);

To send a query, we call the exec() function on the QSqlQuery object. It takes a String as a typical query syntax:

QStringdbname="MAEPQTdb";
if (!query.exec("CREATEDATABASEIFNOTEXISTS"+dbname)) {
    qWarning() << "Database query error" << query.lastError().text();
}

 

dbname here is any String we want the database name to be; I am using MAEPQT db.

If this command fails, we issue a warning message. If it succeeds, then we go on and issue the command to USE it, so we call another query command:

query.exec("USE"+dbname);

From here, we need to create some tables. I will keep it simple and fill it with some data.

We start another query, but with an empty command, and the db object...