Qt in C++ Tutorial
Qt is a sophisticated C++ framework that focuses on building graphical user interfaces (GUIs) and provides a variety of libraries and tools for building cross-platform applications. For creating cross-platform applications focusing on graphical user interfaces (GUIs), Qt is a reliable and well-liked C++ framework.
It offers a vast selection of programmable widgets, APIs, and modules that enable programmers to create reliable, efficient, and attractive applications that function flawlessly on several operating systems, including macOS, Windows, Linux, iOS, and Android.
Prerequisites:
- Basic knowledge of C++ programming language.
- Familiarity with Qt fundamentals is helpful but optional.
How to Download Qt
Below are the following steps to download qt:
1. Visit the Qt website: Go to the official Qt website in your web browser at https://www.qt.io/download.
2. Decide on the Version: There are numerous alternatives for Qt versions on the download page. Choose the version that best meets your requirements. The most recent stable version is wise if you need help deciding which to select.
3. Choosing an Operating System: Select your operating system from the choices offered. Windows, macOS, and other Linux distributions are all supported by Qt.
4. Select the Installation Technique: Qt Online Installer and Qt Offline Installer are the most frequently available installation options.
You can select the components per your requirement using the Qt Online Installer, a compact executable file. During installation, the required files will be downloaded.
The offline installer for Qt is a larger file that includes all the required parts. Installing Qt on a computer without an internet connection can be helpful.
Select the installer based on your needs. The online installer is typically suggested since you may customize the installation and download only the required components.
5. Run the Installer: After downloading the installer, you can begin the installation process by running it.
6. The Licence Agreement is accepted: To continue the installation, read and agree on the Qt End-User Licence Agreement (EULA).
7. Select Installation place: A place for the installation will be presented to you. Wherever you wish to install Qt, you may use the default directory or give a specific path.
8. Select Components: When using the online installer, you will be shown a list of available components for installation. Select the tools you require to construct C++ applications, such as the Qt widgets module.
9. Download and install: If utilizing the online installer, the installer will download the required files after you choose the components and then carry out the installation.
10. Finished with the installation: You need to get a confirmation message once the installation is done. Your system has Qt installed at this point.
11. Establish Your Development Environment: An IDE like Qt Creator should be able to determine the installed Qt version for you. Qt projects can be started right away.
You should configure the addition of library paths to point to your Qt installation for use with other IDEs or command-line development. For information on how to set up your development environment, consult the manuals for your IDE or Qt.
Now that your computer has installed Qt, you can create C++ apps using its robust libraries and features. Remember to monitor the Qt Maintenance Tool installed with Qt for updates to keep your installation current.
Creating a Basic Qt Application
1. Open Qt Creator in step one: On your computer, launch Qt Creator.
2. Create a New Project: Select "New Project" or choose File > New File or Project from the menu. From selecting project templates, choose "Qt Widgets Application" and click "Choose."
3. Configure the project: Choose a name for your project and a place for its creation. Press "Next."
- Select the appropriate kit for the platform you wish to use to develop the application. In case you need clarification, use the default kit.
- Press "Next." Select the main window's class. Choose "Main Window" as the form's primary form class. Choose "Finish."
4. The user interface design: The "Design" tab is on the screen's left side in Qt Creator. It can be clicked to launch the GUI designer.
- Widgets can be added to the form in the center by dragging them from the "Widget Box" on the left. For instance, add a "Label" and a "Button" widget.
- You can change the widgets' properties in the "Properties" box on the right.
- Put the widgets in any order you desire on the form.
5. Connecting Slots and Signals: Right-click the "Button" widget in the form's "Edit" mode and choose "Go to slot..."
- The "Edit Go to Slot" dialogue will then be shown. Click "OK" after selecting the "clicked()" signal.
- Doing so will add a new slot to the "MainWindow" class in the "mainwindow. h" file for the button click event.
- In the "mainwindow.cpp" file, implement the slot function.
