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Basics of the Qt framework and its tools for developing embedded GUIs
Jincheol Park edited this page Jul 23, 2024
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Qt is a powerful cross-platform application development framework widely used for developing graphical user interfaces (GUIs) in embedded systems. It is utilized in various industries such as automotive, consumer electronics, and mobile devices. Qt provides a comprehensive set of C++ libraries and tools to facilitate the development process.
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History and Overview of Qt
- Qt was first developed in 1991 and is currently maintained by The Qt Company.
- It supports cross-platform development, enabling applications to run on Windows, macOS, Linux, Android, iOS, and more.
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Main Components of Qt
- Qt Core: Provides essential data structures and functions (e.g., strings, files, date/time handling).
- Qt GUI: Offers components for creating graphical user interfaces (e.g., windows, buttons, text fields).
- Qt Widgets: A set of widgets for building traditional desktop-style GUIs.
- Qt Quick: Uses QML to build modern, dynamic user interfaces easily.
- Qt Network: Provides classes for network communication.
- Qt Multimedia: Features for developing multimedia applications (e.g., audio, video playback).
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Qt Creator
- An integrated development environment (IDE) for developing Qt applications.
- Includes a code editor, debugger, graphical layout designer, and other tools.
- Project templates make it easy to start new projects quickly.
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Qt Designer
- A tool for visually designing GUIs.
- Allows drag-and-drop placement of widgets and setting their properties.
- GUIs created with Qt Designer are saved as XML .ui files, which can be integrated with code.
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QML and Qt Quick
- QML (Qt Modeling Language) is a declarative language similar to JavaScript used for Qt Quick.
- Makes it easy to create complex animations and responsive UIs.
- Qt Quick, based on QML, allows the development of high-performance graphical user interfaces.
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Advantages of Qt for Embedded Systems
- Cross-platform support allows reuse across various embedded environments.
- Efficient memory management and performance optimization.
- Easy integration with various sensors and hardware components.
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Developing Embedded GUIs with Qt
- Setting Up Environment: Configure the toolchain and Qt libraries for the target embedded system.
- Designing UI: Use Qt Designer or QML to design the user interface.
- Writing Code: Implement application logic using C++ and QML.
- Testing and Debugging: Use Qt Creator's debugger to test and debug the application.
- Deployment: Deploy the application to the target embedded system.
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Creating a Simple GUI Application
- Create a new Qt Widgets Application project in Qt Creator.
- Add a button to the main window and write code to handle the button click event.
- Run the application to see it in action.
// main.cpp
#include <QApplication>
#include <QPushButton>
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
QPushButton button("Hello, Qt!");
button.resize(200, 60);
button.show();
return app.exec();
}-
Creating a Simple Application with QML
- Create a new Qt Quick Application project.
- Add a button in the QML file and handle the button click event.
// main.qml
import QtQuick 2.15
import QtQuick.Controls 2.15
ApplicationWindow {
visible: true
width: 640
height: 480
title: "Hello, QML!"
Button {
text: "Click me"
anchors.centerIn: parent
onClicked: {
console.log("Button clicked!")
}
}
}- Simplicity and Readability: QML's declarative syntax allows developers to describe the UI in a straightforward and readable manner. It resembles HTML and CSS, making it easier to define the structure and appearance of the UI.
- Separation of Concerns: By using QML for the UI and C++ for the application logic, you can maintain a clear separation of concerns, which improves code organization and maintainability.
- Faster Development: The declarative nature of QML, combined with the powerful Qt Quick elements, enables faster prototyping and development of UIs. You can quickly see the results of your changes without recompiling the entire application.
- Reusability: QML components can be easily reused across different parts of the application or even in different projects, promoting code reuse and reducing duplication.
- Rich Animations and Transitions: QML makes it simple to create rich, smooth animations and transitions with minimal code. The language includes built-in support for animation, making it easy to enhance the user experience.
- Responsive Design: QML's layout and positioning capabilities allow developers to create responsive designs that adapt to different screen sizes and orientations effortlessly.
- Data Binding: QML supports property bindings, allowing UI elements to automatically update when the underlying data changes. This reduces the need for manual synchronization between the UI and the application state.
- State Management: QML provides a straightforward way to manage different states and transitions between them. This is particularly useful for creating dynamic and interactive interfaces.
- Scripting: QML integrates seamlessly with JavaScript, allowing developers to use JavaScript for scripting within the QML files. This is useful for handling events, performing calculations, and managing application logic without diving into C++.
- Flexibility: The ability to use JavaScript within QML offers flexibility in implementing complex behaviors directly within the UI layer.
- Live Reload: Qt Creator supports live reloading of QML files, enabling developers to see the impact of their changes in real-time without restarting the application.
- Ease of Testing: The declarative nature of QML makes it easier to write unit tests for UI components. Testing frameworks like Squish for Qt provide tools specifically designed for QML-based applications.
- Cross-Platform Consistency: QML abstracts away platform-specific details, ensuring that the UI behaves consistently across different operating systems and devices.
- Unified Development: By using QML, developers can create applications that look and feel the same on various platforms, reducing the effort required to adapt the UI for each platform.
QML Example:
import QtQuick 2.15
import QtQuick.Controls 2.15
ApplicationWindow {
visible: true
width: 640
height: 480
title: "Button Animation with QML"
Button {
text: "Click me"
anchors.centerIn: parent
onClicked: {
console.log("Button clicked!")
}
SequentialAnimation {
loops: Animation.Infinite
NumberAnimation { target: button; property: "scale"; from: 1.0; to: 1.5; duration: 500 }
NumberAnimation { target: button; property: "scale"; from: 1.5; to: 1.0; duration: 500 }
}
}
}C++ Example:
#include <QApplication>
#include <QPushButton>
#include <QPropertyAnimation>
#include <QSequentialAnimationGroup>
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
QPushButton button("Click me");
button.resize(200, 60);
button.show();
QPropertyAnimation *animation1 = new QPropertyAnimation(&button, "geometry");
animation1->setDuration(500);
animation1->setStartValue(QRect(50, 50, 200, 60));
animation1->setEndValue(QRect(50, 50, 300, 90));
QPropertyAnimation *animation2 = new QPropertyAnimation(&button, "geometry");
animation2->setDuration(500);
animation2->setStartValue(QRect(50, 50, 300, 90));
animation2->setEndValue(QRect(50, 50, 200, 60));
QSequentialAnimationGroup *group = new QSequentialAnimationGroup;
group->addAnimation(animation1);
group->addAnimation(animation2);
group->setLoopCount(-1);
group->start();
QObject::connect(&button, &QPushButton::clicked, []() {
qDebug("Button clicked!");
});
return app.exec();
}