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Qt5 C++ GUI Programming Cookbook
Qt5 C++ GUI Programming Cookbook

Qt5 C++ GUI Programming Cookbook: Practical recipes for building cross-platform GUI applications, widgets, and animations with Qt 5 , Second Edition

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Qt5 C++ GUI Programming Cookbook

Event Handling - Signals and Slots

In this chapter, we will cover the following recipes:

  • New signals and slots syntax
  • UI events with signals and slots
  • Asynchronous programming made easier
  • Function callbacks

Introduction

The signals and slots mechanism in Qt 5 is one of its most important features. It's a method that allows communication between objects, which is a crucial part of a program's graphical user interface. A signal can be emitted from any QObject objects or its subclasses, which will then trigger any slot functions of any objects that are connected to the signal.

Compared to callbacks (which Qt 5 also support), the signals and slots mechanism is comparably more fluid and flexible for the programmer to use. The signals and slots mechanism is both type safe and not strongly coupled to the processing function, which makes it better than the callback's implementation.

A signal of an arbitrary class can trigger any private slots of an unrelated class that is going to be invoked, which is not possible with callbacks.
...

Technical requirements

New signals and slots syntax

The signals and slots mechanism has gone through some changes in the recent version of Qt, most notably its coding syntax. Qt 5 continues to support the older syntax for future releases, but there is no mention of how long it will be before it will be dropped completely. Therefore, it's better for us to start learning the new syntax before that day comes.

How to do it...

Let's get started by following these steps:

  1. Let's create a Qt Widgets Application project and open up mainwindow.ui.
  2. Drag and drop a PushButton from the Widget Box to the UI canvas:
  1. Right-click on the PushButton and select Go to slot. A window will appear:
  1. You will see a list of built-in slot functions available...

UI events with signals and slots

In the previous example, we demonstrated the use of signals and slots on a push button. Now, let's explore the signals and slots that are available in other common widget types.

How to do it...

To learn how to use signals and slots with UI events, follow these steps:

  1. Let's create a new Qt Widgets Application project.
  2. Drag and drop a Push Button, Combo Box, Line Edit, Spin Box, and Slider from the Widget Box into your UI canvas:
  1. Then, right-click on the push button and select clicked() and press the OK button to proceed. A slot function will be created for you by Qt Creator:
  1. Repeat the previous step, but this time, select the next selection until every function in QAbstractButton...

Asynchronous programming made easier

Since the signals and slots mechanism is asynchronous in nature, we can make use of it for things other than user interfaces. In programming terms, an asynchronous operation is a process that works independently, allowing the program to continue its operation without waiting for the process to complete, which may stall the whole program.

Qt 5 allows you to make use of its signals and slots mechanism to easily achieve asynchronous processes without much effort. This is even more true after Qt 5 introduced the new syntax for signals and slots, which allows a signal to trigger a normal function instead of a slot function from a QObject.

In the following example, we will further explore this opportunity and learn how we can improve our program's efficiency by using asynchronous operations through the signals and slots mechanism that's...

Function callbacks

Even though Qt 5 supports the signals and slots mechanism, some of the features in Qt 5 still use function callbacks, such as keyboard input, window resize, graphics painting, and others. Since these events only need to be implemented once, there is no need to use the signals and slots mechanism.

How to do it...

Let's get started by following this example:

  1. Create a Qt Widgets Application project, open up mainwindow.h, and add the following headers:

#include <QDebug>
#include <QResizeEvent>
#include <QKeyEvent>
#include <QMouseEvent>

  1. Then, declare these functions in mainwindow.h:
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();

void resizeEvent(QResizeEvent...
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Key benefits

  • Learn to use Qt 5 to design and customize the look and feel of your application
  • Improve the visual quality of an application by using graphics rendering and animation
  • Understand the balance of presentation and web content that will make an application appealing yet functional

Description

With the growing need to develop GUIs for multiple targets and multiple screens, improving the visual quality of your application becomes important so that it stands out from your competitors. With its cross-platform ability and the latest UI paradigms, Qt makes it possible to build intuitive, interactive, and user-friendly user interfaces for your applications. Qt5 C++ GUI Programming Cookbook, Second Edition teaches you how to develop functional and appealing user interfaces using the latest version of QT5 and C++. This book will help you learn a variety of topics such as GUI customization and animation, graphics rendering, implementing Google Maps, and more. You will also be taken through advanced concepts like asynchronous programming, event handling using signals and slots, network programming, various aspects of optimizing your application. By the end of the book, you will be confident to design and customize GUI applications that meet your clients' expectations and have an understanding of best practice solutions for common problems.

Who is this book for?

This intermediate-level book is designed for those who want to develop software using Qt 5. If you want to improve the visual quality and content presentation of your software application, this book is for you. Prior experience of C++ programming is required.

What you will learn

  • Animate GUI elements using Qt5 s built-in animation system
  • Draw shapes and 2D images using Qt5 s powerful rendering system
  • Implement an industry-standard OpenGL library in your project
  • Build a mobile app that supports touch events and exports it onto devices
  • Parse and extract data from an XML file and present it on your GUI
  • Interact with web content by calling JavaScript functions from C++
  • Access MySQL and SQLite databases to retrieve data and display it on your GUI
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Publication date : Mar 27, 2019
Length: 428 pages
Edition : 2nd
Language : English
ISBN-13 : 9781789803822
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Table of Contents

14 Chapters
Look-and-Feel Customization with Qt Designer Chevron down icon Chevron up icon
Event Handling - Signals and Slots Chevron down icon Chevron up icon
States and Animations with Qt and QML Chevron down icon Chevron up icon
QPainter and 2D Graphics Chevron down icon Chevron up icon
OpenGL Implementation Chevron down icon Chevron up icon
Using Network and Managing Large Documents Chevron down icon Chevron up icon
Threading Basics - Asynchronous Programming Chevron down icon Chevron up icon
Building a Touch Screen Application with Qt5 Chevron down icon Chevron up icon
XML Parsing Made Easy Chevron down icon Chevron up icon
Conversion Library Chevron down icon Chevron up icon
Accessing Databases with SQL Driver and Qt Chevron down icon Chevron up icon
Develop Web Applications using Qt WebEngine Chevron down icon Chevron up icon
Performance Optimization Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
(4 Ratings)
5 star 25%
4 star 0%
3 star 25%
2 star 50%
1 star 0%
Terrence Andrews May 22, 2019
Full star icon Full star icon Full star icon Full star icon Full star icon 5
As someone new to Qt5 and C++ in this cookbook provides you with great examples and philosophy to get the job done
Amazon Verified review Amazon
Amazon Customer May 06, 2019
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
Used for my projects
Amazon Verified review Amazon
hehedaozuiteng Dec 29, 2019
Full star icon Full star icon Empty star icon Empty star icon Empty star icon 2
good book for qt beginer, but have some errors though the whole book. Cannot find the way to connect the author.
Amazon Verified review Amazon
Mike Torchia Feb 05, 2024
Full star icon Full star icon Empty star icon Empty star icon Empty star icon 2
Typos, missing code, screenshots that dont match. Steer clear
Amazon Verified review Amazon
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