Example:
#include "mainwindow.h" #include "ui_mainwindow.h" #include <QMessageBox> MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) , ui(new Ui::MainWindow) { ui->setupUi(this); } MainWindow::~MainWindow() { delete ui; } void MainWindow::on_pushButton_clicked() { QMessageBox::information(this, "Button Clicked", "Hello, World!"); }
6. Build and launch the application: Either click the green "Play" button in Qt Creator or select "Build" > "Build Project" from the menu to build the application.
- After a successful build, click the green "Run" triangle or select "Build" > "Run" from the menu to start the program.
- The user interface you built will be shown when the application launches.
- When you press the button that you have created, a message box with the words "Hello, World!" will appear. Congratulations! You used C++ to build a simple Qt application. Although Qt is a robust framework with many capabilities and tools for developing complicated applications with stunning user interfaces, this lesson covers the fundamentals. You can examine the Qt documentation and other tutorials to learn more about Qt development.
Explanation:
A window with a label and a button will appear when you launch the Qt program.
Depending on how you configure the label in the form, the label may have some default text or none.
When you press the button that is created, a message box with the words "Hello, World!" will show up.
To see the actual output on your PC, please follow this tutorial's instructions and launch the Qt application in Qt Creator. The Qt application's graphical user interface (GUI) will show the output.
Widgets and Layouts
Fundamental Qt components, known as widgets and layouts, enable programmers to design interactive graphical user interfaces (GUIs) for their applications. Layouts neatly arrange UI elements like buttons, labels, text boxes, checkboxes, and more within the application's window. Widgets are these UI elements. Let's examine Qt's widgets and layouts:
1. Widgets in QT:
In Qt, widgets serve as the foundation for all GUI applications. They stand in for numerous graphical elements that consumers can engage with. Qt offers a wide variety of pre-built widgets with sophisticated features. Among the often-used widgets are:
- Qlabel: Displays text or images using QLabel.
- QPushButton: A push-button that can be clicked and sends out a "clicked" signal.
- QCheckBox: A checkbox that may be checked or unchecked is a QCheckBox.
- QRadioButton: A radio button part of a set of mutually exclusive alternatives.
- QLineEdit: A text input field with a single line.
- QTextEdit: A multiline text editor is QTextEdit.
- QSlider: A slider that enables users to choose a value from a range is called a QSlider.
- QComboBox: An option list in a drop-down menu.
These are only a few of Qt's many widgets; there are many more. Each widget includes a set of customizable characteristics, signals, and slots.
Example for QPushButton:
The QPushButton class in Qt C++ can be used to construct buttons. A widget called QPushButton simulates a standard push button. When the button is clicked, it generates a "clicked()" signal, which you may attach to a slot to carry out operations in reaction to the button click.
How to add a simple button to a Qt application:
- In Qt Creator, start a new Qt Widgets Application project.
- Use the Qt Designer to display the mainwindow.ui form.
- Drag and drop a "Push Button" widget from the Widget Box onto the form.
Example 1:
As an alternative, you can programmatically build a QPushButton in the mainwindow.cpp file:
// Include the necessary header files #include <QPushButton> #include <QVBoxLayout> #include <QMainWindow> // Inside the constructor of the main window class (MainWindow), add the following code to create the button: MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) { // Create the push button QPushButton *button = new QPushButton("Click Me", this); // Connect the clicked() signal of the button to a slot function connect(button, &QPushButton::clicked, this, &MainWindow::onButtonClicked); // Create a layout to arrange the button on the main window QVBoxLayout *layout = new QVBoxLayout; layout->addWidget(button); // Create a central widget and set the layout on it QWidget *centralWidget = new QWidget; centralWidget->setLayout(layout); // Set the central widget of the main window setCentralWidget(centralWidget); } // Implement the slot function that will be called when the button is clicked void MainWindow::onButtonClicked() { // Perform some action here // For example, display a message box QMessageBox::information(this, "Button Clicked", "Hello, World!"); }
Output:
The above code generates a main window with a "Click Me" button. When you press the click me button, a message box with the words "Hello, World!" will appear.
