**Course Title:** QML Application Development **Section Title:** Integrating with C++ **Topic:** Integrating a C++ backend into your QML application.(Lab topic) **Objective:** In this lab, you'll learn how to integrate a C++ backend into your QML application, enabling you to leverage the power of C++ in your QML projects. By the end of this lab, you'll have hands-on experience creating a simple C++-QML integrated application. **Prerequisites:** Before proceeding with this lab, ensure that you have: 1. Completed the previous topics in the course, particularly "Integrating with C++". 2. A basic understanding of C++ programming concepts. 3. Qt Creator or another IDE of your choice installed and set up. **Lab Overview:** In this lab, we'll create a simple C++-QML integrated application that displays a list of employees and allows users to add new employees. We'll cover the following topics: 1. Creating a C++ backend class to manage employee data. 2. Exposing the C++ class to QML using the QML_CXX_MAP macro. 3. Creating a QML interface to interact with the C++ backend. 4. Connecting the QML interface to the C++ backend using signal-slot connections. **Step 1: Create a C++ Backend Class** Create a new C++ class called `EmployeeManager` to manage employee data. This class will have the following methods: * `addEmployee`: Adds a new employee to the list. * `getEmployees`: Returns a list of all employees. ```cpp // employee_manager.h #ifndef EMPLOYEE_MANAGER_H #define EMPLOYEE_MANAGER_H #include <QObject> #include <QString> #include <QList> class EmployeeManager : public QObject { Q_OBJECT Q_PROPERTY(QList<QString> employees READ getEmployees WRITE setEmployees NOTIFY employeesChanged) public: EmployeeManager(QObject *parent = nullptr); QList<QString> getEmployees() const; void addEmployee(const QString &employeeName); signals: void employeesChanged(); private: QList<QString> employees_; }; #endif // EMPLOYEE_MANAGER_H ``` ```cpp // employee_manager.cpp #include "employee_manager.h" EmployeeManager::EmployeeManager(QObject *parent) : QObject(parent) {} QList<QString> EmployeeManager::getEmployees() const { return employees_; } void EmployeeManager::addEmployee(const QString &employeeName) { employees_.append(employeeName); emit employeesChanged(); } ``` **Step 2: Expose the C++ Class to QML** To expose the `EmployeeManager` class to QML, use the `QML_CXX_MAP` macro in the `main.cpp` file: ```cpp // main.cpp #include <QQmlApplicationEngine> #include <QQmlContext> #include "employee_manager.h" int main(int argc, char *argv[]) { // ... EmployeeManager employeeManager; engine.rootContext()->setContextProperty("employeeManager", &employeeManager); // ... } ``` **Step 3: Create a QML Interface** Create a QML interface to interact with the `EmployeeManager` class. This interface will have a `ListView` to display the employees and a `TextField` to add new employees. ```qml // EmployeeView.qml import QtQuick 2.15 import QtQuick.Controls 2.15 ListView { id: employeeListView model: employeeManager.employees delegate: Text { text: modelData } TextField { id: newEmployeeField placeholderText: "Enter new employee name" } Button { text: "Add Employee" onClicked: employeeManager.addEmployee(newEmployeeField.text) } } ``` **Step 4: Connect the QML Interface to the C++ Backend** Connect the QML interface to the C++ backend using signal-slot connections. When the `addEmployee` button is clicked, the `addEmployee` method of the `EmployeeManager` class will be called. ```qml // EmployeeView.qml Button { text: "Add Employee" onClicked: { employeeManager.addEmployee(newEmployeeField.text) newEmployeeField.text = "" } } ``` **Conclusion:** In this lab, you have successfully integrated a C++ backend into your QML application. You have created a simple C++-QML integrated application that displays a list of employees and allows users to add new employees. **Resources:** * Qt Documentation: [Exposing C++ Classes to QML](https://doc.qt.io/qt-6/qtqml-cppintegration-exposecppattributes.html) * Qt Documentation: [Connecting C++ and QML](https://doc.qt.io/qt-6/qtqml-cppintegration-interactqmlfromcpp.html) **Questions or Comments:** If you have any questions or comments about this lab, feel free to ask below. **Next Topic:** In the next topic, "Understanding QML's state and state machine," we will explore how to manage complex state changes in your QML applications. Please provide your feedback on this lab and suggest any improvements.