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

Executing queries


So far, we have been running queries, but not getting any data in return. One of the points of a database is to query for data, not just to enter it. What fun would it be if we could only input data? The Qt API has a way to accommodate the different syntax and millions of ways a query can be made. Most of the time, it is specific to the type of data you need to be returned, but also specific to the database data itself. Luckily, QSqlQuery is general enough that the query parameter is a string.

QSqlQuery

To retrieve data, execute a query using QsqlQuery and then operate on the records using the following functions:

  • first()
  • last()
  • next()
  • previous()
  • seek(int)

The first() and last() functions will retrieve the first and last records respectively. To iterate backward through the records, use previous(). The seek (int) function takes on integer as an argument to determine which record to retrieve.

We will usenext(), which will iterate forward through the records found in the query:

QSqlDatabasedb...