Example 2:
Creating a window with a label and a button. The label text will change when the button is clicked:
// main.cpp #include <QApplication> #include <QPushButton> #include <QLabel> int main(int argc, char *argv[]) { QApplication app(argc, argv); // Create a QLabel with the initial text "Hello, Qt!" QLabel label("Hello, Qt!"); // Create a QPushButton with the text "Change Text." QPushButton button("Change Text"); // Connect the clicked signal of the button to a lambda function QObject::connect(&button, &QPushButton::clicked, [&]() { label.setText("Text Changed!"); }); // Create a QVBoxLayout to arrange the label and button vertically QVBoxLayout layout; layout.addWidget(&label); layout.addWidget(&button); // Create a QWidget as the main window and set the layout QWidget window; window.setLayout(&layout); // Show the main window and start the event loop window.show(); return app.exec(); }
Output:
Repeat the previous procedures to run this program:
- Open a new "Qt Console Application" project in Qt Creator.
- Replace the code provided above with the content of the project's main.cpp file.
- Create and manage the project. The label and button should show up in a window.
- When you press the button, the label's text will change.
2.Layouts in Qt:
In a container, such as a window or a dialogue, layouts control the positioning and scaling of widgets. To make the GUI adaptable to various screen sizes, Qt has many layout classes that automatically change the size and position of widgets as the window is resized. In Qt, the main layout classes are:
- QVBoxLayout: Widgets are stacked vertically in a column using QVBoxLayout.
- QHBoxLayout: Positions widgets in a row horizontally.
- QGridLayout: Widgets are arranged in a grid-like layout with rows and columns using QGridLayout.
- QFormLayout: Creates a form-like layout with labels and input fields using QFormLayout.
Characteristics of Qt in C++
- Cross-Platform Compatibility: One of Qt's key benefits is its ability to write code only once and use it across various systems without requiring significant changes. The platform abstraction layer in Qt makes this possible by letting developers concentrate on functionality rather than platform-specific concerns.
- GUI Development: Qt's primary strength is its ability to create user interfaces. It offers a large selection of programmable widgets and building blocks for creating user interfaces that are simple to use and visually appealing. To maintain a unified appearance across several platforms, Qt also enables styling and theming.
- Signal-Slot Mechanism: Qt handles communication between objects using a robust signal-slot mechanism. Event handling may be readily implemented thanks to this method, which simplifies and reduces the likelihood of mistakes in GUI programming.
- Object-Oriented Design: Qt uses an object-oriented design philosophy and offers classes and frameworks to help programmers create modular, maintainable code.
- Internationalization and Localization: Qt supports these processes, enabling applications to be translated into several languages and quickly adapt to regional conditions.
- Connectivity and networking: Qt provides comprehensive networking support, making it simple to construct client-server applications and communicate via protocols like HTTP, TCP, UDP, etc.
- Multithreading: Qt offers multithreading capability, enabling programmers to design responsive applications that use numerous threads for activities like background processing or concurrent operations.
- File System Access: Qt's classes for managing files and directories make it simple to handle file operations, including reading, writing, and manipulation.
- 3D graphics: Visualisations, simulations, and interactive 3D applications can all be made with Qt 3D.
- Open-Source and Commercial Licencing: Qt offers open-source and corporate licensing options. The commercial version, Qt for Application Development, offers more functionality and support for bigger businesses. In contrast, the open-source version, Qt Open Source, is appropriate for most projects.
We learned how to build a straightforward Qt application with a button that launches a message box in this short Qt C++ tutorial. This tutorial covered constructing the main window with a button, configuring the development environment, and using signals and slots to manage user interactions. This tutorial can be a starting point for readers to investigate more complex Qt features and create more complex applications.